Genome-Wide Identification and Characterization of the Aquaporin Gene Family and Transcriptional Responses to Boron Deficiency in Brassica napus

Abstract

Aquaporins (AQPs) are an abundant protein family and play important roles to facilitate small neutral molecule transport across membranes. Oilseed rape (Brassica napus L.) is an important oil crop in China and elsewhere in the world, and is very sensitive to low boron (B) stress. Several AQP family genes have been reported to be involved in B transport across plasma membranes in plants. In this study, a total of 121 full-length AQPs were identified and characterized in B. napus (AC genome), and could be classified into four sub-families, including 43 PIPs (plasma membrane intrinsic proteins), 35 TIPs (tonoplast intrinsic proteins), 32 NIPs (NOD26-like intrinsic proteins), and 11 SIPs (small basic intrinsic proteins). The gene characteristics of BnaAQPs were similar to those of BraAQPs (A genome) and BolAQPs (C genome) including the composition of each sub-family, gene structure, and substrate selectivity filters. The BnaNIP was the most complex AQP sub-family, reflecting the composition of substrate selectivity filter structures which affect the permeation of solution molecules. In this study, the seedlings of both B-efficient (QY10) and B-inefficient (W10) cultivars were treated with two boron (B) levels: deficient (0.25 μM B) and sufficient (25 μM B). The transcription of AQP genes in root (R), juvenile leaf (JL), and old leaf (OL) tissues of both cultivars was investigated under B deficient and sufficient conditions. Transcription of most BnaPIPs and BnaTIPs was significantly increased compared with other BnaAQPs in all the three tissues, especially in the roots, of both B-efficient and B-inefficient cultivars under both B conditions. With B deprivation, the expression of the majority of the BnaPIPs and BnaTIPs was down-regulated in the roots. However, the BnaNIPs were up-regulated. In addition, the BnaCnn_random.PIP1;4b, BnaPIP2;4s, BnaC04.TIP4;1a, BnaAnn_random.TIP1;1b, and BnaNIP5;1s (except for BnaA07.NIP5;1c and BnaC06.NIP5;1c) exhibited obvious differences at low B between B-efficient and B-inefficient cultivars. These results will help us to understand boron homeostasis in B. napus.

Boron demanding tissues of Brassica napus express specific sets of functional Nodulin26‐like Intrinsic Proteins and BOR1 transporters

“…For Darmor‐bzh NIP s and BOR s the trivial names given by Yuan et al . () and Chen et al . () were used, while for Zhongshuang11 NIP s and BOR s the locus gene identifier name was used.…”

“…Using this growth set‐up, we determined tissue‐ and B‐dependent expression patterns at ≥ BBCH60 to understand when and where NIPs might play a role in floral B transport fluxes. Thereby, we demonstrated that the previously root‐specific defined BnaA02.NIP6;1a isoform (Yuan et al ., ) is actually highly expressed in the inflorescence (Figure b). Moreover, we demonstrated that BnaC05.NIP3;1b, BnaA05.NIP3;1b and NIP7 isoforms are strongly expressed in various inflorescence tissues, including the rachis and the open‐ and closed flowers.…”

“…Recently, two independent studies reported on the BOR and the aquaporin gene family of Darmor‐bzh , and identified 32 NIPs and 20 BORs, respectively (Yuan et al ., ; Chen et al ., ). We identified one additional full‐length BOR sequence in the Darmor‐bzh genome.…”

“…This indicates that the delivery of B to and its allocation within the flowers is tightly managed by both NIPs and BORs, and further highlights the role of B for the fertility of plants. Comparing our Darmor‐PBY018 expression results with previous studies on QY10 or W10 (Yuan et al ., ; Chen et al ., ), we can conclude that cultivar‐specific B transporter expression characteristics exist. Such a diversity is fundamental for breeding strategies aiming at improving the B efficiency of Brassica crops to face future agricultural challenges.…”

Overexpression of X Intrinsic Protein 1;1 in Nicotiana tabacum and Arabidopsis reduces boron allocation to shoot sink tissues

“…Compared to 13 isoforms in humans (Agre & Kozono, 2003), a relatively large number of isoforms are expressed in plants e.g. 35 MIPs in Arabidopsis thaliana (Johanson et al, 2001), 71 in cotton (Park, Scheffler, Bauer, & Campbell, 2010) and even 121 in Brassica napus (Yuan et al, 2017). In vascular plants, MIPs phylogenetically cluster into four to five distinct subfamilies namely the Plasma membrane Intrinsic Proteins (PIPs), Tonoplast Intrinsic Proteins (TIPs), Small basic Intrinsic Proteins (SIPs), Nodulin26-like Intrinsic Proteins (NIPs) and the X-Intrinsic Proteins (XIPs).…”