Mutation in the putative ketoacyl-ACP reductase CaKR1 induces loss of pungency in Capsicum
Mutation in the putative ketoacyl-ACP reductase CaKR1 induces loss of pungency in Capsicum
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DOI：
10.1007/s00122-018-3195-2
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发表时间：
2019-01-01
影响因子：
5.4
通讯作者：
Tanaka, Yoshiyuki
中科院分区：
文献类型：
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作者：
Koeda, Sota;Sato, Kosuke;Tanaka, Yoshiyuki
关键信息通过基于图谱的克隆和功能表征，鉴定出一种假定的酮酰基-ACP 还原酶 (CaKR1)，该酶以前并不知道与辣椒的刺激性有关。 摘要 辣椒果实的刺激性是由于存在辣椒素，而辣椒素是通过苯丙素和支链脂肪酸途径的聚合合成的。全球范围内辛辣和非辛辣辣椒的广泛使用凸显了了解类辣椒素生物合成的遗传机制对于育种辣椒品种的重要性。尽管辣椒是最早驯化的植物属之一，但其失去辣味的唯一报道的遗传原因是酰基转移酶 (Pun1) 和推定的转氨酶 (pAMT) 的突变。在这项研究中，利用来自 Habanero 和 No.3341 杂交的 F-2 群体，在 10 号染色体上鉴定了导致辣椒 No.3341 (C. chinense) 不辣的单个隐性基因。在目标区域中鉴定出5个候选基因，距离220kb。 No.3341 的候选基因，即假定的酮酰基-ACP 还原酶 (CaKR1)，在第一个内含子中插入了 4.5 kb 转座元件 (TE) 序列，导致产生缺失编码催化结构域的截短转录本。病毒诱导的辛辣辣椒中 CaKR1 基因沉默导致辣椒素积累减少，这一表型与 No.3341 一致。此外，预计在支链脂肪酸生物合成的延伸循环过程中合成的8-甲基-6-壬烯酸的GC-MS分析揭示了No.3341中的缺陷。遗传、基因组、转录、沉默和生化前体分析相结合，为 CaKR1 参与类辣椒素生物合成及其破坏导致辣味丧失的结论提供了坚实的基础。
Key messageA putative ketoacyl-ACP reductase (CaKR1) that was not previously known to be associated with pungency of Capsicum was identified from map-based cloning and functional characterization.AbstractThe pungency of chili pepper fruits is due to the presence of capsaicinoids, which are synthesized through the convergence of the phenylpropanoid and branched-chain fatty acid pathways. The extensive, global use of pungent and non-pungent peppers underlines the importance of understanding the genetic mechanism underlying capsaicinoid biosynthesis for breeding pepper cultivars. Although Capsicum is one of the earliest domesticated plant genera, the only reported genetic causes of its loss of pungency are mutations in acyltransferase (Pun1) and putative aminotransferase (pAMT). In this study, a single recessive gene responsible for the non-pungency of pepper No.3341 (C. chinense) was identified on chromosome 10 using an F-2 population derived from a cross between Habanero and No.3341. Five candidate genes were identified in the target region, within a distance of 220kb. A candidate gene, a putative ketoacyl-ACP reductase (CaKR1), of No.3341 had an insertion of a 4.5-kb transposable element (TE) sequence in the first intron, resulting in the production of a truncated transcript missing the region coding the catalytic domain. Virus-induced gene silencing of CaKR1 in pungent peppers resulted in the decreased accumulation of capsaicinoids, a phenotype consistent with No.3341. Moreover, GC-MS analysis of 8-methyl-6-nonenoic acid, which is predicted to be synthesized during the elongation cycle of branched-chain fatty acid biosynthesis, revealed that its deficiency in No.3341. Genetic, genomic, transcriptional, silencing, and biochemical precursor analyses performed in combination provide a solid ground for the conclusion that CaKR1 is involved in capsaicinoid biosynthesis and that its disruption results in a loss of pungency.