Heat stress and sexual reproduction in maize: unveiling the most pivotal factors and the greatest opportunities.

The escalation in the intensity, frequency, and duration of high-temperature (HT) stress is currently unparalleled, which aggravates the challenges for crop production. Yet, the stage-dependent responses of reproductive organs to HT stress at the morphological, physiological, and molecular levels remain inadequately explored in pivotal staple crops. This review synthesized current knowledge regarding the mechanisms by which HT stress induces abnormalities and aberrations in reproductive growth and development, as well as by which it alters the morphology and function of florets, flowering patterns, and the processes of pollination and fertilization in maize (Zea mays L.). We identified the stage-specific sensitivities to HT stress and accurately defined the sensitive period from a time scale of days to hours. The microspore tetrad phase of pollen development and anthesis (especially shortly after pollination) are most sensitive to HT stress, and even brief temperature spikes during these stages can lead to significant kernel loss. The impetuses behind the heat-induced impairments in seed set are closely related to carbon, reactive oxygen species, phytohormone signals, ion (e.g. Ca2+) homeostasis, plasma membrane structure and function, and others. Recent advances in understanding the genetic mechanisms underlying HT stress responses during maize sexual reproduction have been systematically summarized.

Anthropogenic land-use change decreases pollination and male and female fitness in terrestrial flowering plants.

BACKGROUND AND AIMS: The majority of the earth's land area is currently occupied by humans. Measuring how terrestrial plants reproduce in these pervasive environments is essential for understanding their long-term viability and their ability to adapt to changing environments. METHODS: We conducted hierarchical and phylogenetically-independent meta-analyses to assess the overall effects of anthropogenic land-use changes on pollination, and male and female fitness in terrestrial plants. KEY RESULTS: We found negative global effects of land use change (i.e., mainly habitat loss and fragmentation) on pollination and on female and male fitness of terrestrial flowering plants. Negative effects were stronger in plants with self-incompatibility (SI) systems and pollinated by invertebrates, regardless of life form and sexual expression. Pollination and female fitness of pollination generalist and specialist plants were similarly negatively affected by land-use change, whereas male fitness of specialist plants showed no effects. CONCLUSIONS: Our findings indicate that angiosperm populations remaining in fragmented habitats negatively affect pollination, and female and male fitness, which will likely decrease the recruitment, survival, and long-term viability of plant populations remaining in fragmented landscapes. We underline the main current gaps of knowledge for future research agendas and call out not only for a decrease in the current rates of land-use changes across the world but also to embark on active restoration efforts to increase the area and connectivity of remaining natural habitats.

Glucuronidation of type II arabinogalactan polysaccharides function in sexual reproduction of Arabidopsis.

Arabinogalactan proteins (AGPs) are complex, hyperglycosylated plant cell wall proteins with little known about the biological roles of their glycan moieties in sexual reproduction. Here, we report that GLCAT14A, GLCAT14B, and GLCAT14C, three enzymes responsible for the addition of glucuronic acid residues to AGPs, function in pollen development, polytubey block, and normal embryo development in Arabidopsis. Using biochemical and immunolabeling techniques, we demonstrated that the loss of function of the GLCAT14A, GLCAT14B, and GLCAT14C genes resulted in disorganization of the reticulate structure of the exine wall, abnormal development of the intine layer, and collapse of pollen grains in glcat14a/b and glcat14a/b/c mutants. Synchronous development between locules within the same anther was also lost in some glcat14a/b/c stamens. In addition, we observed excessive attraction of pollen tubes targeting glcat14a/b/c ovules, indicating that the polytubey block mechanism was compromised. Monosaccharide composition analysis revealed significant reductions in all sugars in glcat14a/b and glcat14a/b/c mutants except for arabinose and galactose, while immunolabeling showed decreased amounts of AGP sugar epitopes recognized by glcat14a/b and glcat14a/b/c mutants compared with the wild type. This work demonstrates the important roles that AG glucuronidation plays in Arabidopsis sexual reproduction and reproductive development.

Warming of experimental plant-pollinator communities advances phenologies, alters traits, reduces interactions and depresses reproduction.

