Distinct ultraviolet-signaling pathways in bean leaves. DNA damage is associated with beta-1,3-glucanase gene induction, but not with flavonoid formation.
The enzyme beta-1,3-glucanase (betaGlu) was found to be strongly induced by ultraviolet (UV-B; 280-320 nm) radiation in primary leaves of French bean (Phaseolus vulgaris). This was demonstrated on the level of gene transcription, protein synthesis, and enzyme activity and was due to the expression of bean class I betaGlu (betaGlu I). In contrast to other proteins of the family of pathogenesis-related proteins, the induction of betaGlu I by UV correlated with the formation of photoreversible DNA damage, i.e. pyrimidine dimer formation. In conditions that allowed photorepair of this damage, betaGlu I induction was blocked. Therefore, UV-induced DNA damage seems to constitute a primary signal in the pathway leading to the induction of the betaGlu I gene(s). The induction was a local response because in partly irradiated leaves betaGlu I was selectively found in leaf parts exposed to UV. Although short wavelength UV (lambda < 295 nm) was most efficient in betaGlu I induction, longer wavelength UV (lambda > 295 nm) as present in natural radiation was still effective. In contrast to UV induction of betaGlu I, the induction of flavonoids in bean leaves was optimally triggered by much more moderate fluences from the UV wavelength range no longer effective in betaGlu I induction. UV induction of the flavonoid pathway shows no correlation with DNA damage and thus should be mediated via a different signal transduction pathway.
Kucera
Birgit
B
Institut für Biologie II, Albert-Ludwigs-Universität Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany.
Leubner-Metzger
Gerhard
G
Wellmann
Eckard
E
D001483:Base Sequence; D004249:DNA Damage / Q000235:genetics*; D017931:DNA Primers; D018744:DNA, Plant / Q000528:radiation effects; D004790:Enzyme Induction / Q000528:radiation effects; D005419:Flavonoids / Q000096:biosynthesis*; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant / Q000235:genetics* / Q000528:radiation effects; D043326:Glucan 1,3-beta-Glucosidase / Q000096:biosynthesis / Q000235:genetics* / Q000528:radiation effects; D007700:Kinetics; D027805:Phaseolus / Q000235:genetics / Q000502:physiology / Q000528:radiation effects*; D018515:Plant Leaves / Q000201:enzymology / Q000528:radiation effects; D016133:Polymerase Chain Reaction; D015398:Signal Transduction / Q000528:radiation effects*; D015533:Transcriptional Activation
D017931:DNA Primers; D018744:DNA, Plant; D005419:Flavonoids; D043326:Glucan 1,3-beta-Glucosidase