Defective mutations of SlSGR1, SlPSY1 and MYB12 genes lead to formation of green ripe fruit in tomato.

Modern tomatoes produce colourful mature fruits, but many wild tomato ancestors form green or gray green ripe fruits. In this study, tomato cultivar 'Lvbaoshi' (LBS) that produces green ripe fruits was found to contain three recessive loci that were responsible for development of green ripe fruits. The colourless peel of LBS fruits was caused by a 603-bp deletion in the promoter of SlMYB12. The candidate genes of the remaining two loci were identified as Stay-Green 1 (SlSGR1) and Phytoene Synthase 1 (SlPSY1). A single nucleotide substitution was present in sgr1 of LBS, resulting in disruption of mRNA splicing and truncation of the translated protein. A retrotransposon was found in the first exon of the psy1 locus in LBS, leading to the absence of any detectable PSY1 transcripts. Co-suppression of SGR1 and PSY1 by RNA interference (RNAi) converted the pink fruits into green ripe fruits in transgenic plants. An amino acid change in PSY1 and a deletion in the promoter of SGR1 were identified in many wild tomatoes bearing green or gray ripe fruits. Transgenic lines expressing ProSGR1::SGR1 from Solanum pennellii failed to convert the purple-flesh fruits into the red-flesh fruits. Overexpression of PSY1 from green ripe fruit wild tomatoes in LBS plants could only partially rescue the green ripe fruit phenotype of LBS. Downregulation of the Ripening Inhibitor (RIN) gene in the green-flesh (gf) plants led to development of green ripe fruits. This work uncovers a novel regulatory mechanism by which SlMYB12, SlPSY1 and SlSGR1 regulate fruit colour in cultivated tomatoes and some wild tomato species.