A novel stress-inducible antioxidant enzyme identified from the resurrection plant Xerophyta viscosa Baker

Abstract

A cDNA corresponding to 1-Cys peroxiredoxin, an evolutionarily conserved thiol-specific antioxidant enzyme, was isolated from Xerophyta viscosa Baker, a resurrection plant indigenous to Southern Africa and belonging to the family Velloziaceae. The cDNA, designated XvPer1, contains an open reading frame that encodes a polypeptide of 219 residues with a predicted molecular weight of 24.2 kDa. The XvPer1 polypeptide shows significant sequence identity (approx. 70%) to other recently identified plant 1-Cys peroxiredoxins and relatively high levels of sequence similarity (approx. 40%) to non-plant 1-Cys peroxiredoxins. The XvPer1 cDNA contains a putative polyadenylation site. As for all 1-Cys peroxiredoxins identified to date, the amino acid sequence proposed to constitute the active site of the enzyme, PVCTTE, is highly conserved in XvPer1. It also contains a putative bipartite nuclear localization signal. Southern blot analysis revealed that there is a single copy of XvPer1 in the X. viscosa genome. All angiosperm 1-Cys peroxiredoxins described to date are seed-specific and absent in vegetative tissues even under stress conditions; therefore, XvPer1 is unique in that it is expressed in the vegetative tissues of X. viscosa. The XvPer1 transcript was absent in fully hydrated X. viscosa tissue but levels increased in tissues subjected to abiotic stresses such as dehydration, heat (42 degrees C), high light intensity (1,500 micro mol photons m(-2) s(-1)) and when treated with abscisic acid (100 micro M ABA) and sodium chloride (100 mM NaCl). Western blot analyses correlated with the patterns of expression of XvPer1 transcripts under different stress conditions. Immunofluorescence analyses revealed that XvPer1 is localized in the nucleus of dehydrated X. viscosa leaf cells. These results suggest that XvPer1 is a stress-inducible gene, which may function to protect nucleic acids within the nucleus against oxidative injury.

Seed 1-Cysteine Peroxiredoxin Antioxidants Are Not Involved in Dormancy, But Contribute to Inhibition of Germination during Stress

“…This gene was up-regulated when the plant was dehydrated and during drought and heat stress, which are known to elevate the ROS production as a result of stomatal closing and reduced CO 2 availability. In accordance with a putative bipartite nuclear localization signal (NLS) found in plant 1-Cys Prxs, XvPER1 was localized to the nucleus (Mowla et al, 2002). Barley PER1 has also been localized to the nucleus of cells of the developing embryo and aleurone layer, although a weak signal was also detected in the cytoplasm.…”

“…Recently, Mowla et al (2002) have shown that expression of XvPer1 from the resurrection plant X. viscosa was induced upon dehydration of vegetative tissue, a condition known to induce ROS production. Tr155, a homolog from Tortula ruralis is expressed in the gametophyte in response to desiccation and rehydration (Wood et al, 2000).…”

“…Plant 1-Cys Prxs have been suggested to contain a bipartite NLS at the 3Ј end (Stacy et al, 1999;Mowla et al, 2002). Analysis of the AtPER1 sequence using PSORT (http://psort.nibb.ac.jp/) and PredictNLS (http://cubic.bioc.columbia.edu/predictNLS/) predicted cytoplasmic localization to be most likely for AtPER1.…”

“…In imbibed barley embryo and aleurone cells, labeling of similar strength was found in the cytoplasm and in the nucleus (Stacy et al, 1999). A role in protection of nucleic acids against ROS has been suggested (Stacy et al, 1999;Mowla et al, 2002).…”

“…Recently, a new member of the 1-Cys Prx group, XvPer1, was isolated from the resurrection plant Xerophyta viscosa (Mowla et al, 2002). This gene was up-regulated when the plant was dehydrated and during drought and heat stress, which are known to elevate the ROS production as a result of stomatal closing and reduced CO 2 availability.…”