Comprehensive Analysis of NAC Domain Transcription Factor Gene Family in Populus trichocarpa

<p>Abstract</p> <p>Background</p> <p>NAC (<b>NAM, ATAF1/2 </b>and <b>CUC2</b>) domain proteins are plant-specific transcriptional factors known to play diverse roles in various plant developmental processes. NAC transcription factors comprise of a large gene family represented by more than 100 members in <it>Arabidopsis</it>, rice and soybean etc. Recently, a preliminary phylogenetic analysis was reported for NAC gene family from 11 plant species. However, no comprehensive study incorporating phylogeny, chromosomal location, gene structure, conserved motifs, and expression profiling analysis has been presented thus far for the model tree species <it>Populus</it>.</p> <p>Results</p> <p>In the present study, a comprehensive analysis of NAC gene family in <it>Populus </it>was performed. A total of 163 full-length NAC genes were identified in <it>Populus</it>, and they were phylogeneticly clustered into 18 distinct subfamilies. The gene structure and motif compositions were considerably conserved among the subfamilies. The distributions of 120 <it>Populus </it>NAC genes were non-random across the 19 linkage groups (LGs), and 87 genes (73%) were preferentially retained duplicates that located in both duplicated regions. The majority of NACs showed specific temporal and spatial expression patterns based on EST frequency and microarray data analyses. However, the expression patterns of a majority of duplicate genes were partially redundant, suggesting the occurrence of subfunctionalization during subsequent evolutionary process. Furthermore, quantitative real-time RT-PCR (RT-qPCR) was performed to confirm the tissue-specific expression patterns of 25 NAC genes.</p> <p>Conclusion</p> <p>Based on the genomic organizations, we can conclude that segmental duplications contribute significantly to the expansion of <it>Populus </it>NAC gene family. The comprehensive expression profiles analysis provides first insights into the functional divergence among members in NAC gene family. In addition, the high divergence rate of expression patterns after segmental duplications indicates that NAC genes in <it>Populus </it>are likewise to have been retained by substantial subfunctionalization. Taken together, our results presented here would be helpful in laying the foundation for functional characterization of NAC gene family and further gaining an understanding of the structure-function relationship between these family members.</p

Genome-Wide Identification, Evolutionary Expansion, and Expression Profile of Homeodomain-Leucine Zipper Gene Family in Poplar (Populus trichocarpa)

BACKGROUND: Homeodomain-leucine zipper (HD-ZIP) proteins are plant-specific transcriptional factors known to play crucial roles in plant development. Although sequence phylogeny analysis of Populus HD-ZIPs was carried out in a previous study, no systematic analysis incorporating genome organization, gene structure, and expression compendium has been conducted in model tree species Populus thus far. PRINCIPAL FINDINGS: In this study, a comprehensive analysis of Populus HD-ZIP gene family was performed. Sixty-three full-length HD-ZIP genes were found in Populus genome. These Populus HD-ZIP genes were phylogenetically clustered into four distinct subfamilies (HD-ZIP I-IV) and predominately distributed across 17 linkage groups (LG). Fifty genes from 25 Populus paralogous pairs were located in the duplicated blocks of Populus genome and then preferentially retained during the sequential evolutionary courses. Genomic organization analyses indicated that purifying selection has played a pivotal role in the retention and maintenance of Populus HD-ZIP gene family. Microarray analysis has shown that 21 Populus paralogous pairs have been differentially expressed across different tissues and under various stresses, with five paralogous pairs showing nearly identical expression patterns, 13 paralogous pairs being partially redundant and three paralogous pairs diversifying significantly. Quantitative real-time RT-PCR (qRT-PCR) analysis performed on 16 selected Populus HD-ZIP genes in different tissues and under both drought and salinity stresses confirms their tissue-specific and stress-inducible expression patterns. CONCLUSIONS: Genomic organizations indicated that segmental duplications contributed significantly to the expansion of Populus HD-ZIP gene family. Exon/intron organization and conserved motif composition of Populus HD-ZIPs are highly conservative in the same subfamily, suggesting the members in the same subfamilies may also have conservative functionalities. Microarray and qRT-PCR analyses showed that 89% (56 out of 63) of Populus HD-ZIPs were duplicate genes that might have been retained by substantial subfunctionalization. Taken together, these observations may lay the foundation for future functional analysis of Populus HD-ZIP genes to unravel their biological roles

Functional conservation and divergence of Miscanthus lutarioriparius GT43 gene family in xylan biosynthesis

Background: Xylan is the most abundant un-cellulosic polysaccharides of plant cell walls. Much progress in xylan biosynthesis has been gained in the model plant species Arabidopsis. Two homologous pairs Irregular Xylem 9 (IRX9)/9L and IRX14/14L from glycosyltransferase (GT) family 43 have been proved to play crucial roles in xylan backbone biosynthesis. However, xylan biosynthesis in grass such as Miscanthus remains poorly understood

