Abstract
Waterlogging is a significant environmental constraint to crop production, and a better understanding of plant responses is critical for the improvement of crop tolerance to waterlogged soils. Aquaporins (AQPs) are a class of channel-forming proteins that play an important role in water transport in plants. This study aimed to examine the regulation of AQP genes under waterlogging stress and to characterize the genetic variability of AQP genes in sorghum (Sorghum bicolor). Transcriptional profiling of AQP genes in response to waterlogging stress in nodal root tips and nodal root basal regions of two tolerant and two sensitive sorghum genotypes at 18 and 96 h after waterlogging stress imposition revealed significant gene-specific pattern with regard to genotype, root tissue sample, and time point. For some tissue sample and time point combinations, PIP2-6, PIP2-7, TIP2-2, TIP4-4, and TIP5-1 expression was differentially regulated in tolerant compared to sensitive genotypes. The differential response of these AQP genes suggests that they may play a tissue specific role in mitigating waterlogging stress. Genetic analysis of sorghum revealed that AQP genes were clustered into the same four subfamilies as in maize (Zea mays) and rice (Oryza sativa) and that residues determining the AQP channel specificity were largely conserved across species. Single nucleotide polymorphism (SNP) data from 50 sorghum accessions were used to build an AQP gene-based phylogeny of the haplotypes. Phylogenetic analysis based on single nucleotide polymorphisms of sorghum AQP genes placed the tolerant and sensitive genotypes used for the expression study in distinct groups. Expression analyses suggested that selected AQPs may play a pivotal role in sorghum tolerance to water logging stress. Further experimentation is needed to verify their role and to leverage phylogenetic analyses and AQP expression data to improve waterlogging tolerance in sorghum.
Highlights
Aquaporins are integral membrane proteins that form channels that allow water to move from one plant compartment to another
Unlike plasma membrane intrinsic protein (PIP), tonoplast intrinsic protein (TIP), NOD26-like intrinsic protein (NIP), and small basic protein (SIP) which are present in all land plants, GIPs and hybrid intrinsic proteins (HIPs) have only been identified in algae and moss, and X (unrecognized) intrinsic proteins (XIPs) only in moss and several dicots (Danielson and Johanson, 2008; Venkatesh et al, 2013; Zhang et al, 2013)
Analyses of RNAseq data (Supplementary Table S2, Kadam et al unpublished) indicated that transcript abundance of the SbAQP genes encoding PIP1-6, PIP2-5, PIP2-6, PIP2-7, TIP2-1, TIP2-2, TIP4-4, TIP5-1, and NIP4-1 was influenced by waterlogging stress in sorghum roots
Summary
Aquaporins are integral membrane proteins that form channels that allow water to move from one plant compartment to another They exist in all plants and animals and play important roles in different developmental and physiological processes of living organisms, including stomatal movement, photosynthesis, germination, cell elongation, reproduction, and responses to diverse abiotic stress conditions (Ariani and Gepts, 2015). Plant AQPs were originally classified into four subfamilies: PIPs, TIPs, NIPs, and SIPs (Johanson et al, 2001; Zardoya, 2005). Unlike PIPs, TIPs, NIPs, and SIPs which are present in all land plants, GIPs and HIPs have only been identified in algae and moss, and XIPs only in moss and several dicots (Danielson and Johanson, 2008; Venkatesh et al, 2013; Zhang et al, 2013). Two of the AQP subfamilies, the PIPs, which are usually localized in the plasma membrane, and the TIPs, which are generally localized in the vacuolar membranes, have been investigated intensively in regard to their functions and regulation as related to plant water relations
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