Characterization and Expression Analysis of a Putative a-L-Arabinofuranosidase/p-D-xylosidase Gene Derived from Avocado

摘要

Cell wall is an important component which decides growth, volume, shape of plant cells. Alternation of its structure also affects various aspects of plant development. In this study, we obtained a cDNA clone encoding an a-L-arabinofuranosidase/ (3-D-xylosidase from avocado fruit. The clone, designated as PaArf/Xyl3A, contained 3,002 nucleotides which encoded 777 amino acid residues with a calculated molecular mass of 83.4 kDa. The deduced amino acid sequence contained a putative signal peptide. Calculated molecular mass of the truncated protein was 80 kDa consisting of 745 amino acid residues. In addition, there were two potential N-linked glycosylation sites, suggesting that PaArf/Xyl3A would be exported to the apoplast where the enzyme could hydrolyze on cell wall polysaccharides. Phylogenetic analysis showed that PaArf/Xyl3A clustered near other plant a-L-arabinofuranosidases/p-D-xylosidases exhibiting a preferential arabinosyl hydrolyzing activity against natural polysaccharides. These resultsindicated that the protein would be secreted from cytosol to cell wall (apoplast) and might act as an a-L-arabinofuranosidase against natural polysaccharides. Accumulation of the mRNA was detected in the fruit right after harvest and other active growingorgans such as immature leaves, expanded young leaves, germinating seedling and roots. According to the expression pattern and the phylogenetic relationship, PaArf/Xyl3A might be involved in arabinose metabolism and change to cell-to-cell contact of avocado during cell division/proliferation stage.