Molecular Characterization Of DDB1 And Small Heat-shock-protein Gene HSP21.5A-mediated Signaling Pathway In Carotenoids Biosynthesis And Fruit Ripening In Tomato

Fruit ripening is a process governed by multiple external and internal cues and accompanied by changes in color,texture,volatiles and additional quality traits.While delayed ripening and increased phytonutrients are desired traits,delayed ripening is often accompanied by reduced nutritional value.The tomato hp1(ddb1)mutant has attracted attention for its phytonutrients over-accumulation.In this study,we show that the hp1 mutant also exhibits delayed fruit maturation and ripening initiation.Furthermore,mutation in DDB1 gene alters fruit size and impedes fruit softening.Transcriptome and proteome analysis of hp1 at various developmental stages suggested that DDB1 mutation influences fruit ripening through altering ripening-associated genes expression at both transcriptional and translational level.Ethylene is a critical plant hormone regulating fruit ripening and DDB1 mutation influences the expression of genes involved in ethylene biosynthesis and signaling pathway.A small heat-shock-protein HSP21.5A was found to be downregulated in hpl and it expresses at very low levels at early fruit develommental stages while dramatically increases at the onset of fruit ripening,exhibiting a ripening-related expression pattern.Suppression of HSP21.5A leads to alteration in timing of ripening initiation,fruit size,pigmentation,chlorophyll degradation and photomorphogenic responses.Transcriptome analysis of HSP21.5A RNAi lines showed that known ripening genes,including FUL2(FRUITFUL 2),HSP21 and SGR1 were downregulated in hp1 and HSP21.5A RNAi lines.Moreover,ABA-related genes including CYP707A2,PYL6 and ASR4 exhibited altered expression pattern in hp1 and HSP21.5A RNAi lines.Taken together,DDB1 and HSP21.5A influences fruit development and ripening process through regulation of complex gene network providing potential resource for increasing fruit nutritional value and delaying fruit softening simultaneously.