Heat and Segregation

Plant Signal Behav. 2020; 15(5): 1746985.
Heat stress interferes with chromosome segregation and cytokinesis during male meiosis in Arabidopsis thaliana
Xiaoning Lei, Yingjie Ning, Ibrahim Eid Elesawi, Ke Yang, Chunli Chen, Chong Wang, and Bing Liu

ABSTRACT
In higher plants, male meiosis is a key process of microsporogenesis and is crucial for plant fertility. Male meiosis programs are prone to be influenced by altered temperature conditions. Studies have reported that an increased temperature (28°C) within a fertile threshold can affect the frequency of meiotic recombination in Arabidopsis. However, not much has been known how male meiosis responses to an extremely high temperature beyond the fertile threshold. To understand the impact of extremely high temperature on male meiosis in Arabidopsis, we treated flowering Arabidopsis plants with 36-38°C and found that the high-temperature condition significantly reduced pollen shed and plant fertility, and led to formation of pollen grains with varied sizes. The heat stress-induced unbalanced tetrads, polyad and meiotic restitution, suggesting that male meiosis was interfered. Fluorescence in situ hybridization (FISH) assay confirmed that both homologous chromosome separation and sister chromatids cohesion were influenced. Aniline blue staining of tetrad-stage pollen mother cells (PMCs) revealed that meiotic cytokinesis was severely disrupted by the heat stress. Supportively, immunolocalization of ɑ-tubulin showed that the construction of spindle and phragmoplast at both meiosis I and II were interfered. Overall, our findings demonstrate that an extremely high-temperature stress over the fertile threshold affects both chromosome segregation and cytokinesis during male meiosis by disturbing microtubular cytoskeleton in Arabidopsis.

Scientific Reports  volume  7, Article number: 5281 (2017) 
High temperature-induced production of unreduced pollen and its cytological effects in Populus
Jun Wang, Daili Li, Fengnan Shang & Xiangyang Kang 

Abstract
Temperature change is of potential to trigger the formation of unreduced gametes. In this study, we showed that short periods of high temperature treatment can induce the production of 2n pollen in Populus pseudo-simonii Kitag. The meiotic stage, duration of treatment, and temperature have significant effects on the induction of 2n pollen. Heat stress resulted in meiotic abnormalities, including failure of chromosome separation, chromosome stickiness, laggards and micronuclei. Spindle disorientations in the second meiotic division, such as parallel, fused, and tripolar spindles, either increased in frequency or were induced de novo by high temperature treatment. We found that the high temperature treatment induced depolymerisation of meiotic microtubular cytoskeleton, resulting in the failure of chromosome segregation. New microtubular cytoskeletons were able to repolymerise in some heat-treated cells after transferring them to normal conditions. However, aberrant cytokinesis occurred owing to defects of new radial microtubule systems, leading to production of monads, dyads, triads, and polyads. This suggested that depolymerisation and incomplete restoration of microtubules may be important for high temperature-induction of unreduced gametes. These findings might help us understand how polyploidisation is induced by temperature-related stress and support the potential effects of global climate change on reproductive development of plants.

Front. Plant Sci., 26 September 2017
Sequencing of Single Pollen Nuclei Reveals Meiotic Recombination Events at Megabase
Resolution and Circumvents Segregation Distortion Caused by Postmeiotic Processes
Steven Dreissig, Jörg Fuchs, Axel Himmelbach, Martin Mascher, and Andreas Houben

Meiotic recombination is a fundamental mechanism to generate novel allelic combinations which can be harnessed by breeders to achieve crop improvement. The recombination landscape of many crop species, including the major crop barley, is characterized by a dearth of recombination in 65% of the genome. In addition, segregation distortion caused by selection on genetically linked loci is a frequent and undesirable phenomenon in double haploid populations which hampers genetic mapping and breeding. Here, we present an approach to directly investigate recombination at the DNA sequence level by combining flow-sorting of haploid pollen nuclei of barley with single-cell genome sequencing. We confirm the skewed distribution of recombination events toward distal chromosomal regions at megabase resolution and show that segregation distortion is almost absent if directly measured in pollen. Furthermore, we show a bimodal distribution of inter-crossover distances, which supports the existence of two classes of crossovers which are sensitive or less sensitive to physical interference. We conclude that single pollen nuclei sequencing is an approach capable of revealing recombination patterns in the absence of segregation distortion.

