Drought is one of the major constraints to rice production worldwide. The development of rice panicle and spikelet meristem is repressed under the drought conditions, resulting in a reduction in the numbers of panicles and spikelets. In our recent report, we demonstrated that methyl jasmonate (MeJA) plays an important role in drought-induced loss of grain yield. Transgenic overexpression of the Arabidopsis gene jasmonic acid carboxyl methyltransferase (AtJMT) in rice resulted in a large reduction in grain yield through increased MeJA and ABA levels in young panicles. Exposure of nontransgenic plants to drought conditions also increased MeJA and ABA levels in young panicles and significantly reduced grain yield. In both cases, the reduction in grain yield was due to lower numbers of spikelets and lower filling rates than were observed for nontransgenic (NT) controls. The ABA increase in AtJMT transgenic panicles grown in non-drought conditions suggests that MeJA, rather than drought stress, induces ABA biosynthesis under drought conditions. These results led us postulate that plants produce MeJA during drought stress, which in turn stimulates the production of ABA, together leading to a loss of grain yield.
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