ACCUMULATION OF DEFENSE-RELATED TRANSCRIPTS AND CLONING OF A CHITINASE MESSENGER-RNA FROM PEA LEAVES (PISUM-SATIVUM L) INOCULATED WITH ASCOCHYTA-PISI LIB

The race specific resistance of pea to Ascochyta pisi Lib. was shown t o be exhibited as a hypersensitive response associated with the produc tion of polyphenolic substances in epidermal and mesophyll cells. The levels of transcripts representing a pathogenesis-related (PR) protein (chitinase) and an enzyme of phytoalexin biosynthesis (chalcone synth ase) were shown to accumulate more rapidly during the hypersensitive r esponse than during lesion development in the compatible interaction. A full-length (1143 bp) cDNA sequence of a pea chitinase (EC 3.2.1.14) (coding for an approx. 34 500 Da protein) was deduced by combining th e overlapping sequences of three clones obtained following PCR amplifi cation of cDNA prepared from mRNA isolated 24 h after inoculation of p ea leaves with Ascochyta pisi. The combined sequences were identified as a class I chitinase corresponding to the basic A1-chitinase enzyme previously isolated from pea leaves (Vad et al., Planta, 184 (1991) 24 -29). Like class III and IV chitinases, the pea sequence differs from other class I chitinases in the absence of a hydrophobic C-terminal do main.