ERF100 regulated by ERF28 and NOR controls pectate lyase 7, modulating fig (Ficus carica L.) fruit softening.

The mechanism regulating fruit textural changes has not been fully elucidated. Transcription factor FcERF100 showed rapid transcription repression during drastic texture loss in fig (Ficus carica L.) fruit ripening. Transient overexpression of FcERF100 delayed fig fruit softening and significantly decreased the transcript abundance of a key cell wall-modifying pectate lyase gene, FcPL7. Yeast one-hybrid (Y1H) assay, chromatin immunoprecipitation-qPCR, electrophoretic mobility shift assay (EMSA), and dual-luciferase reporter assay revealed that FcERF100 represses FcPL7 transcription by direct promoter binding via GCC-box and DRE/CRT elements. Stable transgenic fig lines further verified FcERF100's inhibitory effect on FcPL7 expression. We detected FcERF28 as an upstream element of FcERF100 by Y1H and EMSA, revealing its binding to, and activation of FcERF100 by dual-luciferase assay. Taken together, the FcERF28-FcERF100 transcriptional cascade serves as a synergistic flow-limiting valve for FcPL7 abundance. We then identified a NAC transcription factor, FcNOR, using FcERF100 as the bait by yeast two-hybrid screening. FcNOR silencing retarded fig fruit softening, with decreased FcPL7 transcript and pectate lyase activity. FcNOR interacted with FcERF100 to form a protein complex, attenuating FcERF100's transcriptional repression of FcPL7. Moreover, FcNOR bound directly to the promoter of FcERF100 and inhibited its transcription. In addition, ethylene treatment upregulated FcNOR and FcPL7 expression and downregulated FcERF28 and FcERF100 expression. Our findings reveal a novel FcERF100-centered regulatory complex and resolve how the complex achieves the necessary cell wall modification during an early stage of fruit growth and implements drastic softening at fruit ripening by modulating component proportions.