Characterization Of Wheat Jrl Gene And Dir Gene Families

Plants are sessile and must adapt to various environmental conditions and stresses, such as high salinity, water and nutrient deficiencies, low and high temperatures, infection by diseases, and attacks by insect pests. At the genome level, this type of adaptive evolution is exemplified by the rapid amplification and functional diversification of the gene families involved in stress responses. Both jacalin-related lectins (JRLs) and dirigent (DIR) family genes have been reported particitation in plant respond to biotic and abiotic challenges. An investigation of these genes would shed light on the evolutionary and functional mechanisms by which plants respond to variable growth environments and lead to the identification of genes critical for crop improvement.JRLs are carbohydrate-binding proteins and involve in various biological processes. In the presence of homeologous subgenomes, the67genes may encompass orthologs from unidentified homoeologous loci. Grouping using95%identity yielded56unique genes, with approximately18genes per sub-genome. We therefore concluded that at the subgenome level, wheat is similar to Brachypodium, sorghum, and maize in JRL gene number but has fewer genes than Arabdopsis (47) and rice (31). JRL proteins are variability in sequence length and domain arhitectures. Compared with the structure of JRL Heltuba and Banlec, thirty-three highly conserved residues showing at least85%similarity. Of the12key residues necessary for the integrity of the β-prism fold of Heltuba,11were conserved in wheat JRLs and one was conserved when75%chemical similarity was used as the cutoff, implying most TaJRL jacalin domains adopt the β-prism structure. Nine new conserved residues were identified in the wheat jacalin domains, including three in133, two in β4, one in β5, one within β5-β6loop, one in β8, and one in β12. Nearly half of the wheat jacalin domains had two carbohydrate-bingidng sites.Domain architectures of JRL proteins are diverse. Our data showed percentage of holo-JRL in Arabidopsis higher than grass plants and percentage of chimeric JRL lower than grass plants. The domain content and organizations are very similar among grass members but different with Arabidopsis in this family. This finding suggests that the domain organization of JRL family was established after the Arabidopsis-grass split and before grass speciation. DJRL, which contains an N-terminal dirigent domain and a C-terminal jacalin domain, are very likely specific to grass plants. The correlation analysis revealed that the divergent evolution of the N termini from one another is highly positive correlated with the divergent evolution of the C termini from one another.To infer the evolutionary relationships of JRL proteins in different plant species, a phylogenetic tree was constructed using the conserved jacalin domains in the rice, Arabdopsis, sorghum, maize, and Brachypodium jacalin proteins. This tree revealed eight clades. Most of AURL members fell into its own subclass, separating from monocot plants. Members from five grass species intended to be clustered together, exhibiting lineage-specific expansion. The clade Ⅱ cereal JRLs, like A. thaliana JRLs, had a conserved WDDG motif, although this region is poorly conserved in cereal JRLs on the whole. It could therefore be speculated that this clade represents the more ancient JRLs.Digital expression data showed that most of the wheat JRL genes were predominately expressed in vegetative tissues (including root, leaf, stem, shoot and crown) but rare in seed. Fifty of the identified TaJRL genes had ESTs from treated tissues, and36showed significant induction by biotic and/or abiotic treatments, accounting for53.7%of the identified TaJRL genes. Indition, another13JRL genes were responsive to at least one of the abiotic treatments and9genes were induced by at least one of the biotic treatments via sqPCR.23JRL genes showed up regulation by at least one of three stress hormones. These data imply most wheat JRL genes play important roles in stresses adaptation to wheat.Dirigent proteins (DIRs) are critically involved in the formation of lignans, a diverse and widely distributed class of secondary plant metabolites exhibiting interesting pharmacological activities and implicated in natural plant defense. In this study, a total of135and44DIR genes were identified in wheat and poplar. While8and1new DIR genes were identified in rice and Arabdopsis genome, respectively. DIR proteins are variability in sequence. Most PtDIR and AtDIR genes have no intron and1/3OsDIR genes have1-5introns. Most DIR proteins contain single dirigent domain. A large number of DIR genes were expanded via gene duplication,29PtDIR,45OsDIR and10AtDIR genes were tandemly duplicated, respectively. There are19and4genes were segmentally duplicated in poplar and rice genomes, respectively. Digital expression data showed that wheat DIR genes were expressed in different tissues.30%TaDIR genes showed significant induction by biotic and/or abiotic treatments. This study will facilitate further studies on DIR family and provide useful clues for functional validation of DIR genes in higher plants.