Decrease in abscisic acid (ABA) to jasmonates (JAs) (ABA/JAs) ratio in lodicules induces glume unclosing of two-line hybrid rice grains under high temperature stress during anthesis

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● Heat stress during anthesis leads to glume-unclosing of grains of the two-line hybrid rice. ● Both abscisic acid and jasmonates regulate the glume-closing of the grain under heat stress. ● A higher ratio of abscisic acid to jasmonates and optimal levels of ABA and JAs contribute to reducing the glume-unclosing rate of grains. Glume unclosing induced by high-temperature (HT) stress during anthesis negatively affects the seed production and quality of two-line hybrid rice. ABA and JAs, including jasmonic acid (JA) and methyl jasmonate (MeJA), are essential hormones that mediate abiotic stress. However, the independent or synergistic mechanisms by which these hormones mediate glume unclosing remain poorly understood. Four photo-thermo-sensitive genic male sterile (PTSGMS) rice lines and their hybrids were pot-grown and subjected to HT stress during anthesis. The concentrations of ABA, JA, and MeJA in lodicules and their correlations with the rates of glume-opened (palea and lemma opened during anthesis), glume-closed (palea and lemma closed after opening), and glume-unclosed (palea and lemma failed to close after opening) spikelets were analyzed. The findings revealed that HT significantly reduced the ABA/JAs ratio in the lodicules and markedly increased the glume-unclosing rate after spikelet opening. Two-line hybrid rice with higher ABA/JAs ratios and appropriate levels of ABA and JAs in the lodicules under HT stress demonstrated lower rates of glume-unclosed spikelets. External application of 50 μmol L -1 ABA+10 μmol L -1 MeJA effectively decreased the glume-unclosing of spikelets and enhanced grain yield of two-line hybrid rice under HT stress. The results indicate that both ABA and JAs mediate glume closing of PTSGMS rice lines, and that an elevated ratio of ABA to JAs and appropriate contents of ABA and JAs contribute to reducing the glume-unclosing rate of two-line hybrid rice under HT stress.