Isolation and characterization of five ozone-inductible cDNA clones from Atriplax canescens (saltbush)

Abstract

Prolonged exposure of plants to ozone inhibits growth and development and produces visible signs of damage. Within a few hours of exposure, certain biochemical alterations have been observed with the induction of several stress-related proteins. accumulation of several polya RNAS. CDNA clones derived from five different polya RNAs which accumulate in ozone-stressed shrub leaves were isolated by differential screening methods. Alteration in gene expression which occurs with ozone, sulfur dioxide and water deficit were examined, and those cDNAs were sequenced. Clone 012-1, hybridized with three RNA species, is initially induced in response to both ozone and water deficit stress, but is repressed to prolonged ozone and sulfur dioxide exposure. Clone 012-1 has strong homology with small subunit RRNA. Northern blots suggest that transcripts hybridized to 012-1 are a naked species (about 1.45 kb) and are subfragments (1.0 and 0.45 kb) of 1.4 kb species. 0112A-3 showed an increase in response to two pollutants, but not to water deficit. 0112A-3 encodes a polypeptide which has homology with wound-inducible protein inhibitors. MRNA species corresponding to 018-3 are transiently induced in response to sulfur dioxide and water deficit stress, and are late-induced by ozone stress. The 018-3 protein is Ozone fumigation to Atriplex canescens (saltbush) caused the homologous to thiol proteases. Clone OID2-2 and OIS14-3 show similar patterns in gene expression Transcript levels of the two genes rise rapidly and remain at a high level by seven days after ozone fumigation, and rise steadily in response to water deficit and sulfur dioxide stress. The deduced amino acids of both clones are glycine-rich proteins, and they have repeated motifs, (G-G-G-Y-G-H)n, and putative cell wall-targeting signal peptides. Northern analyses indicate that plant cells respond to ozone stress by increasing transcription of several genes. Furthermore, the expression of ozone-inducible genes varies with respect to the time course of induction and different stresses such as water-deficit and sulfur dioxide stress. The encoded proteins suggest that: first, ozone stress may generate wounding damage to increase the expression of the proteinase inhibitor (0112A-3) and the protease (018-3); second, ozone stress may change the cell wall components by increasing the amount of glycine-rich proteins (OID2-2 and OIS14-3); and third, ozone stress may change the cell wall structure with tyrosine-mediated cross-linking, which may use oxyradical-scavenging effects to relieve cellular stress.