Graduate School of Agriculture, Kyoto University, Kyoto, Kyoto, 606-8502, Japan.
Chiba University, Chiba, 271-8510, Japan.
Planta. 2022 Jul 24;256(3):47. doi: 10.1007/s00425-022-03958-4.
A novel gene belonging to the aldo-keto reductase 13 family is involved in isoliquiritigenin biosynthesis in dahlia. The yellow pigments of dahlia flowers are derived from 6'-deoxychalcones, which are synthesized via a two-step process, involving the conversion of 3-malonyl-CoA and 4-coumaloyl-CoA into isoliquiritigenin in the first step, and the subsequent generation of butein from isoliquiritigenin. The first step reaction is catalyzed by chalcone synthase (CHS) and aldo-keto reductase (AKR). AKR has been implicated in the isoflavone biosynthesis in legumes, however, isolation of butein biosynthesis related AKR members are yet to be reported. A comparative RNA-seq analysis between two dahlia cultivars, 'Shukuhai' and its butein-deficient lateral mutant 'Rinka', was used in this study to identify a novel AKR gene involved in 6'-deoxychalcone biosynthesis. DvAKR1 encoded a AKR 13 sub-family protein with significant differential expression levels, and was phylogenetically distinct from the chalcone reductases, which belongs to the AKR 4A sub-family in legumes. DNA sequence variation and expression profiles of DvAKR1 gene were correlated with 6'-deoxychalcone accumulation in the tested dahlia cultivars. A single over-expression analysis of DvAKR1 was not sufficient to initiate the accumulation of isoliquiritigenin in tobacco, in contrast, its co-overexpression with a chalcone 4'-O-glucosyltransferase (Am4'CGT) from Antirrhinum majus and a MYB transcription factor, CaMYBA from Capsicum annuum successfully induced isoliquiritigenin accumulation. In addition, DvAKR1 homologous gene expression was detected in Coreopsideae species accumulating 6'-deoxychalcone, but not in Asteraceae species lacking 6'-deoxychalcone production. These results not only demonstrate the involvement of DvAKR1 in the biosynthesis of 6'-deoxychalcone in dahlia, but also show that 6'-deoxychalcone occurrence in Coreopsideae species developed evolutionarily independent from legume species.
一种属于醛酮还原酶 13 家族的新基因参与了大丽花中异甘草素的生物合成。大丽花的黄色色素来源于 6'-去氧查尔酮，它通过两步合成，第一步是将 3-丙二酰辅酶 A 和 4-肉桂酰辅酶 A 转化为异甘草素，然后由异甘草素生成白杨素。第一步反应由查尔酮合酶（CHS）和醛酮还原酶（AKR）催化。AKR 已被证明参与了豆科植物异黄酮的生物合成，然而，尚未报道与白杨素生物合成相关的 AKR 成员的分离。本研究采用比较 RNA-seq 分析两种大丽花品种“Shukuhai”及其白杨素缺陷侧突变体“Rinka”，鉴定了一个新的参与 6'-去氧查尔酮生物合成的 AKR 基因。DvAKR1 编码的 AKR 13 亚家族蛋白具有显著的差异表达水平，与属于豆科 AKR 4A 亚家族的查尔酮还原酶在系统发育上不同。DvAKR1 基因的 DNA 序列变异和表达谱与测试的大丽花品种中 6'-去氧查尔酮的积累相关。DvAKR1 的单一过表达分析不足以在烟草中引发异甘草素的积累，相反，它与金鱼草的查尔酮 4'-O-葡萄糖基转移酶（Am4'CGT）和辣椒的 MYB 转录因子 CaMYBA 的共过表达成功诱导了异甘草素的积累。此外，在积累 6'-去氧查尔酮的 Coreopsideae 物种中检测到 DvAKR1 同源基因的表达，但在缺乏 6'-去氧查尔酮产生的 Asteraceae 物种中没有检测到。这些结果不仅证明了 DvAKR1 参与了大丽花中 6'-去氧查尔酮的生物合成，还表明 Coreopsideae 物种中 6'-去氧查尔酮的出现是从豆科植物中独立进化而来的。
