Genomewide analysis of the chitinase gene family in Populus trichocarpa

Abstract

The chitinase gene family is a large gene family in plants. As the first report of chitinase genes research on genome level in woody plants, here we report the identification of 37 Populus trichocarpa chitinase genes through a genomewide search. We divided these genes into five classes, based on sequence similarity and typical domain conservation. A strong correlation existed between gene structure and phylogeny, providing additional criteria to support classification. The distribution of chitinase genes on chromosomes was related to segmental duplications and tandem duplications revealing the expansion patterns of P. trichocarpa chitinase genes. As ubiquitous enzymes, chitinases are widely present in bacteria, fungi, animals and plants. They catalyse the hydrolytic cleavage of the β-1,4-glycosidic bonds between biopolymers N-acetyl-glucosamine residues from the chitin molecule which is a major structural component of fungal cell wall, exoskeleton of insects and crustacean shells (Cohen-Kupiec and Chet 1998). Plant chitinases act as defense proteins responding to pathogenic attack (Santos et al. 2008). They can play two different roles in defense mechanism against fungal pathogens. One is to degrade the fungal cell wall and inhibit fungal growth, the other is to let the fungal pathogens release small fragments that act as elicitors (Roldan Serrano et al. 2007). Besides, a lot of events in the growth and development processes such as pollination, seed germination and somatic embryogenesis cannot be completed without the participation of chitinases (Passarinho and de Vries 2002). So far, chitinase genes have been cloned and characterized from more than 20 plant species. It has been demonstrated that plant chitinase genes can be induced by various sources of stress such as elicitors, wounding, salicylic acid, plant hormones and fungal pathogens (Graham and Sticklen 1994).