Chitinase genes in olive tree (Olea europaea L.): evolutionary dynamics and stress-responsive regulation

Chitinases (EC 3.2.1.14) are glycosyl hydrolases (GH) that break down glycosidic bonds in chitin. Plant chitinases are known to be implicated in responses to biotic and abiotic stresses, and particularly to defense against fungal pathogens by degrading fungal chitin. Olive tree (Olea europaea subsp. europaea) is a crucial fruit tree in Mediterranean ecosystems, but several pathogenic fungi can significantly affect production. The study of chitinase genes (OeChi) in olive tree can contribute to develop new strategies for a sustainable disease management.

A total of 28 chitinase genes and 5 chitinase-like genes (belonging to narbonin and SI-CPL domains) were found in the olive tree genome. Phylogenetic analysis clustered OeChi in two families (GH18 and GH19) and further into 5 classes, each one with its specificities regarding motifs and functional domains. It was observed that exon-intron structure was somewhat conserved in each group. Segmental and tandem duplication events were found for several GH18 genes, most of which appear to be under purifying selection. Expression profiling of OeChi genes under fungal infection revealed considerable variation among gene family members, with several genes showing strong induction. Promoter analysis identified a wide range of cis-regulatory elements associated with stress responses and hormone signaling pathways.

Collectively, our study improved knowledge on the olive tree chitinase gene family, thus providing a valuable foundation for future strategies aimed at improving fungal disease resistance in olive tree.