Climate change may disrupt plant-pollinator mutualisms by generating phenological asynchronies and by altering traits that shape interaction costs and benefits. Our knowledge is limited to studies that manipulate only one partner or focus on either phenological or trait-based mismatches. We assembled communities of three annual plants and a solitary bee prior to flowering and emergence to test how springtime warming affects phenologies, traits, interactions and reproductive output. Warming advanced community-level flowering onset, peak and end but did not alter bee emergence. Warmed plant communities produced fewer and smaller flowers with less, more-concentrated nectar, reducing attractiveness, and warmed bees were more generalized in their foraging, reducing their effectiveness. Plant-bee interactions were less frequent, shorter and peaked earlier under warming. As a result, warmed plants produced fewer, lighter seeds, indicating pollinator-mediated fitness costs. Climate change will perturb plant-pollinator mutualisms, causing wide-ranging effects on partner species and diminishing the ecosystem service they provide.

Embryological observations on seed abortion in Hibiscus syriacus L. and physiological studies on nutrients, enzyme activity and endogenous hormones.

Under natural conditions, most Hibiscus syriacus L. individuals form very few mature seeds or the mature seeds that do form are of poor quality. As a result, seed yield is poor and seeds have low natural germinability. These phenomena strongly hinder utilization of the excellent germplasm resources of H. syriacus. The study has shown that pollen activity and stigma receptivity were high on the day of anthesis, and the pistils and stamens were fertile. Pollen release and stigma receptivity were synchronous. But in styles following self and cross-pollination, pollen tube abnormalities (distortion and twisting of the pollen tubes) and callose deposition were observed. Cross-pollinated pollen tubes elongated faster and fewer pollen tube abnormalities were observed compared with self-pollinated pollen tubes. And during embryo development, abnormalities during the heart-shaped embryo stage led to embryo abortion. Imbalance in antioxidant enzyme activities and low contents of auxin and cytokinin during early stages of embryo development may affect embryo development. Therefore, a low frequency of outcrossing and mid-development embryo abortion may be important developmental causes of H. syriacus seed abortion. Nutrient deficiencies, imbalance in antioxidant enzyme activities, and a high content of abscisic acid at advanced stages of seed development may be physiological causes of seed abortion.

Do Silene species with exposed stigmas tolerate interference by heterospecific pollen?

PREMISE: Co-flowering species that have not evolved an avoidance mechanism may have tolerance to heterospecific pollen (HP) deposition as an adaptive strategy to minimize any deleterious effects of HP transfer, but empirical evidence for the tolerance hypothesis remains scarce. METHODS: To estimate the potential effects of heterospecific pollen deposition (HPD) on female reproductive success, we counted conspecific (CP) and HP pollen grains deposited on stigmas and assessed subsequent seed set of both open- and hand-pollinated flowers in three co-flowering Silene species with exposed stigmas that usually received numerous HP grains on the elongated receptive area. RESULTS: The percentage of HP grains per flower (HP%) varied from 16.6% to 43.0% among three species. Silene chungtienensis had lower HP%, and the CP-HP relationship was neutral; S. gracilicaulis and S. yunnanensis had a relatively higher HP% with a positive CP-HP relationship. The effects of CP and HP number on natural seed set were positive for all three species, but HP% had stronger negative effects in S. chungtienensis and S. gracilicaulis. In hand-pollinated flowers of the three Silene species, seed set did not decrease with HP whether CP was in excess or insufficient, indicating no negative effects of HPD on seed production. CONCLUSIONS: Consistent with the tolerance hypothesis, our results indicated that species with higher HP interference are likely to be tolerant to an increase in HP%. These species with generalist-pollinated flowers and exposed large stigmas may benefit from an increase of conspecific pollen deposition, despite the associated increase in heterospecific pollen deposition.

Two aspartic proteases, BnaAP36s and BnaAP39s, regulate pollen tube guidance in Brassica napus.

Pollen tube (PT) growth towards the micropyle is critical for successful double fertilization. However, the mechanism of micropyle-directed PT growth is still unclear in Brassica napus. In this study, two aspartate proteases, BnaAP36s and BnaAP39s, were identified in B. napus. BnaAP36s and BnaAP39s were localized to the plasma membrane. The homologues of BnaAP36 and BnaAP39 were highly expressed in flower organs, especially in the anther. Sextuple and double mutants of BnaAP36s and BnaAP39s were then generated using CRISPR/Cas9 technology. Compared to WT, the seed-set of cr-bnaap36 and cr-bnaap39 mutants was reduced by 50% and 60%, respectively. The reduction in seed-set was also found when cr-bnaap36 and cr-bnaap39 were used as the female parent in a reciprocal cross assay. Like WT, cr-bnaap36 and cr-bnaap39 pollen were able to germinate and the relative PTs were able to elongate in style. Approximately 36% and 33% of cr-bnaap36 and cr-bnaap39 PTs, respectively, failed to grow towards the micropyle, indicating that BnaAP36s and BnaAP39s are essential for micropyle-directed PT growth. Furthermore, Alexander's staining showed that 10% of cr-bnaap39 pollen grains were aborted, but not cr-bnaap36, suggesting that BnaAP39s may also affect microspore development. These results suggest that BnaAP36s and BnaAP39s play a critical role in the growth of micropyle-directed PTs in B. napus. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-023-01377-1.

