Plant Molecular Biology Division, Rajiv Gandhi Centre for Biotechnology, Thycaud (P.O), Thiruvananthapuram, 695 014, Kerala, India.
Gene. 2012 Jan 10;491(2):278-83. doi: 10.1016/j.gene.2011.09.025. Epub 2011 Oct 1.
Type III polyketide synthase family of enzymes play an important role in the biosynthesis of flavonoids and a variety of plant polyphenols by condensing multiple acetyl units derived from malonyl Co-A to thioester linked starter molecules covalently bound in the PKS active site. Turmeric (Curucma longa L.) through diverse metabolic pathways produces a large number of metabolites, of which curcuminoids had gained much attention due to its immense pharmaceutical value. Recent identification of multiple curcuminoid synthases from turmeric lead us to look for additional Type III PKS from this plant. The current study describes the occurrence of a multigene family of Type III PKS enzymes in C. longa by RT-PCR based genomic screening. We have also isolated two new Type III PKS, ClPKS9 and ClPKS10 using homology based RT-PCR and data mining. The comparative sequence and phylogenetic analysis revealed that the two PKSs belong to different groups with only 56% sequence similarity at their amino acid level. ClPKS9 shows all possible sequence requirements for a typical chalcone synthase whereas ClPKS10 shows promising variation at amino acid level and high similarity to reported curcuminoid synthases. ClPKS9 and ClPKS10 exhibited distinct tissue specific expression pattern in C. longa with the ClPKS9 transcript abundant in shoot and rhizome than leaves whereas ClPKS10 transcript was found to be high in leaf and very low in rhizome and root. Therefore it was concluded that ClPKS9 and ClPKS10 may have divergent function in planta, with possible role in typical chalcone forming reaction and curcuminoid scaffold biosynthetic pathway respectively.
III 型聚酮合酶家族的酶通过将来自丙二酰辅酶 A 的多个乙酰基单元缩合到共价结合在 PKS 活性位点中的硫酯连接起始分子上来在类黄酮和各种植物多酚的生物合成中发挥重要作用。姜黄（Curucma longa L.）通过多种代谢途径产生大量代谢物，其中由于其巨大的药用价值，姜黄素备受关注。最近从姜黄中鉴定出多种姜黄素合酶，这促使我们从这种植物中寻找其他 III 型 PKS。本研究通过基于 RT-PCR 的基因组筛选描述了 C. longa 中 III 型 PKS 酶的多基因家族的发生。我们还使用基于同源性的 RT-PCR 和数据挖掘从该植物中分离出两种新的 III 型 PKS，ClPKS9 和 ClPKS10。比较序列和系统发育分析表明，这两种 PKS 属于不同的组，其氨基酸水平的序列相似性仅为 56%。ClPKS9 显示出典型查尔酮合酶的所有可能的序列要求，而 ClPKS10 在氨基酸水平上表现出有希望的变化，并且与报道的姜黄素合酶高度相似。ClPKS9 和 ClPKS10 在 C. longa 中表现出明显的组织特异性表达模式，ClPKS9 转录本在茎和根茎中比在叶片中丰富，而 ClPKS10 转录本在叶片中丰富，在根茎和根中非常低。因此，得出结论，ClPKS9 和 ClPKS10 在植物体内可能具有不同的功能，可能分别在典型的查尔酮形成反应和姜黄素支架生物合成途径中发挥作用。
