Pectate lyase of Colletotrichum gloeosporioides attacking avocado fruits: cDNA cloning and involvement in pathogenicity

Polyclonal antibodies were used to study the secretion of a pectate lyase: PLj during infection of avocado fruits by Colletotrichum gloeosporioides. Pectate lyase was detected in decayed fruit tissue 5 days after fruit inoculation, concomitantly with the decrease of the preformed antifungal 1-acetoxy-2-hydroxy-4-oxo-12,15-heneicosa diene to subfungitoxic concentrations. A higher amount of the enzyme was detected in the leading edge of the decayed lesion than in the already decayed tissue. As a first stage to determine the relation between PLs form C. gloeosporioides attacking avocado and PLs from Colletotrichum strains attacking other fruits, a cDNA encoding PL of C. gloeosporioides was cloned and sequenced. The cloned DNA showed high homology to known pels from fungi, bacteria and plants. The pel gene of C. gloeosporioides hybridized to single genomic restriction fragments from C. gloeosporioides isolated from mango and papaya fruits and Colletotrichum musae from banana fruit. Western blot analysis of culture fluids from these pathogens revealed one band of 28 41 kDa that specifically cross-reacted with antibodies raised against the pectate lyase from C. gloeosporioides isolated from avocado. Pectate lyase antibodies had no effect on spore germination, germ tube elongation or appressoria formation. However, when conidia were mixed with the antibodies prior to inoculation, symptom development was inhibited on avocado, mango and banana fruits. These results suggest the presence of a similar PL in Colletotrichum strains attacking avocado, mango, papaya and banana. The detection and inhibition of fungal development by PL antibodies suggest the importance of this enzyme during C. gloeosporioides attack in fruits.