Early seed development events are highly sensitive to increased temperature. This high sensitivity to a short-duration temperature spike reduces seed viability and seed size at maturity. The molecular basis of heat stress sensitivity during early seed development is not known. We selected rice (Oryza sativa), a highly heat-sensitive species, to explore this phenomenon. Here, we elucidate the molecular pathways that contribute to the heat sensitivity of a critical developmental window during which the endosperm transitions from syncytium to the cellularization stage in young seeds. A transcriptomic comparison of seeds exposed to moderate (35°C) and severe (39°C) heat stress with control (28°C) seeds identified a set of putative imprinted genes, which were down-regulated under severe heat stress. Several type I MADS box genes specifically expressed during the syncytial stage were differentially regulated under moderate and severe heat stress. The suppression and overaccumulation of these genes are associated with precocious and delayed cellularization under moderate and severe stress, respectively. We show that modulating the expression of OsMADS87, one of the heat-sensitive, imprinted genes associated with syncytial stage endosperm, regulates rice seed size. Transgenic seeds deficient in OsMADS87 exhibit accelerated endosperm cellularization. These seeds also have lower sensitivity to a moderate heat stress in terms of seed size reduction compared with seeds from wild-type plants and plants overexpressing OsMADS87. Our findings suggest that OsMADS87 and several other genes identified in this study could be potential targets for improving the thermal resilience of rice during reproductive development.

The stomatal pores of plant leaves, situated in the epidermis and surrounded by a pair of guard cells, allow CO2 uptake for photosynthesis and water loss through transpiration. Blue light is one of the dominant environmental signals that control stomatal movements in leaves of plants in a natural environment. This blue light response is mediated by blue/UV A light-absorbing phototropins (phots) and cryptochromes (crys). Red/far-red light-absorbing phytochromes (phys) also play a role in the control of stomatal aperture. The signaling components that link the perception of light signals to the stomatal opening response are largely unknown. This review discusses a few newly discovered nuclear genes, their function with respect to the phot-, cry-, and phy-mediated signal transduction cascades, and possible involvement of circadian clock.

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Postzygotic reproductive isolation (RI) plays an important role in speciation. According to the stage at which it functions and the symptoms it displays, postzygotic RI can be called hybrid inviability, hybrid weakness or necrosis, hybrid sterility, or hybrid breakdown. In this review, we summarized new findings about hybrid incompatibilities in plants, most of which are from studies on Arabidopsis and rice. Recent progress suggests that hybrid incompatibility is a by-product of co-evolution either with “parasitic” selfish elements in the genome or with invasive microbes in the natural environment. We discuss the environmental influences on the expression of hybrid incompatibility and the possible effects of environment-dependent hybrid incompatibility on sympatric speciation. We also discuss the role of domestication on the evolution of hybrid incompatibilities.

A group of phylogenetically conserved nuclear factor Y transcription factors are preferentially expressed in the endosperm and probably play essential roles in endosperm development for rice and other monocots.

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SUMMARY LEAFY COTYLEDON1 (LEC1), a NUCLEAR FACTOR‐Y (NF‐Y) family member, plays a critical role in embryogenesis and seed development in Arabidopsis. Previous studies have shown that rice OsNF‐YB9 and OsNF‐YB7 are homologous to Arabidopsis LEC1. However, the functions of LEC1‐like genes in rice remain unclear. Here we report that OsNF‐YB9 and OsNF‐YB7 display sub‐functionalization in rice. We demonstrate that OsNF‐YB7 is expressed mainly in the embryo, whereas OsNF‐YB9 is preferentially expressed in the developing endosperm. Heterologous expression of either OsNF‐YB9 or OsNF‐YB7 in Arabidopsis lec1‐1 was able to complement the lec1‐1 defects. We failed to generate osnf‐yb7 homozygous mutants due to lethality caused by OsNF‐YB7 defects. Loss of OsNF‐YB9 function caused abnormal seed development: seeds were longer, narrower and thinner and exhibited a higher chalkiness ratio. Furthermore, the expression of genes related to starch synthesis was deregulated in osnf‐yb9. OsNF‐YB9 could interact with SPK, a sucrose synthase protein kinase that is predominantly expressed in rice endosperm. Knockout of SPK resulted in chalky seeds similar to those observed in the osnf‐yb9 mutants. Ectopic expression of OsNF‐YB9 in both rice and Arabidopsis resulted in unhealthy plants with small seeds. Taken together, these results suggest a critical role for OsNF‐YB9 in rice seed development.

Auxin is a phytohormone essential for plant development. However, our understanding of auxin-regulated endosperm development remains limited. Here, we described rice YUCCA (YUC) flavin-containing monooxygenase encoding gene OsYUC11 as a key contributor to auxin biosynthesis in rice (Oryza sativa) endosperm. Grain filling or storage product accumulation was halted by mutation of OsYUC11, but the deficiencies could be recovered by exogenous application of auxin. A rice transcription factor (TF) yeast library was screened, and 41 TFs that potentially bind to the OsYUC11 promoter were identified, of which OsNF-YB1, a member of the nuclear factor Y family, is predominantly expressed in the endosperm. Both osyuc11 and osnf-yb1 mutants exhibited reduced seed size and increased chalkiness, accompanied by a reduction in indole-3-acetic acid biosynthesis. OsNF-YB1 can bind the OsYUC11 promoter to induce gene expression in vivo. We also found that OsYUC11 was a dynamically imprinted gene that predominantly expressed the paternal allele in the endosperm up to 10 days after fertilization (DAF) but then became a non-imprinted gene at 15 DAF. A functional maternal allele of OsYUC11 was able to recover the paternal defects of this gene. Overall, the findings indicate that OsYUC11-mediated auxin biosynthesis is essential for endosperm development in rice.