Abstract
Aquaporins (AQPs) are of vital importance in the cellular transport system of all living organisms. In this study, genome-wide identification, distribution, and characterization of AQPs were determined in Arabidopsis lyrata, Capsella grandiflora, C. rubella, Eutrema salsugineum, Brassica rapa, B. oleracea, and B. napus (canola). Classification and phylogeny of AQPs revealed the loss of XIPs and NIP-IIIs in all species. Characterization of distinctive AQP features showed a high level of conservation in spacing between NPA-domains, and selectivity filters. Interestingly, TIP3s were found to be highly expressed in developing seeds, suggesting their role in seed desiccation. Analysis of available RNA-seq data obtained under biotic and abiotic stresses led to the identification of AQPs involved in stress tolerance mechanisms in canola. In addition, analysis of the effect of ploidy level, and resulting gene dose effect performed with the different combinations of Brassica A and C genomes revealed that more than 70% of AQPs expression were dose-independent, thereby supporting their role in stress alleviation. This first in-depth characterization of Brassicaceae AQPs highlights transport mechanisms and related physiological processes that could be exploited in breeding programs of stress-tolerant cultivars.
Highlights
Aquaporins (AQPs) are integral membrane proteins that facilitate the transport of water and many other small molecules like urea, boric acid, silicic acid, ammonia, and carbon dioxide[1,2,3]
Unique patterns of subcellular localization have been observed in proteins within each AQP sub-family; for instance, plasma membrane intrinsic proteins (PIPs) are mostly localized to the plasma membrane, tonoplast intrinsic proteins (TIPs) to the tonoplast, NOD26-like intrinsic proteins (NIPs) to the plasma membrane or the endoplasmic reticulum, small basic intrinsic proteins (SIPs) to the endoplasmic reticulum, and XIPs mostly to the plasma membrane[4, 5]
As previously described in Arabidopsis, PIPs represented the highest number of AQPs followed by TIPs, NIPs, and SIPs, with the exception for C. grandiflora that has nine AQPs each in TIP and NIP categories
Summary
Aquaporins (AQPs) are integral membrane proteins that facilitate the transport of water and many other small molecules like urea, boric acid, silicic acid, ammonia, and carbon dioxide[1,2,3]. 35 AQPs in Arabidopsis, 34 in rice, 55 in poplar and 72 in soybean have been reported compared to only 13 in the human genome[12, 14] This higher and differential number of AQPs in plants is likely the result of gene duplication and higher ploidy levels in plants[12, 15]. Shi, et al.[17] analyzed gene expression dose effect using resynthesized Arabidopsis tetraploids harboring varied copies of chromosomes from model plant species Arabidopsis thaliana and Arabidopsis arenosa genomes. They observed that the genes mostly involved in cell cycle, photosynthesis, and metabolism are dosage-dependent, whereas genes involved in biotic and abiotic stress tolerance mechanisms are dosage-independent.
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