SNAC4 and SNAC9 transcription factors show contrasting effects on tomato carotenoids biosynthesis and softening

Color change due to lycopene accumulation and decreasing mu-xanthophyll and chlorophyll concentrations occurs during ripening of tomatoes (Solanum lycopersicum). The functions of the transcription factors SNAC4 (SINAC48, Accession number: NM 001,279,348.2) and SNAC9 (SINAC19, Accession number: XM 004,236,996.2) during ripening have been studied using virus-induced gene silencing (VIGS) to obtain SNACs-silenced fruit. Silencing of SNACs led to delayed ripening associated with reduced ethylene production, lycopene accumulation, and yellow or orange fruit. Genes involved in carotenoid pathway flux and ethylene biosynthesis were consistently downregulated. Silencing of SNAC4/9 altered tomato ripening processing. In SNAC4-silenced fruit, softening-related factors were down-regulated and there was less ABA (abscisic acid) than the negative control, whereas SNAC9-slilenced fruit showed an opposite phenotype. Exogenous ABA accelerated softening of SNAC4-silenced fruit, while exogenous nordihydroguaiaretic acid (NDGA) slowed down the softening of SNAC9-silenced fruit. Our results suggest that pathways dependent on ethylene and ABA are regulated by SNAC4 and SNAC9, respectively.