Characterization of Calmodulin Gene Family during Tomato Fruit Development and Ripening

Calmodulin, a calcium sensor, can recognize the different developmental and stress-triggered calcium changes. To investigate the function in fleshy fruit development and ripening, the expression of a family of six calmodulin genes (SlCaMs) were carried out. All calmodulins showed a double peak expression pattern. The first flat peak appeared at 10 to 30 days after anthesis. Then their expression declined to the basal level at mature green and breaker. Shortly after, a sharp and even higher peak appeared at turning/pink stages. SlCaMs showed different patterns in three ripening mutants rin, Nor and Nr. Furthermore SlCaMs, especially SlCaM2 were upregulated by ethylene. Transiently expressing SlCaM2 in mature green fruit delayed fruit ripening, whereas reducing SlCaM2 expression accelerated ripening. Thus SlCaMs could play double roles to regulate fruit ripening. Prior to the ethylene burst, the ethylene-independent repression of SlCaMs might be critical for fruit to initiate the ripening process. After the ethylene burst, SlCaMs could participate in the ethylene coordinated rapid ripening. In addition, all calmodulin genes at mature green stage were upregulated by salicylic acid and methyl jasmonate. Overexpression of SlCaM2 in tomato fruit enhanced resistance to Botrytis-induced decay, whereas reducing its expression resulted in increased lesion development. Calmodulin acts as a positive regulator of plant defense in fruit by activating defense pathways including salicylate- and jasmonate- signaling pathways, and SlCaM2 is the major calmodulin gene responsible for this event.