Genome-Wide Analysis of Sorghum GT47 Family Reveals Functional Divergences of MUR3-Like Genes

Sorghum (Sorghum bicolor) is an important bioenergy crop. Its biomass mainly consists of the cellulosic and non-cellulosic polysaccharides, both which can be converted to biofuels. The biosynthesis of non-cellulosic polysaccharides involves several glycosyltransferases (GT) families including GT47. However, there was no systemic study on GT47 family in sorghum to date. Here, we identified 39 sorghum GT47 family members and showed the functional divergences of MURUS3 (MUR3) homologs. Sorghum GT47 proteins were phylogenetically clustered into four distinct subfamilies. Within each subfamily, gene structure was relatively conserved between the members. Ten gene pairs were identified from the 39 GT47 genes, of which two pairs might be originated from tandem duplication. 25.6% (10/39) of sorghum GT47 genes were homologous to Arabidopsis MUR3, a xyloglucan biosynthesis gene in primary cell walls. SbGT47_2, SbGT47_7, and SbGT47_8, three most homologous genes of MUR3, exhibited different tissue expression patterns and were selected for complementation into Arabidopsis mur3-3. Physiological and cell wall analyses showed that SbGT47_2 and SbGT47_7 may be two functional xyloglucan galactosyltransferases in sorghum. Further studies found that MUR3-like genes are widely present in the seed plants but not in the chlorophytic alga Chlamydomonas reinhardtii. Our results provide novel information for evolutionary analysis and functional dissection of sorghum GT47 family members

Genome-wide mining seed-specific candidate genes from peanut for promoter cloning.

Peanut seeds are ideal bioreactors for the production of foreign recombinant proteins and/or nutrient metabolites. Seed-Specific Promoters (SSPs) are important molecular tools for bioreactor research. However, few SSPs have been characterized in peanut seeds. The mining of Seed-Specific Candidate Genes (SSCGs) is a prerequisite for promoter cloning. Here, we described an approach for the genome-wide mining of SSCGs via comparative gene expression between seed and nonseed tissues. Three hundred thirty-seven SSCGs were ultimately identified, and the top 108 SSCGs were characterized. Gene Ontology (GO) analysis revealed that some SSCGs were involved in seed development, allergens, seed storage and fatty acid metabolism. RY REPEAT and GCN4 motifs, which are commonly found in SSPs, were dispersed throughout most of the promoters of SSCGs. Expression pattern analysis revealed that all 108 SSCGs were expressed specifically or preferentially in the seed. These results indicated that the promoters of the 108 SSCGs may perform functions in a seed-specific and/or seed-preferential manner. Moreover, a novel SSP was cloned and characterized from a paralogous gene of SSCG29 from cultivated peanut. Together with the previously characterized SSP of the SSCG5 paralogous gene in cultivated peanut, these results implied that the method for SSCG identification in this study was feasible and accurate. The SSCGs identified in this work could be widely applied to SSP cloning by other researchers. Additionally, this study identified a low-cost, high-throughput approach for exploring tissue-specific genes in other crop species

The tubby-like proteins kingdom in animals and plants

Each gene of the tubby-like family is characterized by a signature of C-terminal tubby domain. The wide spread of this family in plants and animals implies they have an important function in various organisms. Even though the tubby-like genes are suggested to be putative transcription factors (TFs), how they execute the function as TFs is not yet clear. The biological functions of most animal tubby-like genes have been well studied, especially for vertebrate TUB, TULP1 and TULP3, but not with TULP2 and TULP4. Plants possess more tubby-like genes than animals, but their functions are still elusive except the idea that they are involved in stress responses with indistinct mechanisms. Here we reviewed the current knowledge of the versatile functions and roles of the tubby-like family members in plants and animals

Genome-Wide Identification and Expression Profiling Analysis of the Xyloglucan Endotransglucosylase/Hydrolase Gene Family in Tobacco (Nicotiana tabacum L.)

Xyloglucan endotransglucosylase/hydrolase genes (XTHs) encode enzymes required for the reconstruction and modification of xyloglucan backbones, which will result in changes of cell wall extensibility during growth. A total of 56 NtXTH genes were identified from common tobacco, and 50 cDNA fragments were verified by PCR amplification. The 56 NtXTH genes could be classified into two subfamilies: Group I/II and Group III according to their phylogenetic relationships. The gene structure, chromosomal localization, conserved protein domains prediction, sub-cellular localization of NtXTH proteins and evolutionary relationships among Nicotiana tabacum, Nicotiana sylvestrisis, Nicotiana tomentosiformis, Arabidopsis, and rice were also analyzed. The NtXTHs expression profiles analyzed by the TobEA database and qRT-PCR revealed that NtXTHs display different expression patterns in different tissues. Notably, the expression patterns of 12 NtXTHs responding to environment stresses, including salinity, alkali, heat, chilling, and plant hormones, including IAA and brassinolide, were characterized. All the results would be useful for the function study of NtXTHs during different growth cycles and stresses