PLoS genetics, 14(5), [e1007384].
Elevated temperature increases meiotic crossover frequency via the interfering (Type I) pathway in Arabidopsis thaliana
Jennifer L Modliszewski, Hongkuan Wang, Ashley R Albright, Scott M Lewis, Alexander R Bennett, Jiyue Huang, Hong Ma, Yingxiang Wang, Gregory P Copenhaver

Abstract
For most eukaryotes, sexual reproduction is a fundamental process that requires meiosis. In turn, meiosis typically depends on a reciprocal exchange of DNA between each pair of homologous chromosomes, known as a crossover (CO), to ensure proper chromosome segregation. The frequency and distribution of COs are regulated by intrinsic and extrinsic environmental factors, but much more is known about the molecular mechanisms governing the former compared to the latter. Here we show that elevated temperature induces meiotic hyper-recombination in Arabidopsis thaliana and we use genetic analysis with mutants in different recombination pathways to demonstrate that the extra COs are derived from the major Type I interference sensitive pathway. We also show that heat-induced COs are not the result of an increase in DNA double-strand breaks and that the hyper-recombinant phenotype is likely specific to thermal stress rather than a more generalized stress response. Taken together, these findings provide initial mechanistic insight into how environmental cues modulate plant meiotic recombination and may also offer practical applications.

Philos Trans R Soc Lond B Biol Sci. 2017.
Are the effects of elevated temperature on meiotic recombination and thermotolerance linked via the axis and synaptonemal complex?
Christopher H. Morgan, Huakun Zhang and Kirsten Bomblies

Abstract
Meiosis is unusual among cell divisions in shuffling genetic material by crossovers among homologous chromosomes and partitioning the genome into haploid gametes. Crossovers are critical for chromosome segregation in most eukaryotes, but are also an important factor in evolution, as they generate novel genetic combinations. The molecular mechanisms that underpin meiotic recombination and chromosome segregation are well conserved across kingdoms, but are also sensitive to perturbation by environment, especially temperature. Even subtle shifts in temperature can alter the number and placement of crossovers, while at greater extremes, structural failures can occur in the linear axis and synaptonemal complex structures which are essential for recombination and chromosome segregation. Understanding the effects of temperature on these processes is important for its implications in evolution and breeding, especially in the context of global warming. In this review, we first summarize the process of meiotic recombination and its reliance on axis and synaptonemal complex structures, and then discuss effects of temperature on these processes and structures. We hypothesize that some consistent effects of temperature on recombination and meiotic thermotolerance may commonly be two sides of the same coin, driven by effects of temperature on the folding or interaction of key meiotic proteins.

Communications Biology  volume  3, Article number: 187 (2020) 
High temperatures alter cross-over distribution and induce male meiotic restitution in Arabidopsis thaliana
Nico De Storme & Danny Geelen

Abstract
Plant fertility is highly sensitive to elevated temperature. Here, we report that hot spells induce the formation of dyads and triads by disrupting the biogenesis or stability of the radial microtubule arrays (RMAs) at telophase II. Heat-induced meiotic restitution in Arabidopsis is predominantly SDR-type (Second Division Restitution) indicating specific interference with RMAs formed between separated sister chromatids. In addition, elevated temperatures caused distinct deviations in cross-over formation in male meiosis. Synapsis at pachytene was impaired and the obligate cross-over per chromosome was discarded, resulting in partial univalency in meiosis I (MI). At diakinesis, interconnections between non-homologous chromosomes tied separate bivalents together, suggesting heat induces ectopic events of non-homologous recombination. Summarized, heat interferes with male meiotic cross-over designation and cell wall formation, providing a mechanistic basis for plant karyotype change and genome evolution under high temperature conditions.

