Abstract
Aquaporins (AQPs) are a class of integral membrane proteins that facilitate the passive transport of water and other small solutes across biological membranes. Castor bean (Ricinus communis L., Euphobiaceae), an important non-edible oilseed crop, is widely cultivated for industrial, medicinal and cosmetic purposes. Its recently available genome provides an opportunity to analyze specific gene families. In this study, a total of 37 full-length AQP genes were identified from the castor bean genome, which were assigned to five subfamilies, including 10 plasma membrane intrinsic proteins (PIPs), 9 tonoplast intrinsic proteins (TIPs), 8 NOD26-like intrinsic proteins (NIPs), 6 X intrinsic proteins (XIPs) and 4 small basic intrinsic proteins (SIPs) on the basis of sequence similarities. Functional prediction based on the analysis of the aromatic/arginine (ar/R) selectivity filter, Froger’s positions and specificity-determining positions (SDPs) showed a remarkable difference in substrate specificity among subfamilies. Homology analysis supported the expression of all 37 RcAQP genes in at least one of examined tissues, e.g., root, leaf, flower, seed and endosperm. Furthermore, global expression profiles with deep transcriptome sequencing data revealed diverse expression patterns among various tissues. The current study presents the first genome-wide analysis of the AQP gene family in castor bean. Results obtained from this study provide valuable information for future functional analysis and utilization.
Highlights
Aquaporins (AQPs) are a special class of integral membrane proteins that belong to the ancient major intrinsic protein (MIP) superfamily [1,2]
Based on the statistical analysis, Froger et al proposed five conserved amino acid residues for discriminating glycerol-transporting aquaglyceroporins (GLPs) from water-conducting AQPs: GLPs usually feather an aromatic residue at P1, an acidic residue at P2, a basic residue at P3, a proline followed by a nonaromatic residue at P4 and P5, as Y108-D207-K211-P236-L237 observed in the Escherichia coli glycerol facilitator GlpF in contrast to A103-S190-A194-F208-W209 in the pure water channel AqpZ [9]
Plant AQPs are divided into seven main subfamilies, i.e., plasma membrane intrinsic proteins (PIPs), tonoplast intrinsic proteins (TIPs), NOD26-like intrinsic proteins (NIPs), small basic intrinsic proteins (SIPs), uncategorized X intrinsic proteins (XIPs), GlpF-like intrinsic proteins (GIPs) and hybrid intrinsic proteins (HIPs) [16,17,18,19]
Summary
Aquaporins (AQPs) are a special class of integral membrane proteins that belong to the ancient major intrinsic protein (MIP) superfamily [1,2]. Plant AQPs are divided into seven main subfamilies, i.e., plasma membrane intrinsic proteins (PIPs), tonoplast intrinsic proteins (TIPs), NOD26-like intrinsic proteins (NIPs), small basic intrinsic proteins (SIPs), uncategorized X intrinsic proteins (XIPs), GlpF-like intrinsic proteins (GIPs) and hybrid intrinsic proteins (HIPs) [16,17,18,19] The former four subfamilies are widely distributed whereas GIPs and HIPs are only found in algae and moss, and XIPs in moss and several dicots including poplar (Populus trichocarpa) [11,12,13,14,15,16,17,18,19,20]
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