Heat stress (HS) has become one of the major abiotic stresses that severely constrain rice growth. Abscisic acid (ABA) plays an important role in plant development and stress response. However, the effect of different concentrations of exogenous ABA on HS tolerance in rice still needs to be further elucidated. Here, we found that high concentrations of exogenous ABA increased HS damage in seedlings, whereas 10⁻¹² M ABA treatment increased fresh and dry weight under HS relative to mock seedlings. Our further data showed that, in response to HS, 10⁻⁵ M, ABA-treated seedlings exhibited a lower chlorophyll content, as well as transcript levels of chlorophyll biosynthesis and antioxidant genes, and increased the accumulation of reactive oxygen species (ROS). In addition, the transcript abundance of some heat-, defense-, and ABA-related genes was downregulated on 10⁻⁵ M ABA-treated seedlings under HS. In conclusion, high concentrations of exogenous ABA reduced the HS tolerance of rice seedlings, and this negative effect could be achieved by regulating the accumulation of ROS, chlorophyll biosynthesis, and the transcription levels of key genes in seedlings under HS.

Brassinosteroids (BRs) are a crucial class of plant hormones that regulate many important agronomic traits in rice (Oryza sativa L.); thus, the BR signaling pathway is a very important tool for breeders to improve the grain yield and quantity of rice. Contrary to the well-established BR signaling pathway in Arabidopsis, there are significant gaps in the rice BR signaling pathway, especially the regulation mechanism from OsBSK3 to OsPPKLs and OsGSKs. In this study, we report how OsBSK3 knockout mutants confer shorter and lighter grains and exhibit a typical BR-insensitive phenotype, suggesting OsBSK3 plays a positive role in BR signaling without genetic redundancy with homologs. Furthermore, OsBSK3 could physically interact with OsPPKL1 and OsGSK3, the downstream components in BR signaling, as a scaffold protein, and inhibit the phosphatase activity of OsPPKL1 on the dephosphorylation of OsGSK3. In addition, the genetic evidence showed OsBSK3 acts upstream of OsPPKL1 in regulating grain length and weight. Our results clarify the role of OsBSK3 and provide new insights into BR-signaling mechanisms, leading to potential new targets for the genetic improvement of rice.

Rice sheath blight, caused by Rhizoctonia solani, is a major constraint on rice production, and its management still relies mainly on chemical fungicides. We evaluated the biocontrol agent Bacillus cereus AR156 against the disease and examined the transcriptional and biochemical changes in rice that accompany protection. AR156 achieved a biocontrol efficacy of 71.81% at 6 days after inoculation. RNA sequencing compared AR156-treated and control plants with and without pathogen challenge, and we identified 4554 and 2740 differentially expressed genes at 24 and 48 h after inoculation, respectively. AR156-responsive genes were enriched in secondary metabolism, plant-pathogen interaction, hormone signaling, phosphoinositide signaling, and membrane transport. Of the defense-associated DEGs, 97 TF/TRs and 86 predicted PRGs were shared between 24 and 48 h, most of which reversed their direction of change over time. Prominent TF/TR families included SNF2, bHLH, MYB, MYB-related, FAR1, PHD and WRKY, with KIN and RLK prominent among the predicted PRG classes. Quantitative RT-PCR and enzyme assays showed higher expression of several pathogenesis-related and hormone-associated markers, together with increased superoxide dismutase, peroxidase, and catalase activity after challenge. Together, these results indicate that AR156 suppresses rice sheath blight by temporally reshaping coordinated transcriptional and biochemical defenses rather than a single pathway.