Abstract
Auxin regulates flower and fruit abscission,but how developmental signals mediate auxin transport in abscission remains unclear.Here,we reveal the role of the transcription factor BEL1-LIKE HOMEO-DOMAIN11(SIBEL11)in regulating auxin transport during abscission in tomato(Solanum lyco-persicum).SIBEL11 is highly expressed in the fruit abscission zone,and its expression increases during fruit development.Knockdown of SIBEL11 expression by RNA interference(RNAi)caused premature fruit drop at the breaker(Br)and 3 d post-breaker(Br+3)stages of fruit development.Tran-scriptome and metabolome analysis of SIBEL11-RNAi lines revealed impaired flavonoid biosynthesis and decreased levels of most flavonoids,especially quercetin,which functions as an auxin transport inhibitor.This suggested that SIBEL11 prevents premature fruit abscission by modulating auxin ef-flux from fruits,which is crucial for the formation of an auxin response gradient.Indeed,quercetin treatment suppressed premature fruit drop in SIBEL11-RNAi plants.DNA affinity purification se-quencing(DAP-seq)analysis indicated that SIBEL11 induced expression of the transcription factor gene SIMYB111 by directly binding to its promoter.Chromatin immunoprecipitation-quantitative poly-merase chain reaction and electrophoretic mobility shift assay showed that S.lycopersicum MYELO-BLASTOSIS VIRAL ONCOGENE HOMOLOG111(SIMYB111)induces the expression of the core fla-vonoid biosynthesis genes SICHS1,SICHI,SIF3H,and SIFLS by directly binding to their promoters.Our findings suggest that the SIBEL11-SIMYB111 module modulates flavonoid biosynthesis to fine-tune auxin efflux from fruits and thus maintain an auxin response gradient in the pedicel,thereby preventing premature fruit drop.
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