Structure and allele-specific expression variation of novel α/β hydrolase fold proteins in gentian plants

Previously, we identified two closely related proteins termed W14 and W15 that were enriched in the overwinter buds of the gentian plant Gentiana triflora. Expression of the latter protein W15 has been implicated in its association with cold hardiness, because of its absence in a cold-sensitive mutant. Here, we characterized these two proteins and the genes encoding them. Amino acid sequences of the W14 and W15 proteins showed difference at only three amino acid positions, and both of them showed homologies to alpha/beta hydrolase fold superfamily. Consistently, GST-fused W14 and W15 proteins expressed in bacteria showed hydrolase activity toward 1-naphtyl acetate. Structural analysis of these two genes in seven different gentian strains/cultivars including an anther culture-derived homozygous diploid revealed that W14 and W15 genes are allelic. Three genotypes were found; two strains carried both alleles (W14/W15), one carried the W15 genes in both alleles (W15/W15), and others were homozygous of W14 (W14/W14). Interestingly, expression of the two proteins exhibited allele-specificity. In one W14/W15 strain, expression of the W15 allele was almost repressed. In addition, organ specific expression of the alleles was observed in different cultivars. These observations were discussed in relation to winter hardiness of the gentian plants.