A vacuolar antiporter is differentially regulated in leaves and roots of the halophytic wild rice Porteresia coarctata (Roxb.) Tateoka

Abstract

Vacuolar NHX-type antiporters play a role in Na(+)/K(+) uptake that contributes to growth, nutrition and development. Under salt/osmotic stress they mediate the vacuolar compartmentalization of K(+)/Na(+), thereby preventing toxic Na(+)K(+) ratios in the cytosol. Porteresia coarctata (Roxb.) Tateoka, a mangrove associate, is a distant wild relative of cultivated rice and is saline as well as submergence tolerant. A vacuolar NHX homolog isolated from a P. coarctata cDNA library (PcNHX1) shows 96 % identity (nucleotide level) to OsNHX1. Diurnal PcNHX1 expression in leaves was found to be largely unaltered, though damped by salinity. PcNHX1 promoter directed GUS expression is phloem-specific in leaves, stem and roots of transgenic plants in the absence of stress. Under NaCl stress, GUS expression was also seen in the epidermal and sub-epidermal layers (mesophyll, guard cells and trichomes) of leaves, root tip. The salinity in the rhizosphere of P. coarctata varies considerably due to diurnal/semi-diurnal tidal inundation. The diurnal expression of PcNHX1 in leaves and salinity induced expression in roots may have evolved in response to dynamic changes in salinity of in the P. coarctata rhizosphere. Despite high sequence conservation between OsNHX1 and PcNHX1, the distinctive expression pattern of PcNHX1 exemplifies how variation in expression is fine tuned to suit the halophytic growth habitat of a plant.

Back to the Wild: On a Quest for Donors Toward Salinity Tolerant Rice

“…Several genes have been sequenced by PCR-based cloning, but only 498 ESTs are available in the NCBI database to date (Chowrasia et al, 2019). The transcription of OcNHX1 was found to be regulated during the day in seawater and was also rapidly induced by salinity treatment to sequester Na + into vacuoles (Kizhakkedath et al, 2015). Some O. coarctata proteins involved in ROS detoxification, photorespiration, cell wall biosynthesis, are highly upregulated under salinity stress in leaves (Sengupta and Majumder, 2009).…”

A walk on the wild side: Oryza species as source for rice abiotic stress tolerance

“…A tonoplast-localized transporter from the NHX family of O. coarctata was recently cloned. PcNHX1 transcription is regulated during the day, presumably reflecting the circadian variation in tide experienced by the plant, and is also rapidly induced by NaCl treatment, compartmentalizing Na + into vacuoles (Kizhakkedath et al , 2015). Thus, O. coarctata is adapted to high salinity environments by using multiple mechanisms to cope with salt stress, including decreased root-to-shoot translocation and increased compartmentalization in the vacuole and secretion in salt hairs.…”

Distinct Evolutionary Origins of Intron Retention Splicing Events in NHX1 Antiporter Transcripts Relate to Sequence Specific Distinctions in Oryza Species

“…NHX1 sequences were retrieved from Ensembl Plants 1 using O. coarctata NHX1 genomic sequence as query (Accession No. JQ796375.1; Kizhakkedath et al, 2015) and searched against Oryza sativa japonica (IRGSP-1.0; Supplementary Table S1). The Na + /H + exchanger domain was identified in corresponding NHX1 protein sequences using HMMER v 2.28.0 2 , and domain boundaries were manually curated based on multiple sequence alignment (MSA) generated using CLUSTALW2 3 .…”

“…RT-PCR analysis of salinity-treated O. coarctata leaf tissues (150 mM NaCl) confirmed that the IR splicing event observed for OsNHX1 (13th intron) is also conserved in O. coarctata (OcNHX1i13; 680 bp); this was further confirmed by RT-PCR amplification of fragments of varying sizes using primers flanking the 13th intron (209, 680, 593, and 152 bp; Figures 4A-E). The 680 bp fragment showed 100% identity with the OcNHX1 genomic sequence: Accession no: JQ796375.1 (Kizhakkedath et al, 2015; Figure 4F). The 3 RACE PCR OcNHX1i13 product shows complete retention of the 13th intron and 14th exon (Supplementary Figure S7).…”

“…The following splice variants were examined: correctly spliced transcript (cDNA), 13th intron retaining transcript (NHXi13), the 5 UTR intron retaining NHX1 transcript (R-NHX1) and the 5 UTR intron splicing NHX1 transcript (Sp-NHX1). (A) For the correctly spliced NHX1 transcript 12th exon forward primer (RT-F2) and 13th-12th exon reverse (RT-R2) primers were used (Kizhakkedath et al, 2015). For the 13th intron retention transcript i13F (12th exon-13th intron junction) and i13R (13th intron) primers were used.…”