The 70-kDa heat shock protein (HSP70) is a molecular chaperone that plays an important role in the response of plants to abiotic stress, but the function and molecular mechanism of HSP70 in the cotton drought stress response are unclear. In this study, the HSP70-encoding gene GhHSP70-26, which belongs to the cytoplasmic HSP70 subgroup, was cloned from upland cotton (Gossypium hirsutum L.). The transcript level of GhHSP70-26 in cotton leaves was higher than that in cotton stems and roots. GhHSP70-26 was found to respond at the transcriptional level to polyethylene glycol (PEG) and abscisic acid (ABA) treatment and to cold, salt, and heat stress, and its transcript level was positively correlated with the drought resistance of different cotton varieties. Heterologous overexpression of the GhHSP70-26 gene improved the drought resistance of transgenic tobacco compared with that of wild-type (WT) tobacco, and the transgenic tobacco plants were characterized by low leaf wilting, high survival, low leaf water loss, increased root length and high chlorophyll content. Moreover, the transgenic tobacco plants overexpressing GhHSP70-26 had higher proline contents, higher superoxide dismutase (SOD) and peroxidase (POD) enzyme activities, and lower malondialdehyde (MDA) and reactive oxygen species (ROS) contents than the WT tobacco plants. The transcript levels of the stress response-related genes NtLEA, NtERD10D, NtPOD, NtSOD, and NtNCED3-1 in transgenic tobacco overexpressing GhHSP70-26 were significantly higher than those in WT tobacco. In contrast, under drought stress, unlike the results obtained with the pTRV2 empty vector (EV)-transformed and WT cotton plants, the use of virus-induced gene silencing (VIGS) technology to silence the GhHSP70-26 gene in cotton resulted in plants with severely wilted leaves, an increased water loss rate, a higher MDA content, and higher relative electrical conductivity (REC). Furthermore, yeast one-hybrid assays showed that GhbZIP43 and GhHSF8 bind to ABA-responsive elements (ABREs) and heat shock elements (HSEs) in the GhHSP70-26 promoter, respectively. Moreover, yeast two-hybrid, bimolecular fluorescence complementation and luciferase complementation assays showed that the GhHSP70-26 protein interacts with the ascorbate peroxidase (APX) GhAPX2 protein. These results indicate that by reducing the degrees of cell membrane damage and cellular damage caused by ROS stress, the GhHSP70-26 protein plays a positive role in the response of plants to drought stress.

70-kDa热休克蛋白（HSP70）是一种分子伴侣，在植物对非生物胁迫的响应中起重要作用，但HSP70在棉花干旱胁迫响应中的功能和分子机制尚不清楚。本研究从陆地棉（Gossypium hirsutum L.）中克隆了HSP70编码基因GhHSP70-26，属于细胞质HSP70亚群。GhHSP70-26在棉花叶片中的转录水平高于在棉花茎和根中的转录水平。GhHSP70-26发现在转录水平上对聚乙二醇（PEG）和脱落酸（ABA）处理以及冷、盐和热胁迫有响应，其转录水平与不同棉花品种的抗旱性呈正相关。与野生型 (WT) 烟草相比，GhHSP70-26基因的异源过表达提高了转基因烟草的抗旱性，转基因烟草植株的特点是低叶枯萎、高存活率、低叶失水、增加根长和高叶绿素含量。此外，过表达GhHSP70-26的转基因烟草植物与WT烟草植物相比，具有更高的脯氨酸含量，更高的超氧化物歧化酶（SOD）和过氧化物酶（POD）酶活性，以及​​更低的丙二醛（MDA）和活性氧（ROS）含量。过量表达GhHSP70-26 的转基因烟草中应激反应相关基因NtLEA、NtERD10D、NtPOD、NtSOD和NtNCED3-1的转录水平显着高于 WT 烟草中的转录水平。相比之下，在干旱胁迫下，与 pTRV2 空载体 (EV) 转化和 WT 棉花植物获得的结果不同，使用病毒诱导基因沉默 (VIGS) 技术使GhHSP70-26沉默棉花中的基因导致植物叶片严重枯萎、失水率增加、MDA 含量更高、相对电导率 (REC) 更高。此外，酵母单杂交试验表明，GhbZIP43 和 GhHSF8分别与GhHSP70-26启动子中的 ABA 响应元件 (ABRE) 和热休克元件 (HSE) 结合。此外，酵母双杂交、双分子荧光互补和荧光素酶互补测定表明 GhHSP70-26 蛋白与抗坏血酸过氧化物酶 (APX) GhAPX2 蛋白相互作用。这些结果表明，GhHSP70-26蛋白通过降低ROS胁迫引起的细胞膜损伤和细胞损伤程度，在植物对干旱胁迫的响应中发挥积极作用。