Characterization of the SR/CAMTA Gene Family In Tomato: Cloning, Gene Expression, and Calcium Regulation

Nearly a quarter of all fresh fruits and vegetables in the U.S. market are lost after harvest due to damages caused by wounding, low temperature and pathogens, as well as fruit softening caused by the gaseous ethylene. The relationship of calcium to postharvest maladies is well known.  However, the underlying molecular mechanisms of calcium beneficial effects remain unclear. Previous studies indicated that a calcium/calmodulin-regulated SR/CAMTA gene family in Arabidopsis plays an important role in disease resistance, cold sensitivity and wounding response. To better understand the SR/CAMTA’s role in fruit ripening, we cloned seven SlSRs from tomato (Solanum lycopersicum L.). qRT-PCR analysis indicated that all SlSRs were highly and yet differentially expressed during fruit development. Interestingly, expression of SlSR2 was scarcely detected at the mature green stage (MG), the critical stage when fruit ripening is initiated. Expression of SlSR3L is essentially fruit specific. Treatment of MG fruits with ethylene, wounding or low temperature differentially affected expression of all SlSRs. SlSR2 was induced by all of these treatments, while other SlSRs exhibited varied responses to different treatments. A gel-mobility shift assay revealed that calmodulin was specifically bound to a predicted amphiphilic a-helix region of SlSRs in the presence of calcium.  Further functional analysis of tomato SlSRs may help in understanding the mechanisms of fruit ripening and senescence. The goal of this work is to better maintain tomato fruit quality and extend fruit shelf life.