Structure and expression of the genes encoding proteins resident in large peripheral vesicles of Phytophthora cinnamomi zoospores

Zoospores of Phytophthora spp. contain several characteristic types of peri pheral vesicles. One of these, large peripheral vesicles, has been proposed to act as a nutrient store and in P. cinnamomi has been shown to contain t hree immunologically related high-molecular-weight proteins, designated LPV s. We have used antibodies directed against P. cinnamomi zoospores and cyst s to isolate several cDNA clones which are products of the Lpv genes and en code one or more of the LPV proteins present in large peripheral vesicles. Northern blot analysis demonstrated the presence of three large Lpv transcr ipts (11-14 kb) in RNA isolated from hyphae which had been induced to form sporangia. Coordinate accumulation of the three transcripts occurred after induction of sporangium formation: no transcript was observed in uninduced hyphae and maximum transcript levels of all three transcripts were seen 4-6 h after induction. Genomic Southern blots indicated that P. cinnamomi cont ains three Lpv genes. presumably corresponding to the three transcripts and proteins seen in Northern and Western blots, respectively. Partial genomic clones representing two of the Lpv genes were isolated and characterized b y restriction mapping and partial DNA sequencing. In the regions sequenced, the genes were >99% identical, the high degree of conservation extending a t least 415 bp downstream of their polyadenylation sites. The Lpv coding re gions contained a variable number (approximately 12-18) of highly conserved 534bp repeats, flanked by apparently unique sequences. Variation in the nu mber of repeats in the Lpv genes was responsible for the different sizes of the three transcripts and proteins. Database searches using the Lpv nucleo tide and deduced amino acid sequences failed to detect any similar sequence s. We discuss the molecular events which may have been involved in the evol ution of the Lpv genes and the nature of the products of these genes.