Suppression of tryptophan synthase activates cotton immunity by triggering cell death via promoting SA synthesis

SUMMARY

Primary metabolism plays important roles in plant growth and development. However, the relationship between primary metabolism and adaptive immune response is largely unknown. Here, we employed RNA interference (RNAi), virus induced gene silencing (VIGS) technology, phytohormone profiling, genetic studies, and transcriptome and metabolome analysis to investigate the function of the tryptophan synthesis pathway in the resistance of cotton to V. dahliae. We find that knock -down of GbTSA1 (Tryptophan Synthase α) and GbTSB1 (Tryptophan Synthase β) induces a spontaneous cell death phenotype in a SA -dependent manner and enhance d resistance to V. dahliae in cotton plants . Metabolome analysis shows that indole and indolic metabolites are highly accumulated in GbTSA1 - or GbTSB1 - silenced plants. Transcriptomic analysis shows that exogenous indole promotes the expression level s of genes involved in SA synthesis and defense response. Similarly, indole application strongly enhances cotton resistance to V. dahliae. These results suggest that metabolic intermediates in the Trp synthesis pathway may be a signal to activate SA synthesis. T hese results also provide a strategy to elicit plant defense responses by the application of indole.