Front. Plant Sci., 25 May 2020
Analysis of Crossover Events and Allele Segregation Distortion in Interspecific Citrus Hybrids by Single Pollen Genotyping
Miguel Garavello, José Cuenca,Steven Dreissig, Jörg Fuchs, Luis Navarro, Andreas Houben, and Pablo Aleza

Abstract
In citrus, a classical method of studying crossovers and segregation distortion (SD) is the genetic analysis of progenies. A new strategy combining fluorescence-activated cell sorting and whole genome amplification of haploid pollen nuclei with a large set of molecular markers, offers the opportunity to efficiently determine the frequency of crossovers and the identification of SD without the need to generate segregating populations. Here we have analyzed meiotic crossover events in a pollen nuclei population from “Eureka” lemon and the allelic SD was evaluated in a pollen nuclei population from a clementine × sweet orange hybrid (“CSO”). Data obtained from the “CSO” pollen nuclei population were compared to those obtained from genotyping of a segregating population (“RTSO”) arising from a hand-made sexual hybridization between diploid non apomictic selected tangor (mandarin × sweet orange; “RTO” tangor) as female parent pollinated with “CSO” tangor as male parent. The analysis of crossovers rates on chromosome 1 revealed the presence of up to five crossovers events on one arm and four on the corresponding other arm, with an average of 1.97 crossovers per chromosome while no crossover events were observed in five “Eureka” lemon pollen nuclei. The rate of SD observed in “CSO” pollen nuclei (13.8%) was slightly lower than that recovered in the “RTSO” population (20.7%). In the pollen nuclei population, SD was found on linkage group (LG) 2, while the “RTSO” population showed SD on LGs 2 and 7. Potential male gametic selection mechanisms were distinguished in pollen grains, while in the population, mechanisms of gametophytic selection and/or zygotic selection were observed. This methodology is a very useful tool to facilitate research focused on the reproductive biology of citrus and study the mechanisms that affect crossovers and SD.

Journal of Experimental Botany, Volume 62, Issue 10, June 2011, Pages 3587–3597,
Polyploidization mechanisms: temperature environment can induce diploid gamete formation in Rosa sp. 
Yann Pécrix, Géraldine Rallo, Hélène Folzer, Mireille Cigna, Serge Gudin, Manuel Le Bris

Abstract
Polyploidy is an important evolutionary phenomenon but the mechanisms by which polyploidy arises still remain underexplored. There may be an environmental component to polyploidization. This study aimed to clarify how temperature may promote diploid gamete formation considered an essential element for sexual polyploidization. First of all, a detailed cytological analysis of microsporogenesis and microgametogenesis was performed to target precisely the key developmental stages which are the most sensitive to temperature. Then, heat-induced modifications in sporad and pollen characteristics were analysed through an exposition of high temperature gradient. Rosa plants are sensitive to high temperatures with a developmental sensitivity window limited to meiosis. Moreover, the range of efficient temperatures is actually narrow. 36 °C at early meiosis led to a decrease in pollen viability, pollen ectexine defects but especially the appearance of numerous diploid pollen grains. They resulted from dyads or triads mainly formed following heat-induced spindle misorientations in telophase II. A high temperature environment has the potential to increase gamete ploidy level. The high frequencies of diplogametes obtained at some extreme temperatures support the hypothesis that polyploidization events could have occurred in adverse conditions and suggest polyploidization facilitating in a global change context.

BMC Plant Biology  volume  19, Article number: 10 (2019) 
Meiotic abnormalities affect genetic constitution and pollen viability in dicots from Indian cold deserts
Dalvir Kaur & V. K. Singhal 

Background
Meiotic abnormalities lead to morphological and genetic variations which caused not only to evolution but also intraspecific reproductive barriers. During present study of detailed meiotic course in dicotyledonous plants sampled from Indian cold deserts, various meiotic abnormalities have been detected. For this, the plant materials fixed in Carnoy’s fixative and studied detailed meiotic course by standard squash method in 1% acetocarmine.

