High-temperature stress suppresses allene oxide cyclase 2 and causes male sterility in cotton by disrupting jasmonic acid signaling

Cotton(Gossypium spp.) yield is reduced by stress. In this study, high temperature(HT) suppressed the expression of the jasmonic acid(JA) biosynthesis gene allene oxide cyclase 2(GhAOC2), reducing JA content and causing male sterility in the cotton HT-sensitive line H05. Anther sterility was reversed by exogenous application of methyl jasmonate(MeJA) to early buds. To elucidate the role of GhAOC2 in JA biosynthesis and identify its putative contribution to the anther response to HT, we created gene knockout cotton plants using the CRISPR/Cas9 system. Ghaoc2 mutant lines showed male-sterile flowers with reduced JA content in the anthers at the tetrad stage(TS), tapetum degradation stage(TDS), and anther dehiscence stage(ADS). Exogenous application of MeJA to early mutant buds(containing TS or TDS anthers) rescued the sterile pollen and indehiscent anther phenotypes, while ROS signals were reduced in ADS anthers. We propose that HT downregulates the expression of GhAOC2 in anthers, reducing JA biosynthesis and causing excessive ROS accumulation in anthers, leading to male sterility. These findings suggest exogenous JA application as a strategy for increasing male fertility in cotton under HT.

miR398b negatively regulates cotton immune responses to Verticillium dahliae via multiple targets

MicroRNAs(miRNAs)play essential roles in plant defense responses,although such roles have not been identified in cotton in response to the plant pathogenic fungus Verticillium dahliae.In this study,the functions of miR398b and its target genes in cotton-V.dahliae interaction were investigated.The transcript levels of miR398b were down-regulated by V.dahliae infection and miR398b overexpression in cotton made the plants more susceptible to V.dahliae.The results suggest that miR398b negatively regulates cotton resistance to V.dahliae.This may occur by miR398b repression of some CC-NBS-LRR genes via translational inhibition,interfering with defense responses and leading to cotton susceptibility to V.dahliae.Alternatively,miR398b may guide the cleavage of the mRNAs of GhCSD1,GhCSD2 and GhCCS,each of which functions in reactive oxygen species(ROS)regulation and homeostasis,thereby causing excessive ROS accumulation in miR398b-overexpressing plants in response to V.dahliae infection.This study suggests conserved and novel roles of miR398b in the cotton–V.dahliae interaction.These discoveries may be coupled with new strategies in cotton breeding programs to improve resistance to V.dahliae.