PRIMARY STRUCTURE AND EXPRESSION OF MESSENGER-RNAS ENCODING BASIC CHITINASE AND 1,3-BETA-GLUCANASE IN POTATO

Infection of potato leaves (Solanum tuberosum L. cv. Datura) by the la te blight fungus Phytophthora infestans, or treatment with fungal elic itor leads to a strong increase in chitinase and 1,3-beta-glucanase ac tivities. Both enzymes have been implicated in the plant's defence aga inst potential pathogens. In an effort to characterize the correspondi ng genes, we isolated complementary DNAs encoding the basic forms (cla ss I) of both chitinase and 1,3-beta-glucanase, which are the most abu ndant isoforms in infected leaves. Sequence analysis revealed that at least four genes each are expressed in elicitor-treated leaves. The st ructural features of the potato chitinases include a hydrophobic signa l peptide at the N-terminus, a hevein domain which is characteristic o f class I chitinases, a proline- and glycine-rich linker region which varies among all potato chitinases, a catalytic domain, and a C-termin al extension. The potato 1,3-beta-glucanases also contain a N-terminal hydrophobic signal peptide and a C-terminal extension, the latter com prising a potential glycosylation site. RNA blot hybridization experim ents showed that basic chitinase and 1,3-beta-glucanase are strongly a nd coordinately induced in leaves in response to infection, elicitor t reatment, ethylene treatment, or wounding. In addition to their activa tion by stress, both types of genes are regulated by endogenous factor s in a developmental and organ-specific manner. Appreciable amounts of chitinase and 1,3-beta-glucanase mRNAs were found in old leaves, stem s, and roots, as well as in sepals of healthy, untreated plants, where as tubers, root tips, and all other flower organs (petals, stamen, car pels) contained very low levels of both mRNAs. In young leaves and ste ms, chitinase and 1,3-beta-glucanase were differentially expressed. Wh ile chitinase mRNA was abundant in these parts of the plant, 1,3-beta- glucanase mRNA was absent. DNA blot analysis indicated that in potato, chitinase and 1,3-beta-glucanase are encoded by gene families of cons iderable complexity.