丛枝菌根真菌通过上调根系及自身水孔蛋白基因表达提高玉米抗旱性

 在模拟干旱条件下, 研究了接种丛枝菌根(AM)真菌Glomus intraradices对玉米(Zea mays)根部13种质膜水孔蛋白基因表达的影响, 同时观测了AM真菌自身水孔蛋白基因的表达情况。结果表明, 干旱条件下, 除Zm PIP1;3、Zm PIP1;4、Zm PIP1;5和Zm PIP2;2之外的接种处理能显著提高根部其他8种质膜水孔蛋白基因的表达(Zm PIP2;7表达量未检测出), 并且AM真菌菌丝中水孔蛋白基因GintAQP1表达也显著增强。与此同时, 接种处理明显改善了植物水分状况, 提高了叶片水势。AM真菌增强宿主植物根部及自身的水孔蛋白基因的表达对于提高植物抗旱性具有潜在的重要贡献。

Arbuscular mycorrhizal fungi improving drought tolerance of maize plants by up-regulation of aquaporin gene expressions in roots and the fungi themselves

Aims It has been well demonstrated that arbuscular mycorrhizal (AM) fungi can improve water balance and drought tolerance of host plants under drought stress. However, controversy still exists in mechanisms underlying the mycorrhizal functions. For example, in different experiments AM fungi could up- or down-regulate plant aquaporin gene expression. Furthermore, little information is available on the expression of aquaporin genes in AM fungi under drought stress and its contribution to plant drought tolerance. We investigated the effects of an AM fungus, Glomus intraradices, on expression of a plasma membrane intrinsic protein (PIP) gene family containing 13 PIP genes in maize roots and one aquaporin gene from the AM fungus under simulated drought conditions. Our objectives were to systematically investigate the aquaporin gene expression in the mycorrhizal association in response to drought stress and to help understand the molecular basis for drought tolerance of AM symbiosis.
Methods Maize plants inoculated with/without AM fungus G. intraradices were grown under different water regimes in a controlled-environment climate chamber for 42 days. At harvest, the leaf water potential (Ψ) was determined with an SKPM 1400 pressure chamber, and then shoots and roots were collected and carefully cleaned with tap water. Three grams of mixed roots were used to estimate the percentage root colonization after clearing with 10% KOH and staining with 0.05% (v/v) trypan blue in lactic acid. One gram of mixed roots was used to extract total RNA by using TRIZOL to synthesize cDNA. Real-time PCR analysis was performed to estimate the expression of Zm PIP genes and GintAQP1. Shoots and the rest of roots were dried at 105 °C for 10 min and 80 °C for 48 h to obtain dry weights. About 0.2 g of dried shoots or roots was digested by HNO₃ for 12 h. The P concentration was recorded by using microplate reader spectra at the wavelength of 820 nm. Experimental data were subjected to statistical analysis using SPSS 13.0.
Important findings Under drought stress, inoculation with AM fungus significantly enhanced expression of eight PIP genes except for Zm PIP1;3, Zm PIP1;4 Zm PIP1;5 and Zm PIP2;2 (Zm PIP2;7 expression not detected), and drought stress also enhanced expression of GintAQP1 cloned from hyphae of G. intraradices. Enhanced aquaporin gene expression was beneficial to improvement of plant water status and increase of leaf water potential.