Expression of FaXTH1 and FaXTH2 genes in strawberry fruit. Cloning of promoter regions and effect of plant growth regulators

Abstract

Xyloglucan endotransglycosylase/hydrolase (XTH) enzymes are involved in the remodeling of plant cell wall hemicelluloses. With the aim to study the involvement of XTHs in strawberry fruit ripening, two cDNAs (FaXTH1 and FaXTH2) coding putative XTH proteins were cloned and the expression level of both genes was analyzed on different plant tissues and during ripening of three cultivars that differ in fruit firmness: Camarosa and Selva (both firm cultivars) and Toyonoka (soft cultivar). Bioinformatics and phylogenetic analysis suggest that FaXTH1 would have xyloglucan endo-transglycosylase (XET) as exclusive activity, while FaXTH2 could be either a strict XET enzyme or have both XET/XEH (xyloglucan endo-hydrolase) activities. The expression profile of FaXTH1 was similar during ripening of the three cultivars analyzed; and a low transcript amount was detected in early ripening stages (LG and W) coinciding with a high diminution of fruit firmness. Nevertheless, the expression level of FaXTH1 was significantly higher during ripening in all stages in Camarosa and in LG, W and 100% R in Selva, in comparison to the softer cultivar (Toyonoka). On the other hand, not significant differences on FaXTH2 expression levels were detected during strawberry fruit ripening and between cultivars. These results suggest that FaXTH1 and FaXTH2 might play different roles on hemicellulose metabolism and fruit softening in strawberry. In addition, promoter regions of both genes were cloned and the effect of plant growth regulators on FaXTH1 and FaXTH2 gene expression was evaluated. FaXTH1 and FaXTH2 gene expression was significantly up-regulated when fruit were treated with gibberellic acid and abscisic acid, and when the endogenous source of auxins was removed. On the other hand, the expression of both genes decreased significantly in fruit treated with ethylene while the opposite situation was observed in fruit treated with 1-methylcyclopropene (1-MCP), an inhibitor of ethylene perception.