Molecular markers for UV-B stress in plants: alteration of the expression of four classes of genes in Pisum sativum and the formation of high molecular mass RNA adducts

Sixteen ultraviolet-B radiation-regulated pea genes were identified. Functi onally, the corresponding proteins were divided into four groups. (i) Chlor oplast-localized proteins. Genes for these proteins were down-regulated, un derlining the deleterious effects of UV-B on this; organelle. A novel down- regulated photosystem I light-harvesting chlorophyll a/b-binding protein ge ne (PsLhcA4), was cloned and sequenced. (ii) Protein turnover enzymes. Leve ls of mature mRNAs for the PU1 and PsUBC4 genes, encoding proteins of the u biquitin protein degradation pathway, were up- and down-regulated, respecti vely, implying alteration of plant cell protein content by changes in both gene expression and protein degradation. (iii) Proteins involved in intrace llular signalling. Expression of genes for small GTPases, rab and rho homol ogues, were altered. (iv) Phenylpropanoid or flavonoid biosynthesis. Expres sion of three genes encoding enzymes in these pathways were up-regulated an d one of them, the novel PsC450R1, was cloned and sequenced. Moreover, unex pected high molecular mass psbA RNA adducts were found to appear after W-B exposure. In addition, a large increase in corresponding high molecular mas s adducts were also found for PsLhcA4, and PsUBC4 mRNA and 23S rRNA. These RNA species do not contain protein and probably appear due to cross-linking of two or more RNA molecules, or are the result of W-B-induced failure of transcription termination. (C) 1999 Elsevier Science B.V. All rights reserv ed.