Genome-wide identification of candidate aquaporins involved in water accumulation of pomegranate outer seed coat

Abstract

Aquaporins (AQPs) are a class of highly conserved integral membrane proteins that facilitate the uptake and transport of water and other small molecules across cell membranes. However, little is known about AQP genes in pomegranate (Punica granatum L.) and their potential role in water accumulation of the outer seed coat. We identified 38 PgrAQP genes in the pomegranate genome and divided them into five subfamilies based on a comparative analysis. Purifying selection played a role in the evolution of PgrAQP genes and a whole-genome duplication event in Myrtales may have contributed to the expansion of PgrTIP, PgrSIP, and PgrXIP genes. Transcriptome data analysis revealed that the PgrAQP genes exhibited different tissue-specific expression patterns. Among them, the transcript abundance of PgrPIPs were significantly higher than that of other subfamilies. The mRNA transcription levels of PgrPIP1.3, PgrPIP2.8, and PgrSIP1.2 showed a significant linear relationship with water accumulation in seed coats, indicating that PgrPIP1.3/PgrPIP2.8 located in the plasma membrane and PgrSIP1.2 proteins located on the tonoplast may be involved in water accumulation and contribute to the cell expansion of the outer seed coat, which then develops into juicy edible flesh. Overall, our results provided not only information on the characteristics and evolution of PgrAQPs, but also insights on the genetic improvement of outer seed coats.

Pearl Millet Aquaporin Gene PgPIP2;6 Improves Abiotic Stress Tolerance in Transgenic Tobacco

“…They are 23–31 kDa proteins having several specific characteristic features, including transmembrane helices (TM) linked by five inter-helical loops (LA-LE) and conserved dual aspargine-proline-alanine (NPA) motifs ( Maurel et al, 2008 ). A number of AQPs have been identified in diverse plant species, including 35 in Arabidopsis ( Johanson et al, 2001 ), 43 in maize ( Chaumont et al, 2001 ), 34 in rice ( Sakurai et al, 2005 ), 58 in Populus ( Gupta and Sankararamakrishnan, 2009 ), 72 in soybean ( Zhang et al, 2013 ), 41 in Sorghum ( Reddy et al, 2015a ), 57 in Brassica rapa ( Sonah et al, 2017 ), 28 in Beta vulgaris ( Kong et al, 2017 ), 65 in wheat ( Madrid-Espinoza et al, 2018 ), 41 in Setaria italica ( Singh et al, 2019 ), 39 in cucumber ( Zhu et al, 2019 ), 76 in tobacco ( De Rosa et al, 2020 ), and 38 in pomegranate ( Liu et al, 2021 ). Plant AQPs show a high degree of gene multiplicity and assembled as tetramers that are typically divided into seven subfamilies, including plasma membrane intrinsic proteins (PIPs), tonoplast intrinsic proteins (TIPs), nodulin-26-like intrinsic proteins (NIPs), and small basic intrinsic proteins (SIPs) that have been identified in both primitive and higher plants ( Anderberg et al, 2012 ).…”

Genome-Wide Identification and Expression Pattern Profiling of the Aquaporin Gene Family in Papaya (Carica papaya L.)

“…Increasingly available plant genomes have enabled the identification and characterization of the AQPs in many plant species, laying a foundation for functional studies. For instance, 35 AQPs were found in A. thaliana [8], 33 in rice [14], 46 in Medicago [11], 39 in cucumber [9], 38 in pomegranate [50], 42 in apple [51], 33 in pineapple [52], 47 in banana [53], 27 in passion fruit [43], and 33 in pitaya [54]. The diverse functions of AQPs have been demonstrated, for example, in regulating plant development and growth and responding to abiotic stress, such as drought, cold, and salt resistance.…”

Expression of Exogenous GFP-CesA6 in Tobacco Enhances Cell Wall Biosynthesis and Biomass Production

“…Moreover, in F 3 1 leaves, we also observed the overexpression of PIP1 and PIP2 ; these genes code for two aquaporin isoforms assembling in heterotrimers at the plasma membrane and able to mediate significant transmembrane water fluxes [ 71 ]. PIP1 and PIP2 were reported to be involved in the expansion of rose petals [ 72 ] and pomegranate flowers [ 73 ], so that the overexpression of these two PIPs in F 3 1 line can be considered a further indication on the effect of GFP - CesA6 expression on the expansion growth.…”