Results
Meiotic abnormalities have been presently detected in 71 species which include multiple associations in diploids (Achillea millefolium L.), multivalents and univalents in polyploids (4 species), cytomixis (40 species), chromosome stickiness (20 species), nonsynchronous disjunction of bivalents (32 species), interbivalent connections (15 species), synaptic mutants (2 species), syncyte meiocytes (2 species), abnormal spindles (7 species), and fusion of pollen grains (1 species), laggards and chromatin bridges, hypo-, hyperploid PMCs, monads, dyads, triads, tetrads with micronuclei and polyads.

Conclusions
Consequently, variable sized apparently fertile pollen grains and considerable amount of sterile pollen grains are resulted as end products which lead to different genetic constitution (aneuploids and polyploids) and curtailed sexual reproductive success in these species.

Theoretical and Applied Genetics volume  130, pages 1785–1800 (2017)
Short periods of high temperature during meiosis prevent normal meiotic
progression and reduce grain number in hexaploid wheat (Triticum aestivum L.)
Tracie Draeger & Graham Moore 

Abstract
This study assesses the effects of heat on meiotic progression and grain number in hexaploid wheat (Triticum aestivum L. var. Chinese Spring), defines a heat-sensitive stage and evaluates the role of chromosome 5D in heat tolerance. Plants were exposed to high temperatures (30 or 35 °C) in a controlled environment room for 20-h periods during meiosis and the premeiotic interphase just prior to meiosis. Examination of pollen mother cells (PMCs) from immature anthers immediately before and after heat treatment enabled precise identification of the developmental phases being exposed to heat. A temperature-sensitive period was defined, lasting from premeiotic interphase to late leptotene, during which heat can prevent PMCs from progressing through meiosis. PMCs exposed to 35 °C were less likely to progress than those exposed to 30 °C. Grain number per spike was reduced at 30 °C, and reduced even further at 35 °C. Chinese Spring nullisomic 5D-tetrasomic 5B (N5DT5B) plants, which lack chromosome 5D, were more susceptible to heat during premeiosis–leptotene than Chinese Spring plants with the normal (euploid) chromosome complement. The proportion of plants with PMCs progressing through meiosis after heat treatment was lower for N5DT5B plants than for euploids, but the difference was not significant. However, following exposure to 30 °C, in euploid plants grain number was reduced (though not significantly), whereas in N5DT5B plants the reduction was highly significant. After exposure to 35 °C, the reduction in grain number was highly significant for both genotypes. Implications of these findings for the breeding of thermotolerant wheat are discussed.

International Journal of Plant SciencesVolume 159, Number 4 pp. 616–626
Effects of temperature during microsporogenesis on pollen performance in Cucurbita pepo L. (Cucurbitaceae)
Magnús H. Jóhannsson, andAndrew G. Stephenson

Abstract
This study uses a wild and cultivated variety of Cucurbita pepo to examine the effects of temperature during pollen development on pollen performance and to examine the extent to which the effects of temperature on pollen performance are environmental or genetic. We found that pollen developed at 20°C (cool temperature) grew significantly longer pollen tubes in vitro than pollen developed at 30°C (warm temperature), and it sired significantly more seeds in competition with pollen developed at 30°C. Developmental temperature not only affected the speed of pollen tube growth in vivo, but it also affected the resulting sporophytic generation. Seeds sired by cool- and warm-developed pollen did not differ significantly in seed weight, but seeds sired by cool-developed pollen had significantly faster root growth after 24 h and 48 h, significantly greater seedling mass after 48 h, and larger leaf area at 7 d than seeds sired by warm-developed pollen. This indicates that at least some of the effects of temperature on pollen performance had a genetic basis. We also examined the segregation of four single gene morphological traits in backcrosses using pollen from F1 plants (cultivated ♀ x wild ♂ C. pepo) developed under warm and cool conditions. For one trait, the allele from the cultivar was found in a significantly higher percentage of the progeny sired by cool-developed pollen than in the warm-developed pollen, possibly indicating that the gene for this trait is linked to a temperature sensitive gene.

