Two Novel Alkylresorcinol Synthase Genes from Sorghum; Cloning, Expression, Transformation and Characterization
申请人:Baerson Scott R.
公开号:US20110225676A1
公开(公告)日:2011-09-15
Sorghum is considered to be an allelopathic crop species, producing phytotoxins such as the lipid benzoquinone sorgoleone (2-hydroxy-5-methoxy-3-[(Z,Z)-8′,11′,14′-pentadecatriene]-p-benzoquinone) which likely accounts for much of its allelopathic properties. Prior investigations into the biosynthesis of sorgoleone have suggested the participation of one or more alkylresorcinol synthases (ARS), which are type III polyketide synthases (PKS) that produce 5-alkylresorcinols using medium to long-chain fatty acyl-CoA starter units via iterative condensations with malonyl-CoA. Current evidence suggests that sorgoleone biosynthesis occurs exclusively in root hair cells, involving the synthesis of a 5-pentadecatrienyl resorcinol intermediate derived from an unusual 16:3 fatty acyl-CoA starter unit. To characterize the enzymes responsible for the biosynthesis of this alkylresorcinol intermediate, a previously-described expressed sequence tag (EST) database prepared from isolated root hairs was first mined for all PKS-like sequences. Quantitative real-time RT-PCR analyses revealed that two of these sequences were preferentially expressed in root hairs, and recombinant enzyme studies demonstrated that both sequences (designated ARS1 and ARS2) encode ARS enzymes capable of accepting a variety of fatty acyl-CoA starter units. Furthermore, RNA interference (RNAi) experiments directed against ARS1 and ARS2 resulted in the generation of multiple independent transformant events exhibiting dramatically reduced sorgoleone levels. Thus, both ARS1 and ARS2 are likely to participate in the biosynthesis of sorgoleone in planta. The sequences of ARS1 and ARS2 were also used to identify several rice genes encoding ARSs, which are likely involved in the production of defense-related alkylresorcinols.
高粱被认为是一种化感作物,产生植物毒素,如脂肪苯醌sorgoleone(2-羟基-5-甲氧基-3-[(Z,Z)-8',11',14'-十五碳烯三烯基]-p-苯醌),这很可能解释了其大部分化感特性。对sorgoleone生物合成的先前研究表明,参与其中的是一种或多种烷基间苯酚合酶(ARS),它们是III型聚酮合酶(PKS),使用中到长链脂肪酰辅酶A起始单元通过与丙酰辅酶A的迭代缩合产生5-烷基间苯酚。目前的证据表明,sorgoleone生物合成仅发生在根毛细胞中,涉及从不寻常的16:3脂肪酰辅酶A起始单元衍生的5-十五碳烯三烯基间苯酚中间体的合成。为了表征负责合成这种烷基间苯酚中间体的酶,首先从分离的根毛制备的已描述表达序列标签(EST)数据库中挖掘所有类似于PKS的序列。定量实时RT-PCR分析表明,其中两个序列在根毛中优先表达,重组酶研究表明这两个序列(称为ARS1和ARS2)编码的ARS酶能够接受各种脂肪酰辅酶A起始单元。此外,针对ARS1和ARS2的RNA干扰(RNAi)实验导致产生多个独立的转化事件,其sorgoleone水平显著降低。因此,ARS1和ARS2都可能参与植物中sorgoleone的生物合成。ARS1和ARS2的序列还用于鉴定编码ARS的几个水稻基因,这些基因可能参与产生与防御相关的烷基间苯酚。