Self-incompatibility: a targeted, unexplored pre-fertilization barrier in flower crops of Asteraceae.

Asteraceae (synonym as Compositae) is one of the largest angiosperm families among flowering plants comprising one-tenth of all agri-horticultural species grown across various habitats except in Antarctica. These are commercially utilized as cut and loose flowers as well as pot and bedding plants in landscape gardens due to their unique floral traits. Consequently, ineffective seed setting and presence of an intraspecific reproductive barrier known as self-incompatibility (SI) severely reduces the effectiveness of hybridization and self-fertilization by traditional crossing. There have been very few detailed studies of pollen-stigma interactions in this family. Moreover, about 63% of Aster species can barely self-fertilize due to self-incompatibility (SI). The chrysanthemum (Chrysanthemum × morifolium) is one of the most economically important ornamental plants in the Asteraceae family which hugely shows incompatibility. Reasons for the low fertility and reproductive capacity of species are still indefinite or not clear. Hence, the temporal pattern of inheritance of self-incompatibility and its effect on reproductive biology needs to be investigated further to improve the breeding efficiency. This review highlights the self-incompatible (SI) system operating in important Astraceous (ornamental) crops which are adversely affected by this mechanism along with different physiological and molecular techniques involved in breaking down self-incompatibility.

Histological studies on the relationship between the low seed set and abnormal embryo sacs in sweet potato, Ipomoea batatas (L.) Lam.

This study aimed to investigate the relationship between low seed set and abnormal embryo sacs lacking normal female organs, such as one egg cell, two assistant cells, and two polar nuclei, in Ipomoea trifida, which is closely related to sweet potato, and sweet potato cultivars and lines, through histological analysis of their ovaries on flowering day. Ovaries of diploid, tetraploid, and hexaploid lines of I. trifida each had four ovules, except for some hexaploid lines with five or six ovules. Almost all sweet potato cultivars and lines had four ovules per ovary, although some sib-cross lines had two or three ovules. The number of ovules per ovary did not have direct effects on low seed set. The frequency of abnormal embryo sac increased with polyploidy in I. trifida. However, it varied among different sweet potato cultivars and lines. Moreover, the variation in abnormal embryo sacs occurred at an earlier stage of gametogenesis (type A) in the tetraploid and hexaploid plants of I. trifida and sweet potato cultivars and lines. These findings suggest that the high frequency of abnormal embryo sacs is a primary cause of low seed set in sweet potato and that it is closely related to the decline in seed propagation that occurs in the evolution process of sweet potato.

Fire influences reproductive outcomes by modifying flowering phenology and mate-availability.

A recent study posited that fire in grasslands promotes persistence of plant species by improving mating opportunities and reproductive outcomes. We devised an investigation to test these predicted mechanisms in two widespread, long-lived perennials. We expect fire to synchronize flowering, increase mating and boost seed set. We quantified individual flowering phenology and seed set of Liatris aspera and Solidago speciosa for 3 yr on a preserve in Minnesota, USA. The preserve comprises two management units burned on alternating years, allowing for comparisons between plants in burned and unburned areas within the same year, and plants in the same area across years with and without burns. Fire increased flowering synchrony and increased time between start date and peak flowering. Individuals of both species that initiated flowering later in the season had higher seed set. Fire was associated with substantially higher flowering rates and seed set in L. aspera but not S. speciosa. In L. aspera, greater synchrony was associated with increased mean seed set. Although fire affected flowering phenology in both species, reproductive success improved only in the species in which fire also synchronized among-year flowering. Our results support the hypothesis that reproduction in some grassland species benefits from fire.

Temporal skewness of pollination success in the spring ephemeral Trillium camschatcense.

