Low level of pathogenesis-related protein 1 mRNA expression in 15-day-old Arabidopsis cer6-2 and cer2 eceriferum mutants

RNA from the aerial parts of 15-day-old eceriferum cer6-2 mutant and control plants were used in microarray experiments to screen for differentially expressed genes. Among those which were down-regulated in the mutant, several were known to be involved in various plant defense mechanisms. The most remarkable difference was measured for the transcripts encoding the pathogenesis-related protein1 (PR-1), which is a marker of the systemic acquired resistance (SAR) pathway, with a 100-fold decrease in the cer6-2 mutant. Further, Q-PCR experiments showed that the PR-1 transcript levels were low in two other eceriferum mutants, representing 1/200th and 1/25th of the normal values in the aerial part of 15-day-old cer2 and cer1-1 mutants, respectively. Interestingly, PR-1 mRNA levels were closed to the normal values in the cer3-1 and cer6-2R mutant, the latter being a plant where the synthesis of the very-long chain fatty acids, which is deficient in the cer6-2 plants, is partially restored. Altogether, these results strongly suggested that the amount of PR1-mRNA was not directly correlated to the amount of epicuticular wax on the leaves, but was rather correlated to the presence or absence of some particular lipid-constituents in the epicuticular wax layer.