其他摘要 | NAC domain proteins are plant-specific transcriptional factors known to play diverse roles in various plant developmental processes. 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 Populus.In the present study, a comprehensive analysis of NAC gene family in Populus was performed. A total of 163 full-length NAC genes were identified in Populus, 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 Populus 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.Based on the genomic organizations, we can conclude that segmental duplications contribute significantly to the expansion of Populus 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 Populus 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.Cellulose is required for the cell wall integrity of root hair growing tips, but little is known about the genes involved in cellulose synthesis during root-hair morphogenesis. AtCSLD3 has been shown to be essential for root hair formation and cellulose biosynthesis during root hair morphogenesis. Here we characterized two poplar cellulose synthase-like (CSL) genes, PdCSLD5 and PdCSLD6, the closest orthologs to AtCSLD3. A phylogenetic tree was constructed from alignments of 30 poplar, 34 Rice and 29 Arabidopsis CSL protein sequences, and PdCSLD5 and PdCSLD6 were placed in a monophyletic clade with AtCSLD3. PdCSLD5 and PdCSLD6 both exhibit 86% similarity to AtCSLD3. The gene structure analysis revealed that PdCSLD5 and PdCSLD6, along with AtCSLD3, have similar intron/exon organizations, including three exons and two intronsExpression analysis showed PdCSLD5 and PdCSLD6 expressed in every organ with highest transcript level in roots. Subcellular localization analysis showed PdCSLD5 and PdCSLD6 were located in the apical plasma membranes of growing root hairs and in Golgi of the non-root hair forming cells. Furthermore, the localization pattern can be rewhen treated with reactive oxygen species (ROS) Expression of PdCSLD5 or PdCSLD6 in atcsld3 was able to partially or completely rescue the root-hair defects caused by the disruption of AtCSLD3, respectively. Cell wall sugar composition analysis showed increased glucose content and the decreased crystalline cellulose content of the cell wall preparation in the atcsld3 mutant. Immunolocalization analysis using the monoclonal antibodies CCRC-M1,CCRC-M87,CCRC-M38 and LM10 that recognize xyloglucan, homogalacturonan and xylan, respectively, recealed no significant difference of the fluorescent signals between the different Arabidopsis lines, indicating that PdCSLD6 and AtCSLD3 may not be involved in biosynthesis of polysaccharides mentioned above. Analysis with CBM3a and CBM17 that recognize crystalline cellulose and noncrystalline β-1,4-glucan, respectively showed increased noncrystalline β-1,4-glucan and decreased crystalline cellulose content in atcsld3, as well as the increased noncrystalline β-1,4-glucan in the PdCSLD6-overexpressed lines. All these changes in the cell wall sugar composition could be restored to the wild type level by expression of PdCSLD6 in atcsld3 mutant. Taken together, our results demonstrate that PdCSLD5 and PdCSLD6 are functional orthologs of AtCSLD3, and may participate in the crystalline cellulose synthesis during root-hair formation. |
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