Low-temperature (LT) stress is a significant abiotic stress in rice growth, especially under direct seeding cultivation, where low temperatures can significantly affect seed germination and seedling growth of direct-seeded rice, thereby impacting the final yield of rice. In this study, we have identified a trehalose synthesis pathway gene, trehalose-6-phosphate phosphatase 3 (OsTPP3), involved in the regulation of low-temperature (LT) germination in rice, as well as its upstream regulatory factor, the ABA signaling pathway gene OsbZIP23. LT stress induced the accumulation of ABA by upregulating the expression of OsNCED3. Consistently, the overexpression of OsNCED3 significantly inhibited seed germination under LT. RT-qPCR experiments found that the expression of OsbZIP23 was also significantly induced under LT stress and ABA treatment. Overexpression of OsbZIP23 has increased the sensitivity to LT stress of rice seed, resembling the phenotype of OsNCED3 overexpressing seeds. Furthermore, both LT stress and exogenous ABA treatment increased the trehalose content in WT seeds by upregulating the expression of OsTPP3. Enhancing the expression of OsTPP3 or application of exogenous trehalose have significantly increased the sensitivity to LT stress during seed germination. Transcriptional activation and yeast one-hybrid assays demonstrated that OsbZIP23 bound to the promoter of OsTPP3 and activated its expression, which was intensified by LT stress or the application of ABA. Our study discovered an ABA-dependent OsbZIP23–OsTPP3 module that responds to LT stress, inhibiting seed germination under LT conditions by increasing trehalose accumulation, thus might balance the growth and stress resistance and provide a new insight into the genetic improvement of rice cultivars with better LT germination performance.

The chalcone isomerase gene OsCHI, one of the key genes in the flavonoid biosynthesis pathway, plays an important role in rice (Oryza sativa) resistance to abiotic stresses. This study reveals how the chalcone isomerase gene family member OsCHI3 participates in rice responses to drought stress through the regulation of flavonoid biosynthesis. Overexpression of OsCHI3 increased the tolerance of rice to drought stress. In contrast, CRISPR/Cas9-mediated deletion of OsCHI3 reduced the drought tolerance of rice, an effect that is reversed by exogenous ABA treatment. Transcriptomic and physiological biochemical analyses indicated that flavonoids regulated by OsCHI3 not only scavenge reactive oxygen species (ROS) but also increase drought tolerance in rice by stimulating ABA biosynthesis through the regulation of OsNCED1 and OsABA8ox3 expression. These findings demonstrate that OsCHI3 increases drought stress tolerance in rice by activating the antioxidant defense system and the ABA metabolic pathway, providing new clues for drought-resistant rice breeding research.

Filament-like plant proteins are intermediate filament proteins that play a major role in the development and growth of plants. However, no studies have systematically identified or characterized the filament-like plant proteins (FPP) family in plants. Fifty-nine FPP candidates were found in this study by analyzing the genomes of two dicots and four monocots. Phylogenetic analysis and multicollinearity mapping showed the relatively conserved evolution of FPP genes in monocots. In rice, eight OsFPPs were characterized and found to be induced or repressed by abiotic stresses. Additional genetic evidence showed that OsFPP7-overexpressing rice exhibited increased sensitivity to abscisic acid during the germination stage, disrupted Na⁺/K⁺ homeostasis, and disrupted balance of reactive oxygen species during the seedling stage when exposed to salt stress. Conversely, the knockout of OsFPP7 alleviated abscisic acid (ABA) sensitivity, safeguarded the antioxidant system and sodium ion transport system, and thus enhanced rice salt tolerance. In the cytoskeleton, the functions of FPPs in controlling salt stress and plant stress tolerance mechanisms are all further elucidated by our findings.

Root architecture development, an agronomic trait that influences crop yield, is regulated by multiple plant hormones. Abscisic acid (ABA) is a stress hormone that responds to multiple stresses, including salt, drought, and cold stress, and modulates various aspects of plant growth and development. In recent years, it has been found that ABA synthesized under mild stress or well-watered conditions can support plant growth and stress resistance by positively regulating root architecture development. In this review, we summarize the molecular, cellular, and organismal basis of ABA homeostasis in the root and how ABA signaling affects root architecture development both as an inhibitor and as an activator. We discuss the implications of these studies and the potential for exploiting the components of ABA signaling in designing crop plants with improved root system development and stress resistance.

The grain filling of inferior spikelets is much less complete than that of superior spikelets in rice cultivars with large panicles and numerous spikelets and is promoted by moderate soil drying (MD) post-anthesis. A growing body of evidence has shown that microRNAs function in regulating grain development. However, little is known about the mechanism of microRNA control of grain filling of inferior spikelets in response to MD. In this study, grain filling of inferior spikelets was promoted by MD treatment in Nipponbare. Small-RNA profiling at the most active grain-filling stage was conducted in inferior spikelets under control (CK) and MD treatment. Of 521 known and 128 novel miRNAs, 38 known and 9 novel miRNAs were differentially expressed between the CK and MD treatments. Target genes of differentially expressed miRNAs were involved in multiple developmental and signaling pathways associated with catalytic activity, carbohydrate metabolism, and other functions. Both miR1861 and miR397 were upregulated by MD, leading to a decrease in OsSBDCP1 and OsLAC, two negative regulators of SSIIIa activity and BR signaling, respectively. In contrast, miR1432 abundance was reduced by MD, resulting in upregulation of OsACOT and thus an elevated content of both ABA and IAA. These results suggest that both starch synthesis and phytohormone biosynthesis are regulated by differentially expressed miRNAs in inferior spikelets in response to MD treatment. Our results suggest the molecular mechanisms by which miRNAs regulate grain filling in inferior spikelets of rice under moderate soil drying, providing potential application in agriculture to increase rice yields by genetic approaches.