Liao Liao, Vimolmangkang Sornkanok, Wei Guochao, Zhou Hui, Korban Schuyler S, Han Yuepeng
Key Laboratory of Plant Germplasm Enhancement and Specialty Agriculture, Wuhan Botanical Garden of the Chinese Academy of Sciences Wuhan, China.
Key Laboratory of Plant Germplasm Enhancement and Specialty Agriculture, Wuhan Botanical Garden of the Chinese Academy of Sciences Wuhan, China ; Department of Pharmacognosy and Pharmaceutical Botany, Faculty of Pharmaceutical Sciences, Chulalongkorn University Bangkok, Thailand.
Front Plant Sci. 2015 Apr 10;6:243. doi: 10.3389/fpls.2015.00243. eCollection 2015.
Proanthocyanidins (PAs) are the major component of phenolics in apple, but mechanisms involved in PA biosynthesis remain unclear. Here, the relationship between the PA biosynthesis and the expression of genes encoding leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR) was investigated in fruit skin of one apple cultivar and three crabapples. Transcript levels of LAR1 and ANR2 genes were significantly correlated with the contents of catechin and epicatechin, respectively, which suggests their active roles in PA synthesis. Surprisingly, transcript levels for both LAR1 and LAR2 genes were almost undetectable in two crabapples that accumulated both flavan-3-ols and PAs. This contradicts the previous finding that LAR1 gene is a strong candidate regulating the accumulation of metabolites such as epicatechin and PAs in apple. Ectopic expression of apple MdLAR1 gene in tobacco suppresses expression of the late genes in anthocyanin biosynthetic pathway, resulting in loss of anthocyanin in flowers. Interestingly, a decrease in PA biosynthesis was also observed in flowers of transgenic tobacco plants overexpressing the MdLAR1 gene, which could be attributed to decreased expression of both the NtANR1 and NtANR2 genes. Our study not only confirms the in vivo function of apple LAR1 gene, but it is also helpful for understanding the mechanism of PA biosynthesis.
原花青素（PAs）是苹果中酚类物质的主要成分，但PA生物合成所涉及的机制仍不清楚。在此，研究了一个苹果品种和三个海棠果实表皮中PA生物合成与编码无色花青素还原酶（LAR）和花青素还原酶（ANR）的基因表达之间的关系。LAR1和ANR2基因的转录水平分别与儿茶素和表儿茶素的含量显著相关，这表明它们在PA合成中发挥着积极作用。令人惊讶的是，在积累了黄烷-3-醇和PA的两个海棠中，几乎检测不到LAR1和LAR2基因的转录水平。这与之前的发现相矛盾，即LAR1基因是调控苹果中表儿茶素和PA等代谢物积累的有力候选基因。苹果MdLAR1基因在烟草中的异位表达抑制了花青素生物合成途径中晚期基因的表达，导致花朵中花青素缺失。有趣的是，在过表达MdLAR1基因的转基因烟草植株的花朵中也观察到PA生物合成减少，这可能归因于NtANR1和NtANR2基因表达的降低。我们的研究不仅证实了苹果LAR1基因在体内的功能，也有助于理解PA生物合成的机制。
