Long-distance transport of the phytohormone abscisic acid (ABA) has been studied for ~50 years, yet its mechanistic basis and biological significance remain very poorly understood. Here, we show that leaf-derived ABA controls rice seed development in a temperature-dependent manner and is regulated by defective grain-filling 1 (DG1), a multidrug and toxic compound extrusion transporter that effluxes ABA at nodes and rachilla. Specifically, ABA is biosynthesized in both WT and dg1 leaves, but only WT caryopses accumulate leaf-derived ABA. Our demonstration that leaf-derived ABA activates starch synthesis genes explains the incompletely filled and floury seed phenotypes in dg1. Both the DG1-mediated long-distance ABA transport efficiency and grain-filling phenotypes are temperature sensitive. Moreover, we extended these mechanistic insights to other cereals by observing similar grain-filling defects in a maize DG1 ortholog mutant. Our study demonstrates that rice uses a leaf-to-caryopsis ABA transport–based mechanism to ensure normal seed development in response to variable temperatures.

Leaf color affects the efficiency of photosynthesis, and leaf color mutants are important genetic materials for studying the mechanisms of photosynthesis, chlorophyll biosynthesis, and chloroplast development in rice. In this study, a white-striped leaf mutant, wst1, was obtained from the mutant population of the indica restorer line ‘Chuanhui 907’ (R907) when treated by ⁶⁰Co-γ radiation. Compared to the wild-type, the wst1 mutant showed normal leaf color before tillering and white stripes on the leaf and leaf sheaths after tillering. The chlorophyll and carotenoid contents were significantly reduced, and the thylakoids of chloroplasts developed abnormalities in wst1 plants in the tillering stage. The results of agronomic trait analysis showed that the number of effective panicles, plant height, seed setting rate, and 1000-grain weight of the wst1 mutant were significantly lower than those of the wild-type. Genetic analysis revealed that the phenotype of the wst1 mutant is controlled by a pair of recessive nuclear genes. The candidate gene was mapped to a 72 kb region between the InDel markers M6 and M12 on the short arm of chromosome 1 using molecular marker linkage analysis. Candidate genes were sequenced on the interval, and a G base was replaced by A at the 6972nd position on the 16th exon of LOC_Os01g01920, which encoded a previously reported protein containing the HD domain, WSF3/WFSL1, leading to alternative splicing, causing a 104 bp deletion in the coding region, and resulting in mistranslation after the 490 amino acid of the encoded protein translation in wst1. RT-qPCR analysis showed that the expression levels of most genes related to chlorophyll synthesis and chloroplast development were significantly altered in wst1 plants. Our study identified a novel allele of wsf3 and wfsl1 mutant and provided a new genetic resource and theoretical basis for further understanding of the molecular mechanism of WST1 gene regulation of white-striped leaves in rice.

Background: Male sterility is a critical trait for large-scale hybrid rice seed production, yet the genetic and molecular regulatory networks governing tapetal degradation during anther development remain incompletely understood. This study aimed to clone the causal gene underlying a novel rice non-pollen male sterility mutant and elucidate its role in tapetal development and microsporogenesis. Methods: The nms1 (non-pollen male sterility 1) sterile mutant was screened from the ethyl methanesulfonate (EMS)-mutagenized progeny of the elite indica restorer line Shuhui 498 (R498). Map-based cloning and whole-genome resequencing-assisted bulked segregant analysis were used to identify the causal variant. Gene function was verified via cytological observation, genetic complementation testing, RNA sequencing, and quantitative real-time PCR (qRT-PCR) to profile sterility-associated transcriptional changes. Results: Gene mapping identified a T635A single-nucleotide substitution within OsR498G0305626400.01 on chromosome 3, which encodes a strictosidine synthase-like protein. This nucleotide alteration causes a Val212Glu amino acid change and is associated with delayed tapetal degradation and pollen abortion. Transgenic complementation experiments verified that functional NMS1 restores fertility in nms1 mutant plants. Spatiotemporal expression analysis showed predominant NMS1 expression in late-developing spikelets. Furthermore, combined RNA sequencing and qRT-PCR analyses demonstrated that loss of NMS1 function leads to significant transcriptional dysregulation of key regulators of programmed cell death (PCD) in the tapetum (PTC2, TIP2) and pollen wall biosynthesis genes (TIP3, OsMS2). Conclusions: This study demonstrates that NMS1 plays a crucial role in coordinating tapetal degradation and microspore development in rice. The discovered functional SNP of NMS1 provides a novel theoretical foundation and a valuable sterile genetic resource for hybrid rice breeding.