Role of the tomato fruit ripening regulator MADS-RIN in resistance to Botrytis cinerea infection.

Tomato MADS-RIN (RIN) transcription factor has been shown to be a master activator regulating fruit ripening. Recent studies have revealed that in addition to activating many other cell wall genes, it also represses expression of XTH5 , XTH8 , and MAN4a , which are positively related to excess flesh softening and cell wall degradation, which might indicate it has a potential role in pathogen resistance of ripening fruit. In this study, both wild-type (WT) and RIN-knockout (RIN-KO) mutant tomato fruit were infected with Botrytis cinerea to investigate the function of RIN in defense against pathogen infection during ripening. The results showed that RIN-KO fruit were much more sensitive to B. cinerea infection with larger lesion sizes. Transcriptome data and qRT-PCR assay indicate genes of phenylalanine ammonialyase (PAL) and chitinase (CHI) in RIN-KO fruit were reduced and their corresponding enzyme activities were decreased. Transcripts of genes encoding pathogenesis-related proteins (PRs), including PR1a , PRSTH2 , and APETALA2/Ethylene Response Factor (AP2/ERF) including ERF.A1 , Pti5 , Pti6 , ERF.A4 , were reduced in RIN-KO fruit compared to WT fruit. Moreover, in the absence of RIN the expression of genes encoding cell wall-modifying enzymes XTH5 , XTH8 , MAN4a has been reported to be elevated, which is potentially correlated with cell wall properties. When present, RIN represses transcription of XTH5 by activating ERF.F4 , a class II (repressor class) ERF gene family member, and ERF.F5. These results support the conclusion that RIN enhances ripening-related resistance to gray mold infection by upregulating pathogen-resistance genes and defense enzyme activities as well as reducing accumulation of transcripts encoding some cell wall enzymes. [ABSTRACT FROM AUTHOR]