每日摘要：微管蛋白在楊樹葉片細胞壁中的作用

Tubulins, rhythms and cell walls in poplar leaves: it』s all in the timing

First author:Scott A. Harding; Affiliations: University of Georgia (喬治亞大學): Athens, USA

Corresponding author:Chung-Jui Tsai

Plant cell walls exhibit architectural and compositional changes throughout their development and in response to external cues. While tubulins (微管蛋白) are involved in cell wall biogenesis, much remains unknown about the scope of their involvement (參與) during the orchestration of this resource-demanding process. A transgenic approach coupled with cell wall compositional analysis, RNA-seq and mining of publicly available diurnal gene expression data was used to assess the involvement of tubulins in poplar leaf cell wall biogenesis. Leaf cell walls of transgenic poplar lines with constitutive overexpression of α-tubulin (TUA) exhibited an increased abundance of homogalacturonan (同型半乳糖醛酸聚糖), along with a reduction in xylose (戊醛糖). These changes were traced to altered expression of UDP-glucuronic acid decarboxylase (GADC; UDP-葡萄糖醛酸脫羧酶) in the transgenic leaves. A model is postulated by which altered diurnal control of TUA through its constitutive overexpression led to a metabolic tradeoff affecting cellular utilization of GADC substrate UDP-glucuronic acid. While there were no effects on cellulose, hemicellulose or lignin abundance, subtle (微妙的) effects on hemicellulose composition and associated gene expression were noted. In addition, expression and enzymatic activity of pectin methylesterase (PME; 果膠甲酯酶) decreased in the transgenic leaves. The change is discussed in a context of increased levels of PME substrate homogalacturonan, slow stomatal kinetics (氣孔動力學) and the fate of PME product methanol (甲醇). Since stomatal opening and closing depend on fundamentally contrasting microtubule (微管) dynamics, the slowing of both processes in the transgenic lines as previously reported appears to be directly related to underlying cell wall compositional changes that were caused by tubulin manipulation.

植物細胞壁在整個發育時期和響應外界環境時會改變其結構與組成。微管蛋白參與了細胞壁的生物合成，然而對於其還參與了哪些生物學的過程還所知甚少。本文利用轉基因方法，結合細胞壁組成分析、RNA-seq及挖掘公共可利用的基因表達數據研究楊樹葉片細胞壁生物合成中微管蛋白的作用。組成型過表達α-微管蛋白（TUA）的轉基因楊樹葉片表現出同型半乳糖醛酸聚糖積累的增加，同時戊醛糖含量的降低。這些改變可以追溯到轉基因葉片中UDP-葡萄糖醛酸脫羧酶（GADC）基因表達的改變。通過過表達TUA改變其表達水平導致了植株代謝的平衡，進而影響了細胞內對GADC底物UDP-葡萄糖醛酸的利用。轉基因中過表達TUA對於纖維素、半纖維素及木質素含量均無影響，但對於半纖維素的組成有微小影響，同時也注意到相關基因的表達水平的變化。另外，轉基因植株中果膠甲酯酶表達及酶活有所降低。本文作者討論了轉基因植株中PME底物同型半乳糖醛酸聚糖含量升高、氣孔動力的減緩以及PME產物甲醇的速率等問題。由於氣孔開放與閉合基本取決於兩側微管動態的差異，轉基因株系中這些生物學進程的減緩顯然直接與由微管蛋白改變導致的潛在細胞壁組成的改變相關。

通訊：Chung-Jui Tsai(http://www.genetics.uga.edu/directory/chung-jui-tsai)

研究方向：利用轉錄組、代謝組、CRISPR基因組編輯、以及更多的傳統的遺傳學方法、生化及植物生理等手段來研究林木之所以為林木的原因，從基因家族進化和功能基因分化到生長發育重要基因的轉基因研究。

doi:https://doi.org/10.1093/treephys/tpx104

Journal:Tree Physiology

Published data: September 12, 2017.

（P.S. 歡迎訪問個人博客：https://plantfrontiers.wordpress.com）

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