The Endo-β-Mannanase gene families in Arabidopsis, rice, and poplar.

Mannans are widespread hemicellulosic polysaccharides in plant cell walls. Hydrolysis of the internal β-1,4- d-mannopyranosyl linkage in the backbone of mannans is catalyzed by endo-β-mannanase. Plant endo-β-mannanase has been well studied for its function in seed germination. Its involvement in other plant biological processes, however, remains poorly characterized or elusive. The completed genome sequences of Arabidopsis ( Arabidopsis thaliana), rice ( Oryza sativa), and poplar ( Populus trichocarpa) provide an opportunity to conduct comparative genomic analysis of endo- β-mannanase genes in these three species. In silico sequence analysis led to the identification of eight, nine and 11 endo-β-mannanase genes in the genomes of Arabidopsis, rice, and poplar, respectively. Sequence comparisons revealed the conserved amino acids and motifs that are critical for the active site of endo-β-mannanases. Intron/exon structure analysis in conjunction with phylogenetic analysis implied that both intron gain and intron loss has played roles in the evolution of endo-β-mannanase genes. The phylogenetic analysis that included the endo-β-mannanases from plants and other organisms implied that plant endo-β-mannanases have an ancient evolutionary origin. Comprehensive expression analysis of all Arabidopsis and rice endo- β-mannanase genes showed divergent expression patterns of individual genes, suggesting that the enzymes encoded by these genes, while carrying out the same biochemical reaction, are involved in diverse biological processes. [ABSTRACT FROM AUTHOR]