Plant-parasitic
cyst nematodes penetrate plant roots and transform cells near the vasculature into specialized feeding sites called syncytia. Syncytia form by incorporating neighboring cells into a single fused cell by cell wall dissolution. This process is initiated via injection of esophageal gland cell effector
proteins from the nematode stylet into the host cell. Once inside the cell, these
proteins may interact with host
proteins that regulate the
phytohormone auxin, as cellular concentrations of
auxin increase in developing syncytia. Soybean
cyst nematode (Heterodera glycines) Hg19C07 is a novel effector
protein expressed specifically in the dorsal gland cell during nematode parasitism. Here, we describe its ortholog in the beet
cyst nematode (Heterodera schachtii), Hs19C07. We demonstrate that Hs19C07 interacts with the Arabidopsis (Arabidopsis thaliana)
auxin influx transporter LAX3. LAX3 is expressed in cells overlying lateral root primordia, providing
auxin signaling that triggers the expression of cell wall-modifying
enzymes, allowing lateral roots to emerge. We found that LAX3 and
polygalacturonase, a LAX3-induced cell wall-modifying
enzyme, are expressed in the developing syncytium and in cells to be incorporated into the syncytium. We observed no decrease in H. schachtii infectivity in aux1 and lax3 single mutants. However, a decrease was observed in both the aux1lax3 double mutant and the aux1lax1lax2lax3 quadruple mutant. In addition, ectopic expression of 19C07 was found to speed up lateral root emergence. We propose that Hs19C07 most likely increases LAX3-mediated
auxin influx and may provide a mechanism for
cyst nematodes to modulate
auxin flow into root cells, stimulating cell wall hydrolysis for syncytium development.