Phenological overlap with pollinators is crucial for reproductive success in insect-pollinated plants. In this study, we examined whether pollinator visitation successfully occurred during an entire flowering season in two populations of the insect-pollinated spring ephemeral Trillium camschatcense in the Tokachi region of Hokkaido, northern Japan. We bagged flowers and excluded pollinator visitation during either the first or the last half of the entire flowering season to compare pollination success between the two periods. The two populations have experienced differing levels of climate warming in the last 60 years, which impacted pollinator visitation. In the population experiencing temperature rise more rapidly, fertilization rate and seed set decreased sharply when bagged during the first half period, indicating that pollinator visitation is skewed to the early part of the flowering season. The temporal skewness of pollination success would be an early warning signal of the impacts of climate warming on the reproductive success of T. camschatcense.

Comparative effects of pollen limitation, floral traits and pollinators on reproductive success of Hedysarum scoparium Fisch. et Mey. in different habitats.

BACKGROUND: Reproduction in most flowering plants may be limited because of the decreased visitation or activity of pollinators in fragmented habitats. Hedysarum scoparium Fisch. et Mey. is an arid region shrub with ecological importance. We explored the pollen limitation and seed set of Hedysarum scoparium in fragmented and restored environments, and examined whether pollen limitation is a significant limiting factor for seed set. We also compared floral traits and pollinator visitation between both habitats, and we determined the difference of floral traits and pollinators influenced reproductive success in Hedysarum scoparium. RESULTS: Our results indicated that supplementation with pollen significantly increased seed set per flower, which is pollen-limited in this species. Furthermore, there was greater seed set of the hand cross-pollination group in the restored habitat compared to the fragmented environment. More visits by Apis mellifera were recorded in the restored habitats, which may explain the difference in seed production between the fragmented and restored habitats. CONCLUSIONS: In this study, a positive association between pollinator visitation frequency and open flower number was observed. The findings of this study are important for experimentally quantifying the effects of floral traits and pollinators on plant reproductive success in different habitats.

Functional characterization of hydroxyproline-O-galactosyltransferases for Arabidopsis arabinogalactan-protein synthesis.

BACKGROUND: Arabinogalactan-proteins (AGPs) are structurally complex hydroxyproline-rich cell wall glycoproteins ubiquitous in the plant kingdom. AGPs biosynthesis involves a series of post-translational modifications including the addition of type II arabinogalactans to non-contiguous Hyp residues. To date, eight Hyp-galactosyltransferases (Hyp-GALTs; GALT2-GALT9) belonging to CAZy GT31, are known to catalyze the addition of the first galactose residues to AGP protein backbones and enable subsequent AGP glycosylation. The extent of genetic redundancy, however, remains to be elucidated for the Hyp-GALT gene family. RESULTS: To examine their gene redundancy and functions, we generated various multiple gene knock-outs, including a triple mutant (galt5 galt8 galt9), two quadruple mutants (galt2 galt5 galt7 galt8, galt2 galt5 galt7 galt9), and one quintuple mutant (galt2 galt5 galt7 galt8 galt9), and comprehensively examined their biochemical and physiological phenotypes. The key findings include: AGP precipitations with ß-Yariv reagent showed that GALT2, GALT5, GALT7, GALT8 and GALT9 act redundantly with respect to AGP glycosylation in cauline and rosette leaves, while the activity of GALT7, GALT8 and GALT9 dominate in the stem, silique and flowers. Monosaccharide composition analysis showed that galactose was decreased in the silique and root AGPs of the Hyp-GALT mutants. TEM analysis of 25789 quintuple mutant stems indicated cell wall defects coincident with the observed developmental and growth impairment in these Hyp-GALT mutants. Correlated with expression patterns, galt2, galt5, galt7, galt8, and galt9 display equal additive effects on insensitivity to ß-Yariv-induced growth inhibition, silique length, plant height, and pollen viability. Interestingly, galt7, galt8, and galt9 contributed more to primary root growth and root tip swelling under salt stress, whereas galt2 and galt5 played more important roles in seed morphology, germination defects and seed set. Pollen defects likely contributed to the reduced seed set in these mutants. CONCLUSION: Additive and pleiotropic effects of GALT2, GALT5, GALT7, GALT8 and GALT9 on vegetative and reproductive growth phenotypes were teased apart via generation of different combinations of Hyp-GALT knock-out mutants. Taken together, the generation of higher order Hyp-GALT mutants demonstrate the functional importance of AG polysaccharides decorating the AGPs with respect to various aspects of plant growth and development.

Greater reproductive assurance of asexual plant compared with sexual relative in a low-density sympatric population: Experimental evidence for pollen limitation.

