Light, temperature, water, and fertilizer are arguably the most important environmental factors regulating crop growth and productivity. Environmental stimuli, including low light, extreme temperatures, and water stresses caused by climate change, affect crop growth and production and pose a growing threat to sustainable agriculture. Furthermore, soil salinity is another major environmental constraint affecting crop growth and threatening global food security. The grain filling stage is the final stage of growth and is also the most important stage in cereals, directly determining the grain weight and final yield. However, the grain filling process is extremely vulnerable to different environmental stimuli, especially for inferior spikelets. Given the importance of grain filling in cereals and the deterioration of environmental problems, understanding environmental stimuli and their effects on grain filling constitutes a major focus of crop research. In recent years, significant advances made in this field have led to a good description of the intricate mechanisms by which different environmental stimuli regulate grain filling, as well as approaches to adapt cereals to changing climate conditions and to give them better grain filling. In this review, the current environmental stimuli, their dose–response effect on grain filling, and the physiological and molecular mechanisms involved are discussed. Furthermore, what we can do to help cereal crops adapt to environmental stimuli is elaborated. Overall, we call for future research to delve deeper into the gene function-related research and the commercialization of gene-edited crops. Meanwhile, smart agriculture is the development trend of the future agriculture under environmental stimuli.

Salt stress has the most severe impact on plant growth and development, including seed germination. However, little is known about the mechanism of NR (nitrate reductase)-associated nitric oxide (NO) regulates salt tolerance during seed germination in rice. Herein, we shown that inhibition of seed germination by salt stress was significantly impaired by sodium nitroferricyanide (SNP), a NO donor. Then a triple mutant, nr1/nr2/nr3, was generated. Results shown that germination of triple mutants were delayed and were much more sensitive to salt stress than WT plant, which can be rescued by application of SNP. qPCR analysis revealed that expressions of abscisic acid (ABA) catabolism gene, OsABA8ox1, was suppressed in triple mutants under salt stress, resulting in an elevated ABA content. Similar to SNP, application of nitrate also rescued seed germination under salt stress, which, however, was blocked in the triple mutants. Further study revealed that a nitrate responsive transcript factor, OsNLP2, was induced by salt stress, which thus up-regulates the expression of OsNRs and NR activity, resulting in promoted salt tolerance during seed germination. In addition, nitrate-mediated salt tolerance was impaired in mutant of aba8ox1, a target gene for NLP2. Transient trans-activation assays further revealed NLP2 can significantly activate the expression of OsABA8ox1 and OsNR1, suggesting that NLP2 activates expression of ABA catabolism gene directly or indirectly via NR-associated NO. Taken together, our results demonstrate that NLP2-NR associated NO was involved in salt response by increasing ABA catabolism during seed germination and highlight the importance of NO for stress tolerance of plants.

Low temperature germination (LTG) is an important agronomic trait for direct-seeding cultivation of rice (Oryza sativa). Both OsMYB30 and OsTPP1 regulate the cold stress response in rice, but the function of OsMYB30 and OsTPP1 in regulating LTG and the underlying molecular mechanism remain unknown. Employing transcriptomics and functional studies revealed a sugar signaling pathway that regulates seed germination in response to low temperature. Expression of OsMYB30 and OsTPP1 was induced by low temperature during seed germination, and overexpressing either OsMYB30 or OsTPP1 delayed seed germination and increased sensitivity to low temperature during seed germination. Transcriptomics and qPCR revealed that expression of OsTPP1 was upregulated in OsMYB30-overexpressing lines but downregulated in OsMYB30-knockout lines. In vitro and in vivo experiments revealed that OsMYB30 bound to the promoter of OsTPP1 and regulated the abundance of OsTPP1 transcripts. Over accumulation of trehalose was found in both OsMYB30- and OsTPP1-overexpressing lines, resulting in inhibition of α-amylase 1a (OsAMY1a) gene during seed germination. Both low temperature and exogenous trehalose treatments suppressed the expression of OsAMY1a, and the osamy1a mutant was not sensitive to exogenous trehalose during seed germination. Overall, we concluded that OsMYB30 expression was induced by low temperature to activate the expression of OsTPP1 and increase trehalose content, which thus inhibited α-Amylase activity and seed germination. This study identified a phytohormone-independent pathway that integrates environmental cues with internal factors to control seed germination.

Soil salinity is a destructive environmental factor that inhibits plant growth and crop yield. Applying nitrogen fertilizer is a practical method to enhance salt tolerance. However, the underlying mechanisms remain largely unknown. Here, we demonstrated that NO3−-enhanced salt tolerance in rice (Oryza sativa L.) seedlings is mediated by nitrate reductase (NR)-dependent nitric oxide (NO) production. Seedlings grown in nitrate condition (N) exhibited much greater salt tolerance compared with those grown in ammonium nitrate and ammonium (A) conditions, a pattern also observed in the MADS-box transcription factor 27 (mads27) mutant. NR activity was highly induced by NO3− under both normal and salt stress conditions. Only the double mutant nr1/2 and the triple mutant nr1/2/3 displayed a dramatic reduction in salt tolerance. Application of tungstate suppressed salt tolerance of wild-type seedlings but not the triple mutants. Furthermore, both NO3−-enhanced salt tolerance and salt-induced NO production were totally blocked in triple mutants. However, treatment with exogenous sodium nitroprusside (an NO donor) significantly enhanced salt tolerance in both Nipponbare (NIP) and the triple mutants. Antioxidant enzyme activities in shoots were significantly inhibited in the triple mutants when compared with NIP. Furthermore, expression of OsAKT1 was specifically induced by NO3− but was inhibited in the roots of triple mutants, resulting in a lower potassium/sodium ratio in NR triple mutants. Our results revealed that NO3−-conferred salt tolerance is mediated by NR-dependent NO production in rice seedlings.

The seed, a critical organ in higher plants, serves as a primary determinant of agricultural productivity, with its quality directly influencing crop yield. Improper storage conditions can diminish seed vigor, adversely affecting seed germination and seedling establishment. Therefore, understanding the seed-aging process and exploring strategies to enhance seed-aging resistance are paramount. In this study, we observed that seed aging during storage leads to a decline in seed vigor and can coincide with the accumulation of hydrogen peroxide (H₂O₂) in the radicle, resulting in compromised or uneven germination and asynchronous seedling emergence. We identified the abscisic acid (ABA) catabolism gene, abscisic acid 8′-hydroxylase 2 (OsABA8ox2), as significantly induced by aging treatment. Interestingly, transgenic seeds overexpressing OsABA8ox2 exhibited reduced seed vigor, while gene knockout enhanced seed vigor, suggesting its role as a negative regulator. Similarly, seeds pretreated with ABA or diphenyleneiodonium chloride (DPI, an H₂O₂ inhibitor) showed increased resistance to aging, with more robust early seedling establishment. Both OsABA8ox2 mutant seeds and seeds pretreated with ABA or DPI displayed lower H₂O₂ content during aging treatment. Overall, our findings indicate that ABA mitigates rice seed aging by reducing H₂O₂ accumulation in the radicle. This study offers valuable germplasm resources and presents a novel approach to enhancing seed resistance against aging.