p-Coumaroyl-CoA:monolignol transferase (PMT) acts specifically in the lignin biosynthetic pathway in Brachypodium distachyon.
p-Coumaroyl-CoA:monolignol transferase (PMT) acts specifically in the lignin biosynthetic pathway in Brachypodium distachyon.
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DOI：
10.1111/tpj.12420
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发表时间：
2014-03
期刊：
影响因子：
--
通讯作者：
Sedbrook JC
中科院分区：
文献类型：
--
作者：
Petrik DL;Karlen SD;Cass CL;Padmakshan D;Lu F;Liu S;Le Bris P;Antelme S;Santoro N;Wilkerson CG;Sibout R;Lapierre C;Ralph J;Sedbrook JC
草类木质素含有大量的p-香豆酸(PCA)，可使苯丙烷类聚合物主链的侧链酰化。最近从水稻中鉴定出一种酰基转移酶，命名为p-香豆酰-辅酶A：单甘醇转移酶(OsPMT)，它能在体外与PCA发生酰化反应。在植物中，这样的单烯醇基-PCA偶联物通过氧化自由基偶联作用被结合到木质素中，从而产生观察到的PCA附件；然而，p-香豆酸酯也使草中的阿拉伯木聚糖酰化。为了验证PMT作为一种木质素生物合成途径酶的真实性，我们研究了BdPMT基因功能改变的短柄青霉植株。利用新开发的细胞壁分析方法，我们确定该转移酶特异性地参与了单酚酰化反应。叠氮化钠产生的Bdpmt-1错义突变体在木质素上没有(<；0.5%)残留的PCA，BdPMT RNAi植株的水平低至野生型的10%，而这些PMT突变植株的阿拉伯木聚糖上的PCA酰化阿拉伯糖基单位的数量没有变化。BdPMT高表达植物的木质素的PCA酰化水平比野生型高三倍以上，但阿拉伯糖基单位的水平没有变化。综上所述，这些数据与GRASS PMT基因在编码BAHD(BEAT、AHCT、HCBT和DAT)酰基转移酶中的明确作用是一致的，BAHD酰基转移酶专门与PCA酰化单醇，并产生用于植物木质化的单烯醇基对香豆酸结合物。
Grass lignins contain substantial amounts of p-coumarate (pCA) that acylate the side-chains of the phenylpropanoid polymer backbone. An acyltransferase, named p-coumaroyl-CoA:monolignol transferase (OsPMT), that could acylate monolignols with pCA in vitro was recently identified from rice. In planta, such monolignol-pCA conjugates become incorporated into lignin via oxidative radical coupling, thereby generating the observed pCA appendages; however p-coumarates also acylate arabinoxylans in grasses. To test the authenticity of PMT as a lignin biosynthetic pathway enzyme, we examined Brachypodium distachyon plants with altered BdPMT gene function. Using newly developed cell wall analytical methods, we determined that the transferase was involved specifically in monolignol acylation. A sodium azide-generated Bdpmt-1 missense mutant had no (<0.5%) residual pCA on lignin, and BdPMT RNAi plants had levels as low as 10% of wild-type, whereas the amounts of pCA acylating arabinosyl units on arabinoxylans in these PMT mutant plants remained unchanged. pCA acylation of lignin from BdPMT-overexpressing plants was found to be more than three-fold higher than that of wild-type, but again the level on arabinosyl units remained unchanged. Taken together, these data are consistent with a defined role for grass PMT genes in encoding BAHD (BEAT, AHCT, HCBT, and DAT) acyltransferases that specifically acylate monolignols with pCA and produce monolignol p-coumarate conjugates that are used for lignification in planta.
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