Phytophthora infestans produces small phospholipase D-like proteins that elicit plant cell death and promote virulence

Successful invasion of host tissue by biotrophic plant pathogens is dependent on modifications of the host plasma membrane to facilitate two-way transfer of proteins and other compounds. Haustorium formation and establishment of extrahaustorial membranes is likely dependent on a variety of enzymes that modify membranes in a coordinated fashion. Phospholipases, enzymes that hydrolyze phospholipids, have been implicated as virulence factors in several pathogens. The oomycete Phytophthora infestans that causes late blight of potato, is a biotrophic pathogen that possesses different classes of hospholipase D (PLD) proteins including small PLD-like proteins with and without signal peptide (sPLD-likes and PLD-likes, respectively). Here we studied the role of sPLD-like-1, sPLD-like-12 and PLD-like-1 in the infection process. The three encoding genes are expressed in expanding lesions on potato leaves and during growth in vitro with the highest expression levels in germinating cysts. When expressed in planta in the presence of the silencing suppressor P19, all three (s)PLD-likes elicited local cell death, a response that was visible at the microscopic level and was strongly boosted by the presence of calcium. Moreover, inoculation of leaves expressing the (s)PLD-like genes resulted in
increased lesion growth and more sporangia. However, when the PLD catalytic motifs (HDK) were mutated there was neither cell death elicitation nor increased lesion growth thus pointing to the necessity for enzymatic PLD activity in these processes. These results suggest that the P. infestans (s)PLD-likes are catalytically active and function by executing membrane modifications to support growth of this pathogen in the host.