A MYB/bHLH complex regulates tissue‐specific anthocyanin biosynthesis in the inner pericarp of red‐centered kiwifruit Actinidia chinensis cv. Hongyang

First author: Lihuan Wang; Affiliations: Sichuan University (四川大学): Chengdu, China

Corresponding author: Yongsheng Liu

Many Actinidia cultivars are characterized by anthocyanin accumulation, specifically in the inner pericarp, but the underlying regulatory mechanism remains elusive. Here we report two interacting transcription factors, AcMYB123 and AcbHLH42, that regulate tissue‐specific anthocyanin biosynthesis in the inner pericarp of Actinidia chinensis cv. Hongyang. Through transcriptome profiling analysis we identified five MYB and three bHLH transcription factors that were upregulated in the inner pericarp. We show that the combinatorial action of two of them, AcMYB123 and AcbHLH42, is required for activating promoters of AcANS and AcF3GT1 that encode the dedicated enzymes for anthocyanin biosynthesis. The presence of anthocyanin in the inner pericarp appears to be tightly associated with elevated expression of AcMYB123 and AcbHLH42. RNA interference repression of AcMYB123, AcbHLH42, AcF3GT1 and AcANS in ‘Hongyang’ fruits resulted in significantly reduced anthocyanin biosynthesis. Using both transient assays in Nicotiana tabacum leaves or Actinidia arguta fruits and stable transformation in Arabidopsis, we demonstrate that co‐expression of AcMYB123 and AcbHLH42 is a prerequisite for anthocyanin production by activating transcription of AcF3GT1 and AcANS or the homologous genes. Phylogenetic analysis suggests that AcMYB123 or AcbHLH42 are closely related to TT2 or TT8, respectively, which determines proanthocyanidin biosynthesis in Arabidopsis, and to anthocyanin regulators in monocots rather than regulators in dicots. All these experimental results suggest that AcMYB123 and AcbHLH42 are the components involved in spatiotemporal regulation of anthocyanin biosynthesis specifically n the inner pericarp of kiwifruit.

许多栽培种猕猴桃具有很高的花青素积累，尤其是在内果皮组织中，但潜在的分子调控机制还不清楚。本文，作者报道了两个互作的转录因子AcMYB123和AcbHLH42调控中华猕猴桃（品种：红阳）内果皮上组织特异性的花青素积累。通过转录组学的分析，作者发现了有五个MYB和三个bHLH转录因子在内果皮中上调表达。作者的研究显示，其中两个转录因子，即AcMYB123和AcbHLH42的互作对于激活花青素生物合成相关酶AcANS和AcF3GT1的表达是必需的。猕猴桃内果皮中的花青素含量显然与AcMYB123和AcbHLH42基因表达量的增加紧密相关。利用RNA干扰抑制红阳中AcMYB123、AcbHLH42、AcF3GT1和AcANS基因的表达能够显著减少花青素的生物合成。利用烟草叶片或者软枣猕猴桃果实进行瞬间表达试验以及拟南芥进行稳定遗传转化试验均证明了AcMYB123和AcbHLH42的共表达是花青素产量的先决条件，AcMYB123和AcbHLH42通过激活AcF3GT1和AcANS基因或者其同源基因的转录增加花青素的合成。进化分析显示AcMYB123与TT2比较接近，AcbHLH42与TT8比较接近，而这两个基因是拟南芥中决定原花青素合成的关键基因；另外，相比于双子叶植物，AcMYB123和AcbHLH42更加接近单子叶植物中的花青素调控基因。综上，本文的研究结果显示AcMYB123和AcbHLH42参与了猕猴桃内果皮中组织特异性花青素合成的时空调控。

通讯：刘永胜（http://life.scu.edu.cn/webContent.asp?articleId=984&type=shiziduiwu）

个人简介：1994年，四川农业大学，博士。

研究方向：番茄、猕猴桃基因组和功能基因组学研究；表观遗传；次生代谢调控与品质改良的基因工程技术。

doi: https://doi.org/10.1111/tpj.14330

Journal: the plant journal

First Published: March 26, 2019