The Arabidopsis PLAT Domain Protein1 Is Critically Involved in Abiotic Stress Tolerance

Despite the completion of the Arabidopsis genome sequence, for only a relatively low percentage of the encoded proteins experimental evidence concerning their function is available. Plant proteins that harbour a single PLAT (Polycystin, Lipoxygenase, Alpha-toxin and Triacylglycerol lipase) domain and belong to the PLAT-plant-stress protein family are ubiquitously present in monocot and dicots. However, the function of PLAT-plant-stress proteins is still poorly understood. Therefore, we have assessed the function of the uncharacterised Arabidopsis PLAT-plant-stress family members through a combination of functional genetic and physiological approaches. PLAT1 overexpression conferred increased abiotic stress tolerance, including cold, drought and salt stress, while loss-of-function resulted in opposite effects on abiotic stress tolerance. Strikingly, PLAT1 promoted growth under non-stressed conditions. Abiotic stress treatments induced PLAT1 expression and caused expansion of its expression domain. The ABF/ABRE transcription factors, which are positive mediators of abscisic acid signalling, activate PLAT1 promoter activity in transactivation assays and directly bind to the ABRE elements located in this promoter in electrophoretic mobility shift assays. This suggests that PLAT1 represents a novel downstream target of the abscisic acid signalling pathway. Thus, we showed that PLAT1 critically functions as positive regulator of abiotic stress tolerance, but also is involved in regulating plant growth, and thereby assigned a function to this previously uncharacterised PLAT domain protein. The functional data obtained for PLAT1 support that PLAT-plant-stress proteins in general could be promising targets for improving abiotic stress tolerance without yield penalty.尽管拟南芥（Arabidopsis）基因组测序已然完成，但仅有占比相对较低的编码蛋白拥有与其功能相关的实验验证数据。含有单个PLAT（Polycystin, Lipoxygenase, Alpha-toxin and Triacylglycerol lipase）结构域且隶属于PLAT-植物-胁迫蛋白家族的植物蛋白，在单子叶与双子叶植物中广泛分布。然而，目前学界对PLAT-植物-胁迫蛋白的功能仍知之甚少。 为此，我们结合功能遗传学与生理学实验手段，对尚未被功能表征的拟南芥PLAT-植物-胁迫蛋白家族成员的功能展开了评估。实验结果显示，PLAT1的过表达可提升植株的非生物胁迫（abiotic stress）耐受性，涵盖低温、干旱与盐胁迫；而PLAT1功能缺失突变则会对植株的非生物胁迫耐受性产生相反影响。值得注意的是，PLAT1在非胁迫条件下可促进植株生长。 非生物胁迫处理能够诱导PLAT1的基因表达，并使其表达范围发生扩展。作为脱落酸（abscisic acid）信号通路的正向介导因子，ABF/ABRE转录因子在反式激活实验中可激活PLAT1启动子的转录活性，且在电泳迁移率变动分析中可直接结合该启动子内的ABRE顺式作用元件。上述结果表明，PLAT1是脱落酸信号通路的一类新型下游靶标蛋白。 综上，本研究证实PLAT1可作为正向调控因子关键调控非生物胁迫耐受性，同时亦参与植物生长调控，从而为这一此前未被功能表征的PLAT结构域蛋白明确了生物学功能。本次针对PLAT1获得的功能实验数据，支持PLAT-植物-胁迫蛋白家族整体可作为提升作物非生物胁迫耐受性且不会伴随产量损耗的潜在靶点。