A tomato B‐ox protein SlBBX20 modulates carotenoid biosynthesis by directly activating PHYTOENE SYNTHASE 1, and is targeted for 26S proteasome‐mediated degradation

First author: Cheng Xiong; Affiliations: Huazhong Agricultural University (华中农业大学): Wuhan, China

Corresponding author: Taotao Wang (王涛涛)

Carotenoids play important roles in many biological processes, such as light harvesting (光捕获), photoprotection (光防护) and visual attraction (视觉吸引) in plants. However, the regulation of carotenoid biosynthesis is still not fully understood. Here, we demonstrate that SlBBX20, a B‐ox (BBX) zinc‐finger transcription factor, is a positive regulator of carotenoid accumulation in tomato (Solanum lycopersicum). Overexpression of SlBBX20 leads to dark green fruits and leaves and higher levels of carotenoids relative to the wild‐ ype. Interactions between SlBBX20 and DE‐ETIOLATED 1 (SlDET1) lead to the ubiquitination and 26S proteasome‐mediated degradation of SlBBX20. Moreover, deficiencies in the components of the CUL4‐DDB1‐DET1 complex enhanced the stability of the SlBBX20 protein. Thus, we conclude that SlBBX20 is a substrate of the CUL4‐DDB1‐DET1 E3 ligase. SlBBX20 can activate the expression of PHYTOENE SYNTHASE 1, encoding a key enzyme in carotenoid biosynthesis, by directly binding to a G‐ox motif in its promoter, which results in the elevated levels of carotenoids in SlBBX20 overexpression lines. We identified a key regulator of carotenoid biosynthesis and demonstrated that the stability of SlBBX20 is regulated by ubiquitination. These findings provide us a new target for the genetic improvement of the nutritional quality of tomato fruit.

类胡萝卜素在植物中的诸多生物进程中扮演重要作用，比如光捕获、光保护及视觉吸引。然而，目前对于类胡萝卜素生物合成的分子机制了解的还不够彻底。本文揭示了番茄一个B‐ox锌指转录因子BBX20对于类胡萝卜素的积累具有正向的调控作用。在番茄中过表达SlBBX20基因会出现墨绿色的果实和叶片，并且相对于野生型，转基因植株中类胡萝卜素的含量更高。SlBBX20与SlDET1之间的互作会导致SlBBX20的泛素化和26S蛋白酶体所介导的降解。此外，CUL4‐DDB1‐DET1复合物中某个组份的缺陷增强了SlBBX20蛋白的稳定性。因此，作者认为SlBBX20是CUL4‐DDB1‐DET1 E3连接酶的底物。SlBBX20蛋白能够通过直接结合到八氢番茄红素合成酶PHYTOENE SYNTHASE 1基因启动子区的G‐ox基序促进该类胡萝卜素生物合成关键酶的表达，进而导致了SlBBX20过表达植株中的类胡萝卜素水平的提升。本文的研究鉴定了类胡萝卜素生物成的一个关键调控基因，并揭示了SlBBX20的稳定性收到泛素化的调控。这些发现为番茄果实的营养质量改良提供了新的遗传靶标。

通讯：王涛涛 (http://chfs.hzau.edu.cn/info/1032/1172.htm)

个人简介：2000年，华中农业大学，学士；2006年，华中农业大学，博士；2007年，荷兰Wageningen大学，合作研究；2014-2016年，美国Texas A&M University，访问学者。

研究方向：主要从事番茄生物与非生物逆境抗性基因克隆，功能鉴定和分子机理研究；番茄，甘蓝等作物的种质创新与新品种选育工作。

doi: https://doi.org/10.1111/nph.15373

Journal: New Phytologist

First Published: 13 August, 2018

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