Abstract
MADS-box genes have been reported to play a major role in the molecular circuit of developmental regulation. Especially, SEPALLATA (SEP) group genes play a central role in the developmental regulation of ripening in both climacteric and non-climacteric fruits. However, the mechanisms underlying the regulation of SEP genes to non-climacteric fruits ripening are still unclear. Here a SEP gene of pepper, CaMADS-RIN, has been cloned and exhibited elevated expression at the onset of ripening of pepper. To further explore the function of CaMADS-RIN, an overexpressed construct was created and transformed into ripening inhibitor (rin) mutant tomato plants. Broad ripening phenotypes were observed in CaMADS-RIN overexpressed rin fruits. The accumulation of carotenoid and expression of PDS and ZDS were enhanced in overexpressed fruits compared with rin mutant. The transcripts of cell wall metabolism genes (PG, EXP1 and TBG4) and lipoxygenase genes (TomloxB and TomloxC) accumulated more abundant compared to rin mutant. Besides, both ethylene-dependent genes including ACS2, ACO1, E4 and E8 and ethylene-independent genes such as HDC and Nor were also up-regulated in transgenic fruits at different levels. Moreover, transgenic fruits showed approximately 1–3 times increase in ethylene production compared with rin mutant fruits. Yeast two-hybrid screen results indicated that CaMADS-RIN could interact with TAGL1, FUL1 and itself respectively as SlMADS-RIN did in vitro. These results suggest that CaMADS-RIN affects fruit ripening of tomato both in ethylene-dependent and ethylene-independent aspects, which will provide a set of significant data to explore the role of SEP genes in ripening of non-climacteric fruits.
Highlights
The ripening of fleshy fruit is a developmental biochemical process including numerous metabolic changes
Alignment analysis of amino acid sequences of MADS-box genes exhibited that CaMADS-RIN had conserved MADS-box domains (MADS domain, I domain and K domain) and its C-terminal region was highly divergent from other MADS-box sequences
Prior study showed that the expression of PSY1, PDS and ZDS was all reduced dramatically in rin mutant and the mutant fruits were green [12,34]
Summary
The ripening of fleshy fruit is a developmental biochemical process including numerous metabolic changes. These changes make fruit assisting in seed dispersal, and provide essential nutrition for human and animal diets [1,2,3]. While in non-climacteric fruits, such as strawberry (Fragaria 6 ananassa) and pepper (Capsicum annuum), these changes are not found [2]. These two distinct programs usually result in similar ripening-related changes, including changes in color, flavor, aroma and nutrition [1,2]
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