The Eucalyptus Tonoplast Intrinsic Protein (TIP) Gene Subfamily: Genomic Organization, Structural Features, and Expression Profiles.

Marcela I Rodrigues,Juliana P Bravo,Ivan G Maia,Agnes A S Takeda

doi:10.3389/fpls.2016.01810

Marcela I Rodrigues, Juliana P Bravo + Show 2 more

Open Access

https://doi.org/10.3389/fpls.2016.01810

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Abstract

Plant aquaporins are water channels implicated in various physiological processes, including growth, development and adaptation to stress. In this study, the Tonoplast Intrinsic Protein (TIP) gene subfamily of Eucalyptus, an economically important woody species, was investigated and characterized. A genome-wide survey of the Eucalyptus grandis genome revealed the presence of eleven putative TIP genes (referred as EgTIP), which were individually assigned by phylogeny to each of the classical TIP1–5 groups. Homology modeling confirmed the presence of the two highly conserved NPA (Asn-Pro-Ala) motifs in the identified EgTIPs. Residue variations in the corresponding selectivity filters, that might reflect differences in EgTIP substrate specificity, were observed. All EgTIP genes, except EgTIP5.1, were transcribed and the majority of them showed organ/tissue-enriched expression. Inspection of the EgTIP promoters revealed the presence of common cis-regulatory elements implicated in abiotic stress and hormone responses pointing to an involvement of the identified genes in abiotic stress responses. In line with these observations, additional gene expression profiling demonstrated increased expression under polyethylene glycol-imposed osmotic stress. Overall, the results obtained suggest that these novel EgTIPs might be functionally implicated in eucalyptus adaptation to stress.

Highlights

Aquaporins are membrane channels implicated in the transfer of water and small solutes across cell membranes
The exon/intron organization of the mined EgTIP genes was determined using the Eucalyptus gene models annotated in Phytozome and the Gene Structure Display Server2 (GSDS v2.0)
Additional stress-related regulatory elements found in a small number of EgTIP promoters include TC-rich motifs, LTR, HSE and C-repeat/DRE (Table 2). These findings indicate that the EgTIP genes are regulated by phytohormones such as abscisic acid (ABA) and methyl jasmonate (MeJA) and differentially responsive to a set of abiotic stimuli

Summary

Introduction

Aquaporins are membrane channels implicated in the transfer of water and small solutes across cell membranes (reviewed in Maurel et al, 2015). Members of the Tonoplast Intrinsic Protein (TIP) subfamily are generally targeted to the vacuolar membrane and known to facilitate water transport across this subcellular compartment. Parallel to their role as water channels, TIP isoforms can translocate glycerol, hydrogen peroxide (H2O2) (reviewed in Maeshima, 2001) and urea (Liu et al, 2003), and enhance vacuolar membrane permeability to ammonia (Loqué et al, 2005; Kirscht et al, 2016). Specificity of substrate transport is mainly determined by four amino acid (aa) residues present at specific positions of the so-called aromatic/arginine (ar/R) selectivity filter, which acts as a size-exclusion barrier (Sui et al, 2001; Wu et al, 2009).

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