Abstract
Aquaporins (AQPs) are one diverse family of membrane channel proteins that play crucial regulatory roles in plant stress physiology. However, the heat stress responsiveness of AQP genes in soybean remains poorly understood. In this study, 75 non-redundant AQP encoding genes were identified in soybean. Multiple sequence alignments showed that all GmAQP proteins possessed the conserved regions, which contained 6 trans-membrane domains (TM1 to TM6). Different GmAQP members consisted of distinct Asn-Pro-Ala (NPA) motifs, aromatic/arginine (ar/R) selectivity filters and Froger’s positions (FPs). Phylogenetic analyses distinguished five sub-families within these GmAQPs: 24 GmPIPs, 24 GmTIPs, 17 GmNIPs, 8 GmSIPs, and 2 GmXIPs. Promoter cis-acting elements analyses revealed that distinct number and composition of heat stress and hormone responsive elements existed in different promoter regions of GmAQPs. QRT-PCR assays demonstrated that 12 candidate GmAQPs with relatively extensive expression in various tissues or high expression levels in root or leaf exhibited different expression changes under heat stress and hormone cues (abscisic acid (ABA), l-aminocyclopropane-l-carboxylic acid (ACC), salicylic acid (SA) and methyl jasmonate (MeJA)). Furthermore, the promoter activity of one previously functionally unknown AQP gene-GmTIP2;6 was investigated in transgenic Arabidopsis plants. The beta-glucuronidase (GUS) activity driven by the promoter of GmTIP2;6 was strongly induced in the heat- and ACC-treated transgenic plants and tended to be accumulated in the hypocotyls, vascular bundles, and leaf trichomes. These results will contribute to uncovering the potential functions and molecular mechanisms of soybean GmAQPs in mediating heat stress and hormone signal responses.
Highlights
Aquaporins (AQPs), known as membrane channel proteins, transport water as well as other small solutes (AQPs)
Based on the protein sequence homology and membrane localization, plant AQPs are divided into five sub-families: plasma membrane intrinsic proteins (PIPs), tonoplast intrinsic proteins (TIPs), NOD26-like intrinsic proteins (NIPs), small basic intrinsic proteins (SIPs), and the unrecognized X intrinsic proteins (XIPs) [8]
From the recently-updated soybean genome database Phytozome V12.1, 75 putative GmAQPs were identified based on HMM profile, KEGG orthology, BlastP, and BlastN searches (Table 1)
Summary
Aquaporins (AQPs), known as membrane channel proteins, transport water as well as other small solutes (AQPs). AQPs belong to an ancient, abundant, and highly diversified protein super-family [2,3,4,5,6,7]. Transcript profiles or gene function analyses of AQPs from many plant species, such as Arabidopsis, rice, barley, sorghum, cassava, soybean, and potato, demonstrated that they were associated with drought, cold, salt, silicon, or ABA stress [11,12,13,14,15,16,17]. TaTIPs respond to the combined heat and drought stresses, based on the representation of expressed sequence tags (ESTs) in wheat grain-related cDNA libraries [18]. In Arabidopsis, AtPIPs were highly up-regulated due to combined heat-drought stress [23]. Functions and mechanisms of soybean AQPs in heat stress tolerance remain obscure
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