High reproductive assurance is regarded as a key advantage of uniparentally reproducing organisms for establishing a new population. This demographic benefit should especially be relevant for plants with autonomous apomixis, that is those which produce seeds completely independently from mates and pollinators. Indeed, many autonomous apomicts occupy larger distributional ranges when compared to their sexual relatives, showing geographical parthenogenesis patterns. However, uniparental reproduction advantage has only rarely been quantified in natural populations and results provided a mixed support, partly because allopatric sexual and asexual populations were exposed to different environmental and pollination conditions causing considerable between-population variation in the level of reproductive assurance. Here, we compared the level and stability of reproductive assurance between sexual self-incompatible and asexual autonomously apomictic plants of Hieracium alpinum (Asteraceae) cultivated in a sympatric low-density population with two levels of spatial clumping of sexual plants. Overall, we found that the realized seed set (i.e. proportion of well-developed seeds per capitulum) of asexuals was ca. 3 times greater than that of sexuals (83% vs. 27%), whereas the variance of this trait expressed as coefficient of variation was ca. 4 times smaller in asexuals compared with sexuals (19% vs. 83%). Solitary sexual plants had more than 2 times lower realized seed set when compared to clumps composed of two spatially close (20-30 cm) sexual plants (13% vs. 34%). Our study provides experimental evidence for benefit of uniparental reproduction of asexuals in a sympatric situation when the availability of mates is limited. This, together with unpredictability of pollinator environment could provide autonomous apomicts with an ultimate demographic superiority during colonization reflected in geographical parthenogenesis observed in this species.

Causes and consequences of variation in heterospecific pollen receipt in Oenothera fruticosa.

PREMISE: Heterospecific pollen transfer, the transfer of pollen between species, is common among co-flowering plants, yet the amount of pollen received is extremely variable among species. Intraspecific variation in heterospecific pollen receipt can be even greater, but we lack an understanding of its causes and fitness consequences in wild populations. METHODS: We examined potential drivers of variation in heterospecific pollen receipt in Oenothera fruticosa. We evaluated the relationship between heterospecific and conspecific pollen receipt and considered how visitation by different pollinator groups, local floral neighborhood composition, and flowering phenology affect the total amount and proportion of heterospecific pollen received. Finally, we tested whether variation in heterospecific pollen receipt translated into lower seed production. RESULTS: Heterospecific pollen was ubiquitous on O. fruticosa stigmas, but the amount received was highly variable and unrelated to conspecific pollen receipt. Heterospecific pollen receipt depended on pollinator type, the proportion of nearby conspecific flowers, and flowering date. Significant interactions revealed that the effects of pollinator type and neighborhood were not independent, further contributing to variation in heterospecific pollen. Naturally occurring levels of heterospecific pollen were sufficient to negatively impact seed set, but large amounts of conspecific pollen counteracted this detrimental effect. CONCLUSIONS: Although selection could act on floral traits that attract quality pollinators and promote synchronous flowering in O. fruticosa, the risk of heterospecific pollen is equally dependent on local floral context. This work highlights how extrinsic and intrinsic factors contribute to intraspecific variation in heterospecific pollen receipt in wild plants, with significant fitness consequences.

Altitude and latitude have different effects on population characteristics of the widespread plant Anthyllis vulneraria.

Widespread plants may provide natural models for how population processes change with temperature and other environmental variables and how they may respond to global change. Similar changes in temperature can occur along altitudinal and latitudinal gradients, but hardly any study has compared the effects of the two types of gradients. We studied populations of Anthyllis vulneraria along a latitudinal gradient from Central Europe to the range limit in the North and an altitudinal gradient in the Alps from 500 m to the altitudinal limit at 2500 m, both encompassing a change in annual mean temperature of c. 11.5 °C. Plant size and reproduction decreased, but plant density increased along both gradients, indicating higher recruitment and demographic compensation among vital rates. Our results support the view that demographic compensation may be common in widespread species in contrast to the predictions of the abundant centre model of biogeography. Variation in temperature along the gradients had the strongest effects on most population characteristics, followed by that in precipitation, solar radiation, and soil nutrients. The proportion of plants flowering, seed set and seed mass declined with latitude, while the large variation in these traits along the altitudinal gradient was not related to elevation and covarying environmental variables like annual mean temperature. This suggests that it will be more difficult to draw conclusions about the potential impacts of future climate warming on plant populations in mountains, because of the importance of small-scale variation in environmental conditions.

Effect of cryopreservation on pollen viability, fertility and morphology of different Psidium species.

