The proanthocyanidin-specific transcription factor MdMYBPA1 initiates anthocyanin synthesis under low temperature conditions in red-fleshed apple

First author: Nan Wang; Affiliations: Shandong Agricultural University (山东农业大学): Tai'an, China

Corresponding author: Xuesen Chen

In plants, flavonoids (黄酮类化合物) play critical roles in resistance to biotic and abiotic stresses, and contribute substantially to the quality, flavor, and nutritional quality of many fruit crops. In apple (Malus × domestica), inbreeding has resulted in severe decreases in the genetic diversity and flavonoid content. During the last decade, we focused on the genetic improvement of apple using wild red‐fleshed apple resources (Malus sieversii f. niedzwetzkyana). Here, we found that the MYB transcription factors (TFs) involved in the synthesis of proanthocyanidins (原花青素) can be classified into TT2 and PA1‐ ypes. We characterized a PA1‐ ype MYB transcription factor, MdMYBPA1, from red‐fleshed apple and identified its role in flavonoid biosynthesis using overexpression and knockdown‐expression transgenes in apple calli (愈伤组织). We explored the relationship between TT2‐ and PA1‐ ype MYB TFs, and found that MdMYB9/11/12 bind the MdMYBPA1 promoter. In addition, MdMYBPA1 responded to low temperature by redirecting the flavonoid biosynthetic pathway from proanthocyanidin to anthocyanin production. In binding analyses, MdbHLH33 directly bound to the LTR cis‐element of the MdMYBPA1 promoter and promotes its activity. Besides, the calli expressing both MdMYBPA1 and MdbHLH33, which together form a complex, produced more anthocyanin under low temperature. Our findings shed light on the essential roles of PA1‐ ype TFs in the metabolic network of proanthocyanidin and anthocyanin synthesis in plants. In addition, studies on red‐fleshed wild apple are beneficial for breeding new apple varieties with high flavonoid contents.

在植物中，黄酮类化合物在生物和非生物胁迫中扮演重要作用，同时在水果作物的果实品质、风味及营养价值方面发挥重要作用。在苹果中，自交导致了遗传多样性和黄酮类化合物含量的严重降低。近十年，作者着重关注了红色果肉的野生苹果品种的遗传改良。本文，作者发现MYB转录因子参与了原花青素的生物合成，这些MYB转录因子可以分为两大类，分别是TT2和PA1。作者对红色果肉苹果的PA1类的MYB转录因子MdMYBPA1基因进行了功能鉴定，同时通过在苹果愈伤组织过表达和敲低表达等转基因技术鉴定了其在类黄酮生物合成中的作用。作者研究了TT2和PA1类MYB转录因子之间的关系，发现MdMYB9/11/12基因结合在MdMYBPA1启动子区。另外，MdMYBPA1基因响应低温条件，将类黄酮生物合成通路从产原花青素转向为产花青素。在结合试验中，MdbHLH33基因会直接结合到MdMYBPA1基因启动子区的LTR顺式作用元件，并促进其活性。此外，同时表达MdMYBPA1和MdbHLH33基因的愈伤组织在低温条件下产生了更多的花青素。本文的研究揭示了PA1类转录因子在植物原花青素和花青素合成的代谢网络中的作用。另外，对于红色果肉的野生苹果品种的研究对于增加类黄酮含量的苹果新品种育种具有参考意义。

通讯：陈学森 (http://yyxy.sdau.edu.cn/2012/0528/c1457a15088/page.htm)

研究方向：水果种质资源挖掘、创制与利用。

doi: https://doi.org/10.1111/tpj.14013

Journal: the plant journal

First Published: 06 July, 2018

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