Zhuo Chunliu, Wang Ting, Guo Zhenfei, Lu Shaoyun
State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, Guangdong Engineering Research Center for Grassland Science, College of Life Sciences, South China Agricultural University, Guangzhou, 510642, China.
College of Grassland Science, Nanjing Agricultural University, Nanjing, 210095, China.
BMC Plant Biol. 2016 Jun 14;16(1):138. doi: 10.1186/s12870-016-0814-4.
Plasma membrane intrinsic proteins (PIPs), which belong to aquaporins (AQPs) superfamily, are subdivided into two groups, PIP1 and PIP2, based on sequence similarity. Several PIP2s function as water channels, while PIP1s have low or no water channel activity, but have a role in water permeability through interacting with PIP2. A cold responsive PIP2 named as MfPIP2-7 was isolated from Medicago falcata (hereafter falcata), a forage legume with great cold tolerance, and transgenic tobacco plants overexpressing MfPIP2-7 were analyzed in tolerance to multiple stresses including freezing, chilling, and nitrate reduction in this study.
MfPIP2-7 transcript was induced by 4 to 12 h of cold treatment and 2 h of abscisic acid (ABA) treatment. Pretreatment with inhibitor of ABA synthesis blocked the cold induced MfPIP2-7 transcript, indicating that ABA was involved in cold induced transcription of MfPIP2-7 in falcata. Overexpression of MfPIP2-7 resulted in enhanced tolerance to freezing, chilling and NO3 (-) deficiency in transgenic tobacco (Nicotiana tabacum L.) plants as compared with the wild type. Moreover, MfPIP2-7 was demonstrated to facilitate H2O2 diffusion in yeast. Higher transcript levels of several stress responsive genes, such as NtERD10B, NtERD10C, NtDREB1, and 2, and nitrate reductase (NR) encoding genes (NtNIA1, and NtNIA2) were observed in transgenic plants as compared with the wild type with dependence upon H2O2. In addition, NR activity was increased in transgenic plants, which led to alterations in free amino acid components and concentrations.
The results suggest that MfPIP2-7 plays an important role in plant tolerance to freezing, chilling, and NO3 (-) deficiency by promoted H2O2 diffusion that in turn up-regulates expression of NIAs and multiple stress responsive genes.
质膜内在蛋白（PIPs）属于水通道蛋白（AQPs）超家族，根据序列相似性可分为两组，即PIP1和PIP2。几种PIP2发挥水通道的功能，而PIP1的水通道活性较低或没有水通道活性，但通过与PIP2相互作用在水通透性方面发挥作用。从具有很强耐寒性的豆科牧草黄花苜蓿（以下简称黄花苜蓿）中分离出一种名为MfPIP2 - 7的冷响应PIP2，并在本研究中对过表达MfPIP2 - 7的转基因烟草植株进行了包括冷冻、冷害和硝酸盐还原在内的多种胁迫耐受性分析。
MfPIP2 - 7转录本在4至12小时的冷处理和2小时的脱落酸（ABA）处理下被诱导。用ABA合成抑制剂预处理可阻断冷诱导的MfPIP2 - 7转录本，表明ABA参与了黄花苜蓿中冷诱导的MfPIP2 - 7转录。与野生型相比，MfPIP2 - 7的过表达导致转基因烟草（Nicotiana tabacum L.）植株对冷冻、冷害和NO3 (-)缺乏的耐受性增强。此外，已证明MfPIP2 - 7促进酵母中H2O2的扩散。与野生型相比，在转基因植株中观察到几种胁迫响应基因（如NtERD10B、NtERD10C、NtDREB1和2）以及硝酸盐还原酶（NR）编码基因（NtNIA1和NtNIA2）的转录水平更高，且依赖于H2O2。此外，转基因植株中NR活性增加，这导致游离氨基酸成分和浓度发生变化。
结果表明，MfPIP2 - 7通过促进H2O2扩散在植物对冷冻、冷害和NO3 (-)缺乏的耐受性中发挥重要作用，进而上调NIA和多种胁迫响应基因的表达。
