Fe deficiency-induced ethylene synthesis confers resistance to Botrytis cinerea.

Although iron (Fe) deficiency is an adverse condition to growth and development of plants, it increases the resistance to pathogens. It is still unclear how Fe deficiency induces the resistance to pathogens. Here, we reveal that the inoculation of Botrytis cinerea activates the Fe deficiency response of plants, which further induces ethylene synthesis and then resistance to B. cinerea. FIT and bHLH Ib are a pair of bHLH transcription factors which control the Fe deficiency response. Both the Fe deficiency-induced ethylene synthesis and resistance are blocked in fit-2 and bhlh4x-1 (a quadruple mutant for four bHLH Ib members). SAM1 and SAM2, two ethylene synthesis associated genes, are induced by Fe deficiency in a FIT-bHLH Ib dependent manner. Moreover, SAM1 and SAM2 are required for the increased ethylene and resistance to B. cinerea under Fe-deficient conditions. Our findings suggest that the FIT-bHLH Ib module activates the expression of SAM1 and SAM2, thereby inducing ethylene synthesis and resistance to B. cinerea. This study uncovers that the Fe signaling also functions as a part of the plant immune system against pathogens.