Chuang Yang, Anni Luo, Hai-Ping Lu, Seth Jon Davis, Jian-Xiang Liu

Sci Bull (Beijing); 2024 Jan 15; 69(1):59-71. doi: 10.1016/j.scib.2023.11.046.

Abstract

Rice (Oryza sativa L.) production is threatened by global warming associated with extreme high temperatures, and rice heat sensitivity is differed when stress occurs between daytime and nighttime. However, the underlying molecular mechanism are largely unknown. We show here that two glycine-rich RNA binding proteins, OsGRP3 and OsGRP162, are required for thermotolerance in rice, especially at nighttime. The rhythmic expression of OsGRP3/OsGRP162 peaks at midnight, and at these coincident times, is increased by heat stress. This is largely dependent on the evening complex component OsELF3-2. We next found that the double mutant of OsGRP3/OsGRP162 is strikingly more sensitive to heat stress in terms of survival rate and seed setting rate when comparing to the wild-type plants. Interestingly, the defect in thermotolerance is more evident when heat stress occurred in nighttime than that in daytime. Upon heat stress, the double mutant of OsGRP3/OsGRP162 displays globally reduced expression of heat-stress responsive genes, and increases of mRNA alternative splicing dominated by exon-skipping. This study thus reveals the important role of OsGRP3/OsGRP162 in thermotolerance in rice, and unravels the mechanism on how OsGRP3/OsGRP162 regulate thermotolerance in a diurnal manner.

See https://pubmed.ncbi.nlm.nih.gov/38044192/

Fig. 1. EC controls the rhythmically expression of OsGRP3 and OsGRP162 at high temperatures. (a, b) Up-regulation of OsGRP3/OsGRP162 (a) and down-regulation of OsELF3-2 (b) by heat stress at midnight. (c) Increased diurnal expression of OsGRP3/OsGRP162 at high temperatures in elf3-2 mutant plants. Seven-day-old wild-type (ZH11), mutant plants of OsELF3-1 (elf3-1) or OsELF3-2 (elf3-2) plants grown consistently at 29 °C were kept at 29 °C or transferred to 45 °C, and total seedlings were sampled every 6 h at indicated zeitgeber time (ZT, X-axis) for RT-qPCR analysis. Relative expression is the expression level of OsGRP3 or OsGRP162 or evening complex (EC) genes at different sampling time normalized to that at ZT 0 h at 29 °C, both of which were normalized to that of PP2A. n = 3. Open and closed bars given in each panel represent light and dark periods, respectively. (d) Effector-reporter assays. Schematic design for the effectors and reporters is shown in which OsLUX/OsEC2 driven by the CaMV 35S promoter are used as the effectors, and the CaMV 35S constitutive promoter linked with a native or mutated form (m) of LBS sequence derived from the OsGRP3/OsGRP162 promoter was used as a reporter. Renilla luciferase driven by the CaMV 35S promoter in the same reporter vector was used as an internal control. Different combination of vectors was transiently expressed in tobacco leaves. Relative luciferase activity is the firefly luciferase activity normalized to the Renilla luciferase activity, which was then normalized to the empty vector control (MYC). n = 5 leaf discs. Different letters above the bars indicate significant differences for comparisons between two groups as determined by analysis of variance (ANOVA) with Tukey’s honestly significant difference (HSD) test (P < 0.05), and the same letters indicate no significant differences between two groups. Error bars depict standard error (SE).