Temporal and genotypic variation of wound-induced gene expression in bark of Populus tremuloides and P-grandidentata

In two related experiments, total RNA was extracted from wounded and unwounded bark of young aspen ramets for Northern and dot blot analyses. Wound-inducible genes isolated from other plant species were hybridized to blots, and mRNA levels were estimated. Analyses of variance (ANOVA) were used to examine the significance of experimental factors (wounding, time after wounding, and genotype) affecting variation in mRNA levels. The first experiment examined the timing (0.5-96 h after wounding) of expression of wound-inducible genes in bark tissue of a single Populus tremuloides Michx, genotype. Wounding and variation among RNA samples significantly (p < 0.05) affected mRNA levels of two chitinases (win6, win8) and phenylalanine ammonia-lyase (PAL). The second experiment examined interclonal variation of wound-induced win6 and PAL expression in aspen bark. Ramets of four P. tremuloides and one Populus grandidentata Michx. genotypes were wounded and bark was collected 4, 8, or 12 h later Genotype, wounding, and time after wounding all significantly affected win6 and PAL mRNA levels, with levels increasing as a result of wounding.