Identification of the SHINE clade of AP2/ERF domain transcription factors genes in Carica papaya; Their gene expression and their possible role in wax accumulation and water deficit stress tolerance in a wild and a commercial papaya genotypes

Abstract

Climate change has resulted in alterations in temperature, soil salinity and droughts in many parts of the world. Carica papaya is one of the most important tropical fruits worldwide, although it is considered as a tolerant crop, water deficit stress affects its production. The aim of the present work was first to identify genes of the SHINE clade of AP2/ERF domain in the genome of C. papaya also, to characterize and compare the physiological performance, the total content of waxes and the expression levels of genes involved in wax biosynthesis in two papaya genotypes of contrasting tolerance (Maradol and Yuc1), when exposed to water deficit stress. Two genes (CpSHN1 and CpSHN2) were identified in C. papaya. It was clear that under water deficit stress, Yuc1 (a wild genotype collected at its center of origin), accumulated more cuticular waxes and had higher expression of both CpSHN1 and CpSHN2 genes than Maradol. This increased wax content might partly contribute to the higher water-deficit stress tolerance observed in Yuc1. Our results suggest that in response to water-deficit stress, CpSHN genes are involved in wax biosynthesis in C. papaya, allowing the accumulation of waxes (particularly alkanes). Both genotypes, showed tolerance to water stress, however the ability of Yuc1 to upregulate stress tolerance related genes faster than Maradol, might have favored an increased amount of waxes in leaves, contributing partly to its greater water-deficit stress tolerance than its commercial counterpart Maradol. The expression levels of CpSHN1 increased 30-fold in Yuc1 in response to water deficits and this was correlated with its superior ability to accumulate waxes. Although more studies are needed to further evaluate the functionality of CpSHN in water-limiting environments, our results suggest that CpSHN1 might be a good candidate gene to increase the water-deficit stress tolerance of this important tropical species.