Naor: Temperature affects development, flowering dormancy in Calla (2002)

Cornejo: Calla, heat, bud dormancy (2003)

Ngamau: Selection for early flowering, temp. and salt tolerance, Calla (2006)

Genetics and Plant Breeding  Sci. agric. (Piracicaba, Braz.) 77 (3)  2020  
Influence of high temperature on the reproductive biology of dry edible bean (Phaseolus vulgaris L.)
Daiana Alves da Silva, Cecília Alzira Ferreira Pinto-Maglio, Érica Cristina de Oliveira, Raquel Luiza de Moura dos Reis, Sérgio Augusto Morais Carbonell, Alisson Fernando Chiorato

ABSTRACT
The aim of this study was to investigate the effect of heat stress on 12 bean genotypes through the analysis of their reproductive biology in terms of flowering, pollen viability, meiotic behavior, and production. Plants were grown in a climate chamber at 25-20 °C (day and night) and at a high temperature treatment 37-26 °C (day and night) from the vegetative (V4) development stage to physiological maturity. The experimental design was 2 × 12 factorial arrangement with six replications and the factors consisted of heat treatments and genotypes. In three replications, the number of newly opened flowers was checked daily. At physiological maturity, the following traits were evaluated: percentage of pod set, number of pods, number of viable seeds, number of aborted seeds, 100 seed weight, and seed yield (g per plant). The other three replications were used to collect flowers to create slides to study viability of the pollen grain and analyze the meiotic behavior. The heat treatment factor significantly affected the following traits: total number of pollen grains, number of flowers, number of pods, pod set, number of viable seeds, 100 seed weight, and seed yield. The raised temperature reduced these variables, except for percentage of pod set, and increased meiotic irregularities. The mean values regarding seed yield were 16.39 g per plant for the control treatment and 7.46 g per plant under high temperature. IAC Imperador, FT Nobre, Pérola, BRS Estilo, and IAC Diplomata stood out for higher bean seed yield under increased temperature.

Introduction

In Latin America and in Africa, dry bean (Phaseolus vulgaris L.) production is highly vulnerable to the effects of climate change, mainly higher temperatures and drought. Recent studies on climate modeling suggest that over the next decades, higher temperature will be the main threat to bean production with possible drastic reductions in planted area by 2050 (CGIAR, 2015).

Various research groups have evaluated the response of different species to high temperature. Hatfield and Prueger (2015) emphasize that the effect of extreme temperatures on plant development has not been treated as the main effect during the pollination phase and that plants exposure to heat in this phase has considerable impact on yield for all plant species. Ofir et al. (1993) studied six bean cultivars and observed a reduction in number of pods and seeds under exposure to 32/27 °C (day/night). The authors reported that yield reduction was caused by abscission of flower buds, flowers, and newly formed pods and by failure to fertilize. Monterroso and Wien (1990) also verified that the pre-fertilization period is more sensitive to heat stress, causing roughly 82 % of abscission of newly formed pods.

Omae et al. (2012) report that genotypic differences for tolerance to high temperature in bean are found in morphophysiological traits, such as partitioning, plant-water relations, photosynthetic and growth parameters of the shoots, which are related to reproductive responses. Heat tolerant cultivars normally have greater allocation of biomass to pods and greater pod set in the branches.

According to Ernest et al. (2017), heat-related yield loss in lima bean is partially due to reduction of the number of pollen grains released for fertilization. The effects of high temperature on production and release of pollen grains are determined by the conditions to which the flower is subject. Other factors, such as pollen viability and pollen tube growth can also play a role in response to heat stress.

In this context, this study investigated the effects of stress caused by high temperature on 12 bean genotypes, studying their reproductive biology through monitoring flower production, analysis of pollen grain viability, meiotic behavior, and pod set, as well as their yield potentials.