Studies on Expansin Super Family from Rice

Studies on Expansin Super Family from Rice


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- Date/Time : Wed June 18., 2003


                16:00-17:00 

- Speaker : Dr. Lee, Yi


             - 미시간 주립대 Plant Research Laboratory   

- Place : Life Science Bldg. #104

- For inquires : Professor Ildoo Hwang Dept. of Life Science


            생명과학과 황일두 교수 (☎279-2291)

Abstract -


 Expansins were first identified as cell-wall-loosening proteins that, at least in part, mediate pH-dependent extension of the plant cell wall and growth of the cell. More recently, it has been realized that expansins belong to four protein families, the α- and  -expansins, expansin-like (EXPL), and expansin-related (EXPR) genes and that they appear to be involved in regulating, besides cell expansion, a variety of plant processes, including morphogenesis, softening of fruits, and growth of the pollen tube of grasses through the stigma and the style.  The Arabidopsis genome contains 26 α-expansin genes and the rice genome at least 33. There are more  -expansin genes in monocots than in dicots, at least 18 in rice and five in Arabidopsis. Rice and Arabidopsis contain 4 and 3 EXPL genes, respectively, and 1 EXPR gene each. The DNA and deduced amino acid sequences are highly conserved in each expansin subfamily. They have a series of conserved Cys residues in the N-terminal half of the protein, an HFD (histidine-phenylalanine-aspartate) motif in the central region, and a series of Trp residues near the carboxyl terminus. EXPL and EXPR proteins lack the HFD motif and have different numbers of Cys residues. The positions and numbers of conserved Trp residues at the C-terminal region are different from those of α- and  -expansins. An analysis of exon/intron structure led to the hypothesis that the four subfamilies of expansins evolved from a common ancestral gene.  Expansin genes are differentially expressed in deepwater rice, with especially high transcript levels in the growing region. Expression of expansin genes in the internode was induced by treatment with gibberellin and by wounding. The wound response resulted from excising stem sections or from piercing pinholes into the stem of intact plants. Expression of the Os-EXPL3 gene is correlated with elongation and slightly induced by applied GA. However, the expression of the Os-EXPL1 and Os-EXPL2 genes showed limited correlation with cell elongation and was not induced by GA. We found no expression of the Os-EXPR1 gene in the organs examined.  Expansins are localized in plant cell walls, especially in primary cell walls. α-Expansins bind tightly to cell walls and could be separated from the cell wall only by SDS treatment. Modification of expansin gene expression altered the height of rice and size of cultured tobacco cells.