Duplication of the class I cytosolic small heat shock protein gene and potential functional divergence revealed by sequence variations flanking the {alpha}-crystallin domain in the genus Rhododendron (Ericaceae).
OBJECTIVE
Positive selection in the -crystallin domain (ACD) of the chloroplast small heat shock protein (CPsHSP) gene was found in a previous study and was suggested to be related to the ecological adaptation of Rhododendron species in the subgenus Hymenanthes. Consequently, it was of interest to examine whether gene duplication and subsequent divergence have occurred in other sHSP genes, for example class I cytosolic sHSP genes (CT1sHSPs) in Rhododendron in Taiwan, where many endemic species have evolved as a result of habitat differentiation.


METHODS
A phylogeny of CT1sHSP amino acid sequences was built from Rhododendron, Arabidopsis thaliana, Oryza sativa, Populus trichocarpa, Vitis vinifera and other species for elucidation of the phylogenetic relationships among CT1sHSPs. Phylogenies of Rhododendron CT1sHSP nucleotide and amino acid sequences were generated for positive selection and functional divergence analysis, respectively. Positively selected sites and amino acid differences between types of Rhododendron CT1sHSPs were mapped onto the wheat sHSP16.9 protein structure. Average genetic distance (Dxy) and dN/dS ratios between types of Rhododendron CT1sHSP genes were analysed using sliding window analysis. Gene conversion was also assessed between types of Rhododendron CT1sHSPs.


RESULTS
Two types of Rhododendron CT1sHSP were identified. A high level of genetic similarity and diversity within and flanking the ACD, respectively, between types of Rhododendron CT1sHSP were found. Main differences between the two types of Rhododendron CT1sHSPs were: (1) increased hydrophobicity by two positively selected amino acid sites and a seven-amino-acid insertion in the N-terminal arm; and (2) increased structural flexibility and solubility by a seven-amino-acid insertion in the N-terminal arm and one positively selected amino acid site in the C-terminal extension.


CONCLUSIONS
Functional conservation of the ACD of Rhododendron CT1sHSP genes was inferred b
Liao
Pei-Chun
PC
Department of Life Science, Pingtung University of Science and Technology, Pingtung 91201, Taiwan.
Lin
Tsan-Piao
TP
Lan
Wei-Chieh
WC
Chung
Jeng-Der
JD
Hwang
Shih-Ying
SY
D000595:Amino Acid Sequence; D019143:Evolution, Molecular; D020440:Gene Duplication; D014644:Genetic Variation; D050888:Heat-Shock Proteins, Small / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D017434:Protein Structure, Tertiary; D029793:Rhododendron / Q000235:genetics*; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D013045:Species Specificity
D050888:Heat-Shock Proteins, Small; D010940:Plant Proteins