E3 ligase BRG3 persulfidation delays tomato ripening by reducing ubiquitination of the repressor WRKY71

A regulatory mechanism involving persulfidation of E3 ligase BRG3 and repressor WRKY71 affects CYANOALANINE SYNTHASE1 transcription to delay ripening process in tomato. Hydrogen sulfide (H2S) is a gaseous signaling molecule reported to play multiple roles in fruit ripening. However, the molecular mechanisms underlying H2S-mediated delay in fruit ripening remain to be established. Here, the gene encoding a WRKY transcription factor, WRKY71, was identified as substantially upregulated in H2S-treated tomato (Solanum lycopersicum) via transcriptome profiling. The expression of WRKY71 was negatively associated with that of CYANOALANINE SYNTHASE1 (CAS1). Transient and stable genetic modification experiments disclosed that WRKY71 acts as a repressor of the tomato ripening process. CAS1 appears to play an opposite role, based on the finding that the ripening process was delayed in the cas1 mutant and accelerated in CAS1-OE tomatoes. Dual-luciferase reporter assay, yeast one-hybrid, electrophoretic mobility shift assay, and transient transformation experiments showed that WRKY71 bound to the CAS1 promoter and suppressed its activation. Moreover, the persulfidation of WRKY71 enhanced its binding ability to the CAS1 promoter. Data from luciferase complementation and Y2H assays confirmed that WRKY71 interacts with a BOI-related E3 ubiquitin-protein ligase 3 (BRG3) and is ubiquitinated in vitro. Further experiments showed that modification of BRG3 via persulfidation at Cys(206) and Cys(212) led to reduced ubiquitination activity. Our findings support a model whereby BRG3 undergoes persulfidation at Cys(206) and Cys(212), leading to reduced ubiquitination activity and decreased interactions with the WRKY71 transcript, with a subsequent increase in binding activity of the persulfidated WRKY71 to the CAS1 promoter, resulting in its transcriptional inhibition and thereby delayed ripening of tomatoes. Our collective findings provide insights into a mechanism of H2S-mediated regulation of tomato fruit ripening.

Automated summary

Through transcriptome profiling of tomatoes, it was found that WRKY71, a transcription factor, was significantly upregulated and negatively correlated with the delay in fruit ripening. Experimental evidence confirmed that WRKY71 acts as a repressor of tomato ripening, while CAS1 plays an opposite role. The interaction between WRKY71 and BRG3 is regulated by persulfidation, which affects the binding activity of WRKY71 to the CAS1 promoter.