Temporal and spatial patterns of GAPDHc mRNA accumulation during an incompatible potato-Phytophthora infestans interaction. Comparison with a compatible interaction

Most inducible defense responses of plants to pathogens are the result of t ranscriptional activation of specific genes. The cytosolic isoform of the g lycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDHc, EC 1.2.1 .12) increases under environmental constraints, including biological stress . This work was directed to investigate the temporal and spatial distributi on of GAPDHc mRNA during an incompatible potato (Solanum tuberosum L. cv, P ampeana)-Phytophthora infestans interaction. GAPDHc mRNA accumulated earlie r during an incompatible interaction (24 h upon infection) than during a co mpatible one (48 h) and remained over basal levels until late stages of inf ection (96 h). This different pattern for temporal accumulation in,whole po tato plants could be part of the rapid defense responses observed when plan ts are resistant to infection. During the incompatible interaction, the mos t important GAPDHc mRNA induction (20-fold increase) relative to basal leve ls.;lt 12 h post-inoculation, occurred at the site of infection, whereas a 13-fold increase occurred in the uninfected surrounding tissue of inoculate d points. At later stages (24 h), the highest induction was observed in uni noculated leaflets (15-fold) whereas the le, els in the inoculated leaflets (both the inoculated points and the! surrounding areas) remained above the levels present at time zero of infection (8- and Ii-fold, respectively!), These results suggest that the signal responsible for GAPDHc mRNA accumulat ion in plants during infection is first activated in infected tissues, but is then transmitted to uninfected parts, Furthermore, biochemical responses in plants upon pathogen attack include components of primary metabolism,, and this could be involved in physiological host adaptations against pathog en spreading.