Members of a new group of chitinase-like genes are expressed preferentially in cotton cells with secondary walls.
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.
Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409, USA.
Deshui
D
Zhang
Maria
M
Hrmova
Chun-Hua
CH
Wan
Chunfa
C
Wu
Jace
J
Balzen
Wendy
W
Cai
Jing
J
Wang
Llewellyn D
LD
Densmore
Geoffrey B
GB
Fincher
Hong
H
Zhang
Candace H
CH
Haigler
D000595:Amino Acid Sequence; D015152:Blotting, Northern; D002473:Cell Wall / Q000235:genetics* / Q000378:metabolism; D002688:Chitinases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D005966:Glucuronidase / Q000235:genetics / Q000378:metabolism; D003368:Gossypium / Q000166:cytology / Q000235:genetics*; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
D018076:DNA, Complementary; D018744:DNA, Plant; D010940:Plant Proteins; D018749:RNA, Plant; D011993:Recombinant Fusion Proteins; C491153:CTL1 protein, Gossypium hirsutum; C491154:CTL2 protein, Gossypium hirsutum; D002688:Chitinases; D005966:Glucuronidase