Miao Miao, Shi Ximiao, Zheng Xiangzi, Wu Binghua, Miao Ying
Fujian Provincial Key Laboratory of Plant Functional Biology, College of Life Sciences, Fujian Agriculture & Forestry University, Fuzhou, China.
College of Horticulture, Fujian Agriculture and Forestry University, Fuzhou, 350002, China.
BMC Plant Biol. 2024 Apr 22;24(1):305. doi: 10.1186/s12870-024-05002-x.
Aquaporins (AQPs) facilitate water diffusion across biological membranes and are involved in all phases of growth and development. Small and basic intrinsic proteins (SIPs) belong to the fourth subfamily of the plant AQPs. Although SIPs are widely present in higher plants, reports on SIPs are limited. Rice is one of the major food crops in the world, and water use is an important factor affecting rice growth and development; therefore, this study aimed to provide information relevant to the function and environmental response of the rice SIP gene family.
The rice (Oryza sativa L. japonica) genome encodes two SIP-like genes, OsSIP1 and OsSIP2, whose products are predominantly located in the endoplasmic reticulum (ER) membrane but transient localization to the plasma membrane is not excluded. Heterologous expression in a yeast aquaglyceroporin-mutant fps1Δ showed that both OsSIP1 and OsSIP2 made the cell more sensitive to KCl, sorbitol and HO, indicating facilitated permeation of water and hydrogen peroxide. In addition, the yeast cells expressing OsSIP2 were unable to efflux the toxic methylamine taken up by the endogenous MEP permeases, but OsSIP1 showed subtle permeability to methylamine, suggesting that OsSIP1 may have a wider conducting pore than OsSIP2. Expression profiling in different rice tissues or organs revealed that OsSIP1 was expressed in all tissues tested, whereas OsSIP2 was preferentially expressed in anthers and weakly expressed in other tissues. Consistent with this, histochemical staining of tissues expressing the promoter-β-glucuronidase fusion genes revealed their tissue-specific expression profile. In rice seedlings, both OsSIPs were upregulated to varied levels under different stress conditions, including osmotic shock, high salinity, unfavorable temperature, redox challenge and pathogen attack, as well as by hormonal treatments such as GA, ABA, MeJA, SA. However, a reduced expression of both OsSIPs was observed under dehydration treatment.
Our results suggest that SIP-like aquaporins are not restricted to the ER membrane and are likely to be involved in unique membrane functions in substrate transport, growth and development, and environmental response.
水通道蛋白（AQPs）促进水在生物膜上的扩散，并参与生长和发育的各个阶段。小分子碱性内在蛋白（SIPs）属于植物水通道蛋白的第四亚家族。尽管SIPs广泛存在于高等植物中，但关于SIPs的报道有限。水稻是世界主要粮食作物之一，水分利用是影响水稻生长发育的重要因素；因此，本研究旨在提供与水稻SIP基因家族功能和环境响应相关的信息。
水稻（Oryza sativa L. japonica）基因组编码两个类SIP基因，OsSIP1和OsSIP2，其产物主要位于内质网（ER）膜上，但不排除瞬时定位到质膜。在酵母水甘油通道蛋白突变体fps1Δ中的异源表达表明，OsSIP1和OsSIP2都使细胞对KCl、山梨醇和HO更敏感，表明促进了水和过氧化氢的渗透。此外，表达OsSIP2的酵母细胞无法排出内源性MEP通透酶吸收的有毒甲胺，但OsSIP1对甲胺表现出微弱的通透性，这表明OsSIP1可能比OsSIP2具有更宽的传导孔。在不同水稻组织或器官中的表达谱分析表明，OsSIP1在所有测试组织中均有表达，而OsSIP2在花药中优先表达，在其他组织中弱表达。与此一致，表达启动子-β-葡萄糖醛酸酶融合基因的组织的组织化学染色揭示了它们的组织特异性表达谱。在水稻幼苗中，在不同胁迫条件下，包括渗透冲击、高盐度、不利温度、氧化还原挑战和病原体攻击，以及通过GA、ABA、MeJA、SA等激素处理，两种OsSIPs均上调至不同水平。然而，在脱水处理下观察到两种OsSIPs的表达均降低。
我们的结果表明，类SIP水通道蛋白不限于内质网膜，可能参与底物运输、生长发育和环境响应中的独特膜功能。
