Understanding Aquaporin Transport System in Eelgrass (Zostera marina L.), an Aquatic Plant Species

Abstract

Aquaporins (AQPs) are a class of integral membrane proteins involved in the transport of water and many other small solutes. The AQPs have been extensively studied in many land species obtaining water and nutrients from the soil, but their distribution and evolution have never been investigated in aquatic plant species, where solute assimilation is mostly through the leaves. In this regard, identification of AQPs in the genome of Zostera marina L. (eelgrass), an aquatic ecological model species could reveal important differences underlying solute uptake between land and aquatic species. In the present study, genome-wide analysis led to the identification of 25 AQPs belonging to four subfamilies, plasma membrane intrinsic proteins (PIPs), tonoplast intrinsic proteins (TIPs), nodulin 26-like intrinsic proteins (NIPs), small basic intrinsic proteins (SIPs) in eelgrass. As in other monocots, the XIP subfamily was found to be absent from the eelgrass genome. Further classification of subfamilies revealed a unique distribution pattern, namely the loss of the NIP2 (NIP-III) subgroup, which is known for silicon (Si) transport activity and ubiquitously present in monocot species. This finding has great importance, since the eelgrass population stability in natural niche is reported to be associated with Si concentrations in water. In addition, analysis of available RNA-seq data showed evidence of expression in 24 out of the 25 AQPs across four different tissues such as root, vegetative tissue, male flower and female flower. In contrast to land plants, higher expression of PIPs was observed in shoot compared to root tissues. This is likely explained by the unique plant architecture of eelgrass where most of the nutrients and water are absorbed by shoot rather than root tissues. Similarly, higher expression of the TIP1 and TIP5 families was observed specifically in male flowers suggesting a role in pollen maturation. This genome-wide analysis of AQP distribution, evolution and expression dynamics can find relevance in understanding the adaptation of aquatic and land species to their respective environments.

Role of Silicon in Mitigation of Heavy Metal Stresses in Crop Plants

“…Recently, Ma et al [68] have shown that Si supply under Cd stress in rice upregulated the expression of OsLsi1 (encoding for Si transport NIP-III (Nodulin 26-like intrinsic proteins-III) Aquaporin) and downregulated the expression of Nramp5 , a gene involved in the Cd transport. However, many plant species particularly belonging to family brassicaceae [69], solanaceae [70], and Linaceae [71] does not carry any Si-transporter (NIP-III Aquaporin) and are known as poor Si accumulators. However, several reports suggesting Si derived benefits in such species make it more difficult to understand the molecular consequences [72,73].…”

Identification and characterization of aquaporin genes in Arachis duranensis and Arachis ipaensis genomes, the diploid progenitors of peanut

“…Variation in the number of AQP subfamilies specific to different plant species has been reported. Among the five subfamilies, XIPs are absent entirely from monocots and dicots like Brassicaceae [ 9 – 11 ]. In primitive land plants, two additional unique classes of AQPs, GlpF-like intrinsic protein (GIPs) and hybrid intrinsic proteins (HIPs) have been described and are presumed to have been lost in the course of evolution [ 12 ].…”

Evolutionary Understanding of Aquaporin Transport System in the Basal Eudicot Model Species Aquilegia coerulea

“…Among the seed plants, variation was observed in the distribution of five subfamilies. The entire monocot clade, as well as some dicot families such as the Brassicaceae, have lost the entire XIPs lineage [ 1 , 15 , 50 ]. The absence of the XIPs in rice and Arabidopsis, the two extensively studied model plants, limits the efforts to characterize the functions of XIPs when compared to other subfamilies.…”