An Expression Analysis of a Gene Family Encoding Plasma Membrane Aquaporins in Response to Abiotic Stresses in Arabidopsis Thaliana

Abstract

Aquaporin belongs to a highly conserved group of membrane proteins called major intrinsic proteins that facilitate water transport across biological membranes. The genome of Arabidopsis encodes 35 aquaporin genes with 13 homologs in the plasma membrane intrinsic protein (PIP) subgroup. However, the function of each individual aquaporin isoform and the integrated function of plant aquaporins under various physiological conditions remain unclear. As a step toward understanding the aquaporin function in plants under various environmental stimuli, the expressions of a gene family encoding 13 PIPs in Arabidopsis thaliana under various abiotic stress conditions including drought, cold, and high salinity, or abscisic acid (ABA) treatment were investigated by a quantitative real-time reverse transcription-PCR analysis. Several PIP genes were predominantly expressed either in the roots or in the flowers. The expressions of both the highly expressed aquaporins including PIP1;1, PIP1;2, and PIP2;7 and the weakly expressed aquaporins such as PIP1;4, PIP2;1, PIP2;4, and PIP2;5 were modulated by external stimuli. The analyses of our data revealed that only the PIP2;5 was up-regulated by cold treatment, and most of the PIP genes were down-regulated by cold stress. Marked up- or down-regulation in PIP expression was observed by drought stress, whereas PIP genes were less-severely modulated by high salinity. The responsiveness of each aquaporin to ABA were different, implying that the regulation of aquaporin expression involves both ABA-dependent and ABA-independent signaling pathways. Together, our comprehensive expression profile of the 13 members of the PIP gene family provides novel basis to allocate the stress-related biological function to each PIP gene.

Expression and functional analysis of the rice plasma-membrane intrinsic protein gene family

“…Similar to the Arabidopsis AtPIP gene family [17], the rice OsPIP familly exhibits significant differences in mRNA abundance among its members (Figure 2). The overall transcript level of OsPIP2-4 was the highest, accounting for about 75% of the total OsPIP transcripts in the seedlings at two weeks after germination.…”

“…For a negative control, the PCR was performed without cDNA templates. The absolute and relative transcript copy number of OsPIP genes in each treated sample was calculated following the method described by Jang et al [17], except that a rice actin gene (OsACT1) was used to calculate the correction factor instead of the Arabidopsis actin gene.…”

“…However, when the concentration of NaCl was increased to 150 mM, the growth of both the transgenic and control lines were strongly inhibited ( Figure 6B and 6C). Furthermore, when the transgenic lines were exposed to 200 mM of mannitol which was used to mimic drought stress in Arabidopsis [17], the growth of the main roots was not affected compared to the control line ( Figure 6B and 6C). Interestingly, similar phenotypes had been observed for the OsPIP2-2 over-expression transgenic lines ( Figure 6D).…”

“…The expression patterns of aquaporin genes in response to salt, drought, cold, submergence, light, and phytohormones have also been characterized in various plants [16][17][18][19][20][21][22][23][24]. Some aquaporins are tissue-specific, such as g-MIP in shoots of rice [21], g-TIP in seeds of Brassica napus [16] and ZmTIP2-3 in roots of maize [25].…”

“…There were thirteen PIP genes among the identified thirty and thirty-one aquaporin genes in Arabidopsis and maize, respectively [13,26]. The function and expression patterns of the PIP gene family have been intensively studied in Arabidopsis, Brassicca, and maize, especially in response to abiotic stress [7,17,18,[26][27][28][29].…”