ZmPBF and ZmGAMYB transcription factors independently transactivate the promoter of the maize (Zea mays) β‐carotene hydroxylase 2 gene

First author: Xin Jin; Affiliations: University of Lleida‐Agrotecnio Center (莱里达大学阿格罗特尼奥中心): Lleida, Spain

Corresponding author: Changfu Zhu

The maize (Zea mays) enzyme β‐carotene hydroxylase 2 (ZmBCH2; β‐胡萝卜素羟化酶) controls key steps in the conversion of β‐carotene to zeaxanthin (玉米黄素) in the endosperm. The ZmBCH2 has an endosperm‐preferred and developmentally regulated expression profile but the detailed regulatory mechanism is unknown. To gain insight into the regulation of ZmBCH2, we isolated 2036 bp of the 5′‐flanking region which contains the 263‐p 5′‐untranslated region (5′‐UTR) including the first intron. We linked this to the β‐glucuronidase reporter gene (β-葡萄糖醛酸酶报告基因) gusA. We found that high‐level expression of gusA in rice seeds requires the 5′‐UTR for enhanced activation. Truncated variants of the ZmBCH2 promoter retained their seed‐preferred expression profile as long as a prolamin (醇溶蛋白) box and AACA motif were present. We identified candidate genes encoding the corresponding transcription factors (ZmPBF and ZmGAMYB) and confirmed that their spatiotemporal expression profiles are similar to ZmBCH2. Both ZmPBF and ZmGAMYB can transactivate (反式激活) ZmBCH2 expression in maize endosperm. To eliminate potential confounding effects in maize, we characterized the regulation of the minimal promoter region of ZmBCH2 in transgenic rice. This revealed that ZmPBF and ZmGAMYB independently transactivate the ZmBCH2 promoter. The mechanism that underpins our data provides an exciting new strategy for the control of target gene expression in engineered plants.

玉米的β‐胡萝卜素羟化酶ZmBCH2控制β‐胡萝卜素向玉米黄素的转变。ZmBCH2基因优先在胚乳中表达，并且与胚乳的发育相关，但其具体的调控机制还不清楚。为了研究ZmBCH2基因的分子调控机制，作者在本文中克隆了ZmBCH2基因5′侧翼区域的2036bp序列，包含了263bp的5′‐UTR序列，包含了第一个内涵子。作者在克隆到的序列后面连上了β-葡萄糖醛酸酶报告基因gusA并转到了水稻里面，发现gusA在水稻种子里面的高表达需要5′‐UTR来增强激活。ZmBCH2启动子的截断变异研究显示只要保留醇溶蛋白盒和AACA基序，其在种子中表达的特性就不会发生改变。作者鉴定到了两个转录因子ZmPBF和ZmGAMYB，并且发现这两个转录因子的表达模式与ZmBCH2基因类似。ZmPBF和ZmGAMYB能够在玉米胚乳中反式激活ZmBCH2基因的表达。为了消除玉米中其他潜在因素的影响，作者在转基因水稻中研究了ZmBCH2基因发挥作用的最短启动子序列，结果显示ZmPBF和ZmGAMYB相互独立反式激活ZmBCH2基因启动子。本文的研究为在转基因植物中研究靶基因表达调控提供了一个新的策略。

doi: https://doi.org/10.1111/nph.15614

Journal: New Phytologist

First Published: 29 November, 2018