Differential expression of genes in potato tubers after wounding

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Tubers of a common tetraploid species of Solanum tuberosum (Granola) were mechanically wounded by slicing. After 18 hr only small differences were detectable in the pattern of the steady-state protein extracted from wounded versus unwounded tubers. In contrast the protein pattern obtained by in vitro translation of mRNA isolated from wounded and unwounded tubers differed significantly. A cDNA library was established and screened for wound-induced cDNA clones by differential hybridization. Two clones, wun-1 and wun-2, were found that corresponded to genes that were highly expressed in wounded potato tubers but were not expressed in unwounded tubers. The expression of the gene corresponding to wun-1 is detectable 30 min after wounding; the expression of the gene corresponding to wun-2 is detectable 4 hr after wounding. The expression of both genes (hereafter referred to as wun-1 and wun-2) remains constant for up to 24 hr after wounding. Interestingly the RNA corresponding to patatin, a major storage protein of potato tubers, behaves in the opposite way; it decreases dramatically in tubers within 30 min after wounding. The low level of patatin mRNA observed in unwounded roots and stems also disappears after wounding. Run-off transcription experiments, performed with isolated nuclei, indicate that the activation of the wound-induced genes as well as the inhibition of the patatin gene are controlled at the transcriptional level.