Populus chitinase genes: structure, organization, and similarity of translated sequences to herbaceous plant chitinases

Abstract

Poplar trees have at least two different chitinase genes, win6 and win8, which are systemically wound-inducible and belong to multigene families [Proc Natl Acad Sci USA 86: 7895-7899]. On one genomic clone that we have partially sequenced, there are three win6 genes which are transcriptionally oriented in the same direction. Between two of the win6 genes is a gene that we have designated chitinase X (chiX), which appears to be a pseudogene belonging to a multigene family distinct from win6 and win8. The win6 and chiX genes we have sequenced contain two AT-rich introns that correspond in location to those in a basic chitinase gene from tobacco. The predicted Win6 proteins have a putative signal peptide, a cysteine-rich 'hevein' domain, a hinge region, and a catalytic domain as described in Shinshi et al. [Plant Mol Biol 14: 357-368]. The predicted Win8 protein, by contrast, completely lacks a hinge region. Both Win6 and Win8 are expected to be highly acidic (with a calculated net charge of -15 to -17), whereas ChiX proteins are likely to be basic. Based on an inferred phylogeny, the catalytic domain of ChiX is more closely related to the basic chitinases of herbaceous plants than are either Win6 or Win8.