Saensuk Chatree, Wanchana Samart, Choowongkomon Kiattawee, Wongpornchai Sugunya, Kraithong Tippaya, Imsabai Wachiraya, Chaichoompu Ekawat, Ruanjaichon Vinitchan, Toojinda Theerayut, Vanavichit Apichart, Arikit Siwaret
Rice Science Center, Kasetsart University Kamphaeng Saen Campus, Nakhon Pathom, 73140, Thailand; Interdisciplinary Graduate Program in Genetic Engineering, Kasetsart University, Bangkok, 10900, Thailand.
National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency (NSTDA), Khlong Luang, Pathum Thani, 12120, Thailand.
Plant Sci. 2016 Nov;252:324-334. doi: 10.1016/j.plantsci.2016.08.014. Epub 2016 Aug 28.
Thailand's aromatic coconut (Cocos nucifera L.) is a special type of green dwarf coconut, the liquid endosperm of which is characterized by a pleasant "pandan-like" aroma due to the presence of 2-acetyl-1-pyrroline (2AP). The aim of this study was to perform a de novo assembly of transriptome from C. nucifera endosperm and to identify the gene responsible for 2AP biosynthesis. CnAMADH2 was identified as an ortholog of the rice aromatic gene and a G-to-C substitution found in exon 14 was associated with 2AP content in the aromatic green dwarf coconut accessions. The base substitution caused an amino-acid change, alanine-to-proline, at position 442 (P442A). The presence of P at this position might alter the steric conformation at the loop region and subsequently result in an unstabilized dimer conformation that could lower AMADH enzyme activity. Among AMADH/BADH protein sequences in different plant species, the P442A mutation was found exclusively in aromatic coconut. The PCR marker developed based on this sequence variation can perfectly detect the aromatic and non-aromatic alleles of the gene. This study confirms the hypothesis that plants may share a mechanism of 2AP biosynthesis. This is the first identification of the gene associated with 2AP biosynthesis in a tree plant.
泰国香椰（Cocos nucifera L.）是一种特殊的绿矮椰品种，其液态胚乳因含有2-乙酰基-1-吡咯啉（2AP）而具有宜人的“类似香兰叶”的香气。本研究的目的是对椰果胚乳的转录组进行从头组装，并鉴定负责2AP生物合成的基因。CnAMADH2被鉴定为水稻香气基因的直系同源基因，在外显子14中发现的G到C的替换与香绿矮椰品种中的2AP含量相关。碱基替换导致第442位氨基酸由丙氨酸变为脯氨酸（P442A）。该位置脯氨酸的存在可能会改变环区的空间构象，进而导致二聚体构象不稳定，从而降低AMADH酶的活性。在不同植物物种的AMADH/BADH蛋白序列中，P442A突变仅在香椰中发现。基于该序列变异开发的PCR标记能够完美检测该基因的香和非香等位基因。本研究证实了植物可能共享2AP生物合成机制的假设。这是首次在木本植物中鉴定出与2AP生物合成相关的基因。
