Members of a New Group of Chitinase-Like Genes are Expressed Preferentially in Cotton Cells with Secondary Walls

Abstract

Two homologous cotton (Gossypium hirsutum L.) genes, GhCTL1 and GhCTL2, encode members of a new group of chitinase-like proteins (called the GhCTL group) that includes other proteins from two cotton species, Arabidopsis, rice, and pea. Members of the GhCTL group are assigned to family GH19 glycoside hydrolases along with numerous authentic chitinases (http://afmb.cnrs-mrs.fr/CAZY/index.html), but the proteins have novel consensus sequences in two regions that are essential for chitinase activity and that were previously thought to be conserved. Maximum parsimony phylogenetic analyses, as well as Neighbor-Joining distance analyses, of numerous chitinases confirmed that the GhCTL group is distinct. A molecular model of GhCTL2 (based on the three-dimensional structure of a barley chitinase) had changes in the catalytic site that are likely to abolish catalytic activity while retaining potential to bind chitin oligosaccharides. RNA blot analysis showed that members of the GhCTL group had preferential expression during secondary wall deposition in cotton lint fiber. Cotton transformed with a fusion of the GhCTL2 promoter to the beta -d-glucuronidase gene showed preferential reporter gene activity in numerous cells during secondary wall deposition. Together with evidence from other researchers that mutants in an Arabidopsis gene within the GhCTL group are cellulose-deficient with phenotypes indicative of altered primary cell walls, these data suggest that members of the GhCTL group of chitinase-like proteins are essential for cellulose synthesis in primary and secondary cell walls. However, the mechanism by which they act is more likely to involve binding of chitin oligosaccharides than catalysis.

CHITINASE-LIKE1/POM-POM1 and Its Homolog CTL2 Are Glucan-Interacting Proteins Important for Cellulose Biosynthesis in Arabidopsis

“…Several lines of evidence, including coexpression, phenotypic resemblance, and reduced cellulose content, have suggested a functional link between the cell wall CESAs and the CTLs (Hauser et al, 1995;Zhong et al, 2002;Mouille et al, 2003;Zhang et al, 2004). Using live-cell imaging, we found that mutations in CTL1 reduced the velocities of the primary wall CSCs (Figure 1; see Supplemental Movie 1 online), indicative of reduced cellulose deposition in the mutant cell walls ( Figure 1D).…”

“…However, CTL1 and CTL2 lack amino acids that are important for chitin binding and catalytic activity (Zhang et al, 2004).…”

“…The role of CTL1, and its close homolog CTL2, in cell wall biosynthesis is especially intriguing since associations between CTLs and primary or secondary cell wall synthesis have been reported in different plant species (Zhang et al, 2004). However, the biological function of the CTLs remains elusive.…”

Diverse chitinases are invoked during the activity-dormancy transition in spruce

“…The clustering of these genes with previously characterized chitinases from other species (Online Resource 6) and the presence or absence of a CBD suggests that Pg_GQ03206_D15.1 and Pg_GQ03803_J20.1 (cluster 1) are class IV chitinases; Pg_GQ0207_E09.1 (cluster 1) is a c l a s s V I I c h i t i n a s e ; P g G Q 0 1 8 3 _ A 0 6 . 2 a n d Pg_GQ03904_P01.1 (cluster 2) are class I chitinases; Pg_GQ03703_O09.1 and Pg_GQ03902_B01.1 (cluster 2) are class II chitinases; and Pg_GQ0046_J03.1 (cluster 3) is a class II chitinase or chitinase-like (CTL) sequence (sensu Zhang et al 2004;Sánchez-Rodríguez et al 2012).…”

“…Chitinases have been implicated in a variety of developmental processes like seed germination (Wu et al 2001), senescence (Hanfrey et al 1996), and morphogenesis (Zhang et al 2004), including somatic embryogenesis (Wiweger et al 2003;Johnsen et al 2005). There is increasing evidence that chitinases can mediate developmental processes through biosynthesis, assembly, and/or remodelling of various cell wall components Zhang et al 2004;Sánchez-Rodríguez et al 2012;Wu et al 2012).…”