南湖新闻网讯（通讯员 宋杰 李春龙）近日，我校园艺植物生物学教育部重点实验室刘继红教授团队在New Phytologist上发表了题为“SnRK2.4-mediated phosphorylation of ABF2 regulates ARGININE DECARBOXYLASE expression and putrescine accumulation under drought stress”的研究论文。该研究在已有研究的基础上，进一步揭示了干旱胁迫响应分子模块SnRK2.4-ABF2-ADC调控腐胺合成应答干旱的功能和分子机制。
精氨酸脱羧酶（ADC）介导的腐胺生物合成在植物非生物胁迫响应中起着至关重要的作用。SnRK2（SNF1-related protein kinases 2s）和ABF（ABA-response element (ABRE) binding factors）是ABA信号通路中参与干旱胁迫响应的核心组成部分。课题组前期研究发现，枳（Poncirus trifoliata）PtrADC在干旱胁迫下发挥正调控作用。然而，SnRK2和ABF是否以及如何调控PtrADC来调节干旱胁迫下腐胺积累的机制尚不清楚。
SnRK2.4-ABF2-ADC分子模块调控腐胺合成模式图
课题组以PtrADC为诱饵开展酵母单杂交筛选文库，获得了一个转录因子PtrABF2，并通过Y1H、EMSA、CHIP-PCR和LUC等实验验证了PtrABF2能特异性结合PtrADC启动子上的ABRE元件并激活该基因表达，随后通过转基因技术表明PtrABF2通过调控PtrADC表达和腐胺合成积累从而增强枳抗旱性。研究人员进一步鉴定到PtrSnRK2家族成员PtrSnRK2.4受ABA强烈诱导，发现PtrSnRK2.4可以与PtrABF2互作并磷酸化PtrABF2，质谱分析表明磷酸化位点位于第93号丝氨酸位点（Ser93）。利用双荧光素酶、凝胶迁移、转录激活等实验分析表明PtrABF2对其靶基因PtrADC启动子的转录结合能力依赖于PtrSnRK2.4的磷酸化修饰。随后通过转基因和生理表型研究，证明PtrSnRK2.4正调控枳抗旱性，且该过程与多胺的合成紧密相关。
综上所述，该研究提出了SnRK2.4-ABF2-ADC模块调控枳干旱诱导腐胺合成与积累的分子模块，阐述了PtrABF2在干旱胁迫下的转录调控机制，以及上游蛋白激酶PtrSnRK2.4磷酸化PtrABF2介导植物腐胺合成与积累过程中的重要作用。研究建立了SnRK2.4-ABF2-ADC模块与多胺合成的联系，从而阐明了干旱诱导ADC表达和腐胺积累的分子生物学基础，解析了该生理现象的信号通路和分子机制，同时也丰富了干旱诱导植物代谢改变的理论研究。
我校园艺林学学院刘继红教授为该论文通讯作者，已毕业博士生宋杰为该论文第一作者，李春龙教授和安徽农业大学孙培培老师也参与了研究工作。该研究依托华中农业大学园艺植物生物学教育部重点实验室平台，受到国家重点研发计划项目和国家自然科学基金资助。
审核人：刘继红
【英文摘要】
Arginine decarboxylase (ADC)-mediated putrescine (Put) biosynthesis plays an important role in plant abiotic stress response. SnRK2 (SNF1-related protein kinases 2) and ABF (ABA-response element binding factors) are core components of ABA signaling pathway involved in drought stress response. We previously reported that ADC of Poncirus trifoliata (PtrADC) functions in drought tolerance. However, whether and how SnRK2 and ABF regulate PtrADC to modulate putrescine accumulation under drought stress remains largely unclear.
Herein, we employed a set of physiological, biochemical, and molecular approaches to reveal that a protein complex composed of PtrSnRK2.4 and PtrABF2 modulates putrescine biosynthesis and drought tolerance by directly regulating PtrADC.
PtrABF2 was up-regulated by dehydration in an ABA-dependent manner. PtrABF2 activated PtrADC by directly binding to its promoter and positively regulated drought tolerance via modulating putrescine accumulation. PtrSnRK2.4 interacts with and phosphorylates PtrABF2 at Ser93. PtrSnRK2.4-mediated PtrABF2 phosphorylation is essential for its transcriptional regulation of PtrADC. Besides, PtrSnRK2.4 was shown to play a positive role in drought tolerance and putrescine synthesis.
Taken together, this study sheds new light on the regulatory module SnRK2.4-ABF2-ADC responsible for fine-tuning putrescine accumulation under drought stress, which advances our understanding on transcriptional regulation of putrescine synthesis and plant drought resistance mechanism.
论文链接： https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.18526
