Rice sl-MH-1 mutant induces cell death and confers blast resistance via the synergistic roles of signaling systems

Serotonin is ubiquitous across all forms of life and functions in responses to biotic and abiotic stresses. In rice, the conversion of tryptamine to serotonin is catalyzed by Sekiguchi lesion (SL). Previous studies have identified an sl mutation (a null mutation of SL) in several rice varieties and confirmed its increase of resistance and cell death. However, a systematic understanding of the reprogrammed cellular processes causing cell death and resistance is lacking. We performed a multi-omics analysis to clarify the fundamental mechanisms at the protein, gene transcript, and metabolite levels. We found that cell death and Magnaporthe oryzae (M. oryzae) infection of the sl-MH-1 mutant activated plant hormone signal transduction involving salicylic acid (SA), jasmonic acid (JA), and abscisic acid (ABA) in multiple regulatory layers. We characterized the dynamic changes of several key hormone levels during disease progression and under the cell death conditions and showed that SA and JA positively regulated rice cell death and disease resistance. SL-overexpressing lines confirmed that the sl-MH-1 mutant positively regulated rice resistance to M. oryzae. Our studies shed light on cell death and facilitate further mechanistic dissection of programmed cell death in rice.