Identification and functional analysis of germin-like protein Gene family in tea plant (Camellia sinensis)

Germins and germin-like proteins (GLPs) are ubiquitious glycoproteins in the plant kingdom. They play critical roles in both plant development and responses to stresses. Here we report the identification and functional characterization of the GLP gene family in tea plant (Camellia sinensis). By mining the leaf transcriptomes of tea plants, eight genes encoding GLPs were identified, they were designated as CsGLP1-8. Phylogenetic analysis placed the eight CsGLPs into three subfamilies, with CsGLP4 and CsGLP3 in the subfamily I and II, respectively and all the rest in subfamily III. The functions of CsGLPs were further characterized at both biochemical and biological levels. Analysis of recombinant proteins produced by expressing full-length cDNAs of individual CsGLPs in E. coli revealed that all CsGLPs had oxalate oxidase (OxO) or superoxide dismutase (SOD) activities, which are considered as typical biochemical characteristics of GLPs. In addition, expression analysis of individual CsGLP genes during bud sprouting as well as under biotic and abiotic stresses further confirmed their involvements in tea plant development and stress response. In apical buds, CsGLP genes exhibited differential response to phenological changes. CsGLP2 increased more extremely at bud sprouting stage than dormant stage compared with other genes, signifying its potentiality as a bud germination marker for the selection of germplasms in tea breeding. Under drought and H2O2 stresses, the expression levels of CsGLP almost constantly down-regulated, suggesting that bud sprouting was suppressed by water shortage and oxidative stress. For biotic treatment, six genes showed obvious positive response to herbivore-induced damage. Especially, CsGLP1 and CsGLP2 were dramatically induced by geometrid feeding, indicating that these two GLP members may be involved in insect resistance in tea plant. The results of this study will help to better understand the function of GLPs family in tea plants and to further exploit this knowledge for tea breeding.