Drought stress at jointing–booting directly affects plant growth and productivity in rice. Limited by natural factors, the jointing and booting stages of short-growth-period rice varieties are highly overlapped in high-latitude areas, which are more sensitive to water deficit. However, little is known about the dry matter translocation in rice and the strategies of starch synthesis and filling of superior and inferior grains under different drought stress was unclear. In this study, the rice plants were subjected to three degrees of drought stress (−10 kPa, −25 kPa, −40 kPa) for 15 days during the jointing–booting stage; we investigated dry matter accumulation and translocation, grain filling and enzyme activities to starch synthesis of superior and inferior grains in rice with overlapping growth stages from 2016 to 2017. The results showed that drought stress significantly reduced dry matter accumulation in the stems and leaves. Mild and moderate drought increased dry matter translocation efficiency. However, severe drought stress largely limited the dry matter accumulation and translocation. A large amount of dry matter remains in vegetative organs under severe drought stress. The high content in NSC in stem and sheath plays a key role in resisting drought stress. The drought stress at jointing–booting directly caused a change in the grain filling strategy. Under moderate and severe drought, the grain-filling active period of the superior grains was shortened to complete the necessary reproductive growth. The grain-filling active period of the inferior grains was significantly prolonged to avoid a decrease in grain yield. The significant decrease in the grain-filling rate of the superior and inferior grains caused a reduction in the thousand-grain weight. In particular, the influence of the grain-filling rate of inferior grains on the thousand-grain weight was more significant. Drought stress changed the starch synthesis strategies of the superior and inferior grains. Soluble starch synthase and starch branching enzyme activities of inferior grains increased significantly under drought stress. GBSS activity was not sensitive to drought stress. Therefore, amylose content was decreased and amylopectin synthesis was enhanced under drought stress, especially in inferior grains.

Water shortages and nitrogen (N) fertilizer overuse limit japonica rice production in Northeastern China. The interactions between water-saving irrigation and nitrogen management on rice root and shoot growth is still our research focus. Here, japonica rice (DN425) was subjected to the irrigation methods W1 (flooding irrigation), W2 [mild alternate wetting and drying irrigation (AWD); −10 kPa], W3 (severe AWD; −30 kPa), and different N fertilizer ratios were applied in different growth stages, namely, N1 (6:3:1:0), N2 (5:3:1:1), and N3 (4:3:2:1). From jointing to full heading stages, the highest photosynthate production capacity and root activity were obtained under W1N2. AWD markedly affected the root system and resulted in root senescence at later growth stages. Grain yield and N utilization efficiency were closely and positively correlated with the relative water content, crop growth rate (CGR), leaf area duration (LAD), the increase rate of root length density, root surface area density, and root volume density (RVD) from the jointing to full heading stages. This positive correlation was also observed in the increased rate of root bleeding sap (RBS) under W1N2 and CGR under W2N3. From full heading to maturity stages, N2 could promote root growth, LAD, and CGR under AWD to a greater extent than those under the other treatments. Water use efficiency (WUE) and N uptake efficiency (NUpE) were both negatively associated with the decreased rate of RVD, root dry weight (RDW), and RBS. They were closely and positively correlated with the increased rate of RDW and CGR. Our results suggested that W2N2 treatment delayed root senescence, maintained leaf photosynthesis, optimized the crop growth rate from full heading to maturity stages, and improved grain yield. The optimal grain yield, WUE, and NUpE were achieved at the irrigation water amount and topdressing fertilizer ratio of 41.40–50.34 × 102 and 31.20–34.83 kg ha–1, respectively.

Background Low-temperature chilling is a major abiotic stress leading to reduced rice yield and is a significant environmental threat to food security. Low-temperature chilling studies have focused on physiological changes or coding genes. However, ceRNA mechanism in rice at low temperatures has not been reported. Therefore, to establish the ceRNA network and elucidate the transcriptional regulatory network and physiological mechanism of rice leaves in response to low-temperature stress, experiments were conducted using two rice (Oryza sativa. L) varieties with significantly different cold tolerances. Results The cold-tolerant variety has prolonged and relatively stable regulation of antioxidant enzymes (superoxide dismutase [SOD] and peroxidase [POD] catalase [CAT], and total antioxidant capacity) and osmotic substances (Proline [PRO], Soluble sugars [SS], and Soluble protein [SP]), which can remove harmful substances to maintain plant cell stability. Further screening based on VIP (variable importance in the projection) identified SOD and POD as two of the most essential antioxidant phenotypes. Furthermore, by combining antioxidant physiological indices with whole transcriptome data through weighted gene co-expression network analysis (WGCNA), the highly correlated modules were black and green, significantly associated with critical antioxidant indices (SOD and POD). Enrichment analysis revealed that black module genes were significantly enriched in the redox pathway. This module hub gene included UDP-glucosyltransferase family protein (Os05g0527000), sesquiterpene synthase (Os08g0167800), indole-3-glycerophosphatase gene (Os03g0797500), encoding oxidoreductase gene (Os04g0339400), and unknown genes (Os05g0212900). The green module genes were significantly enriched in the linoleic acid metabolic pathway. This module hub gene included WRKY transcription factor (Os11g0685700),abscisic acid (ABA) signal transduction pathway-related gene plasma membrane hydrogen-ATPase (Os02g0825600), Beta-Ig-containing H3 structural domain protein leucine-rich repeat-like receptor kinase (Os02g0615800), and two unknown genes (Os03g0103950 and Os08g0288050). Therefore, we selected module hub and significantly enriched pathway genes to construct key competing endogenous ceRNA networks. Both modules’ networks were integrated to obtain the ceRNA network of six lncRNAs regulating three co-expressed mRNAs through four miRNAs and six lncRNAs regulating two co-expressed mRNAs through four miRNAs. Finally, we performed preliminary gene sequence difference analysis, subcellular localization, and phenotypic validation of mutants for the putative glutamate protein OsGLR1.2 (Os02g0787600), which was previously thought to be associated with Ca2+ transport. Conclusions The results of this study reveal the characteristics of the response of rice to low temperature and provide insight into the mechanisms of regulation of rice to low temperature.