A Non-Climacteric Fruit Gene <i>CaMADS-RIN</i> Regulates Fruit Ripening and Ethylene Biosynthesis in Climacteric Fruit

<div><p>MADS-box genes have been reported to play a major role in the molecular circuit of developmental regulation. Especially, <i>SEPALLATA</i> (<i>SEP</i>) 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 <i>SEP</i> genes to non-climacteric fruits ripening are still unclear. Here a <i>SEP</i> gene of pepper, <i>CaMADS-RIN</i>, has been cloned and exhibited elevated expression at the onset of ripening of pepper. To further explore the function of <i>CaMADS-RIN</i>, an overexpressed construct was created and transformed into <i>ripening inhibitor</i> (<i>rin</i>) mutant tomato plants. Broad ripening phenotypes were observed in <i>CaMADS-RIN</i> overexpressed <i>rin</i> fruits. The accumulation of carotenoid and expression of <i>PDS</i> and <i>ZDS</i> were enhanced in overexpressed fruits compared with <i>rin</i> mutant. The transcripts of cell wall metabolism genes (<i>PG</i>, <i>EXP1</i> and <i>TBG4</i>) and lipoxygenase genes (<i>TomloxB</i> and <i>TomloxC</i>) accumulated more abundant compared to <i>rin</i> mutant. Besides, both ethylene-dependent genes including <i>ACS2</i>, <i>ACO1</i>, <i>E4</i> and <i>E8</i> and ethylene-independent genes such as <i>HDC</i> and <i>Nor</i> were also up-regulated in transgenic fruits at different levels. Moreover, transgenic fruits showed approximately 1–3 times increase in ethylene production compared with <i>rin</i> 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 <i>CaMADS-RIN</i> 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 <i>SEP</i> genes in ripening of non-climacteric fruits.</p>