Cryopreservation of pollen is a complementary conservation strategy and can be used for conserve the diversity in the genus Psidium. The present study aims to cryopreserve the pollen of Psidium species to overcome asynchronous flowering. The pollen of different Psidium species were germinated in vitro in an optimized medium of germination. In vitro/in vivo pollen viability assessment and SEM analysis were carried out to determine the changes after cryopreservation. The in vitro pollen viability was determined at monthly intervals starting from fresh pollen until six months of cryopreservation. The in vivo fertility tests were carried out by pollination using both fresh and cryopreserved pollen. The cryopreserved pollen showed in vitro germination ranging from 1.78% (in P. molle) to 81.67% (in "H 12-5") compared to fresh pollen (2.16% in P. molle to 86.08% in P. guineense). In vivo fertility was tested by controlled pollination using six-month-old cryopreserved pollen and it resulted in fruit setting ranged between 3.33% (P. cattleianum var. cattleianum) and 27.66% (P. chinensis) as compared to fresh pollen between 4.0% (P. cattleianum var. cattleianum) and 30.66% (P. chinensis). Seed set and germination was also recorded in all the crosses attempted using cryopreserved pollen. These in vitro and in vivo results indicated that cryopreservation is an effective technique for breeding and conserving the haploid gene pool in cryo genebank. Scanning Electron Microscopic studies of pollen revealed no significant variation in shape and size after cryopreservation when compared to fresh pollen.

Heat stress during flowering in cereals - effects and adaptation strategies.

Heat stress during flowering has differential impact on male and female reproductive organ viability leading to yield losses in field crops. Unlike flooded rice, dryland cereals such as sorghum, pearl millet and wheat have optimised their flower opening during cooler early morning or late evening hours to lower heat stress damage during flowering. Although previous studies have concluded that pollen viability determines seed set under heat stress, recent findings have revealed pearl millet and sorghum pistils to be equally sensitive to heat stress. Integrating flower opening time during cooler hours with increased pollen and pistil viability will overcome heat stress-induced damage during flowering under current and future hotter climatic conditions.

AtHSPR is involved in GA- and light intensity-mediated control of flowering time and seed set in Arabidopsis.

Flowering is a dynamic and synchronized process, the timing of which is finely tuned by various environmental signals. A T-DNA insertion mutant in Arabidopsis HEAT SHOCK PROTEIN-RELATED (AtHSPR) exhibited late-flowering phenotypes under both long-day (LD) and short-day (SD) conditions compared to the wild-type, while over-expression of AtHSPR promoted flowering. Exogenous application of gibberellin (GA) partially rescued the late-flowering mutant phenotype under both LD and SD conditions, suggesting that AtHSPR is involved in GA biosynthesis and/or the GA signaling that promotes flowering. Under SD or low-light conditions, the Athspr mutant exhibited late flowering together with reduced pollen viability and seed set, defective phenotypes that were partially rescued by GA treatment. qRT-PCR assays confirmed that GA biosynthetic genes were down-regulated, that GA catabolic genes were up-regulated, and that the levels of bioactive GA and its intermediates were decreased in Athspr under both SD and low-light/LD, further suggesting that AtHSPR could be involved in the GA pathway under SD and low-light conditions. Furthermore, AtHSPR interacted in vitro with OFP1 and KNAT5, which are transcriptional repressors of GA20ox1 in GA biosynthesis. Taken together, our findings demonstrate that AtHSPR plays a positive role in GA- and light intensity-mediated regulation of flowering and seed set.

High temperature susceptibility of sexual reproduction in crop plants.

Climate change-induced increases in the frequency of extreme weather events, particularly heatwaves, are a serious threat to crop productivity. The productivity of grain crops is dependent on the success of sexual reproduction, which is very sensitive to heat stress. Male gametophyte development has been identified as the most heat-vulnerable stage. This review outlines the susceptibility of the various stages of sexual reproduction in flowering plants from the time of floral transition to double fertilization. We summarize current knowledge concerning the molecular mechanisms underpinning the heat stress-induced aberrations and abnormalities at flowering, male reproductive development, female reproductive development, and fertilization. We highlight the stage-specific bottlenecks in sexual reproduction, which regulate seed set and final yields under high-temperature conditions, together with the outstanding research questions concerning genotypic and species-specific differences in thermotolerance observed in crops. This knowledge is essential for trait selection and genetic modification strategies for the development of heat-tolerant genotypes and high-temperature-resilient crops.