含有转录抑制结构域的转录因子MYB221和MYB156在杨树木质部发育过程中的功能鉴定

A number of wood-associated transcription factors might be involved in the coordinated regulation of wood formation. Among them, the best-characterized ones are a set of transcription factors belonging to the NAC and MYB families, and most of them act as activator in the biosynthesis of secondary cell wall so far. However, it is increasingly being recognized that repression of transcription plays a vital role in gene regulatory networks. Using Affymetrix microarray together with laser microdissection, we profiled gene expression in cambium, early xylem and mature xylem. Two R2R3-MYB transcription factors, MYB221 and MYB156, were found to be highly upregulated during xylem development, which belong to R2R3 subgroup 4 proteins, sharing both a conserved transcription silencing motif (pdLNLD/ELxiG/S) and a region potentially forming a zinc finger domain at their C-termini. The orthologous genes AtMYB4 in Arabidopsis thaliana, AmMYB308 in Antirrhinum majus repress the transcriptional express of C4H, 4CL, CAD genes. To determine the biological role of MYB221 and MYB156 in wood formation, we will characterized the genes by using genetic method, including gene knockout, gene over-expression, transfection assay, and so on. Our study will provides more detail information for further dissection of transcriptional network regulating the biosynthesis of secondary walls during wood formation.

木材形成的转录调控由众多转录因子共同参与。其中功能解析较为清楚的转录因子主要属于NAC和R2R3-MYB两大类基因家族。目前鉴定的NAC和R2R3-MYB类转录因子大多数参与木材形成的正向调控。但更多的研究表明转录抑制在基因表达调控网络中具有至关重要的作用。我们在前期借助激光显微切割和基因芯片技术，对杨树形成层、早期木质部和成熟木质部的基因表达进行差异比较，发现了两个含有转录抑制结构域(pdLNLD/ELxiG/S)的MYB类基因MYB221和MYB156,在木质部高水平特异表达。这两个基因在分类上属于MYB subgroup 4蛋白。其在模式植物同源基因AtMYB4、AmMYB308对C4H、4CL、CAD具有转录抑制作用。本研究将通过基因敲除、基因过量表达等分子生物学方法，鉴定杨树MYB221和MYB156在木质部发育过程中的作用，解析木材形成的转录抑制调控机制。

木材形成的转录调控由众多转录因子共同参与。其中功能解析较为清楚的转录因子主要属于NAC和R2R3-MYB两大类基因家族。目前鉴定的NAC和R2R3-MYB类转录因子大多数参与木材形成的正向调控。但更多的研究表明转录抑制在基因表达调控网络中具有至关重要的作用。本研究通过基因敲除、基因过量表达及其它相关的遗传学和分子生物学方法，鉴定具有转录抑制活性的杨树subgroup 4 MYB转录因子MYB221和MYB 156基因功能，以及其在木材形成转录调控网络中的作用。基因表达模式分析表明，目标基因在叶片和次生木质部等组织高水平表达，相应蛋白定位在细胞核中。PtoMYB221和PtoMYB156在植物细胞中表现出转录抑制活性。通过基因敲除、基因过量表达表明杨树MYB221和MYB156负调控木质素的生物合成。PtoMYB221负调控木质素合成的关键酶基因C4H、CCoAOMT和COMT。我们的研究结果表明有望通过调节一个或少数几个转录因子的表达，有效地调控木质素的合成，达到改良木质纤维品质的目的。