A Secreted SPRY Domain-Containing Protein (SPRYSEC) from the Plant-Parasitic NematodeGlobodera rostochiensisInteracts with a CC-NB-LRR Protein from a Susceptible Tomato

Abstract

Esophageal gland secretions from nematodes are believed to include effectors that play important roles in plant parasitism. We have identified a novel gene family encoding secreted proteins specifically expressed in the dorsal esophageal gland of Globodera rostochiensis early in the parasitic cycle, and which contain the B30.2/SPRY domain. The secondary structure of these proteins, named the secreted SPRY domain-containing proteins (SPRYSEC), includes highly conserved regions folding into beta-strands interspersed with loops varying in sequence and in length. Mapping sequence diversity onto a three-dimensional structure model of the SPRYSEC indicated that most of the variability is in the extended loops that shape the so-called surface A in the SPRY domains. Seven of nine amino acid sites subjected to diversifying selection in the SPRYSEC are also at this surface. In both yeast-two-hybrid screening using a library from a susceptible tomato and in an in vitro pull-down assay, one of the SPRYSEC interacted with the leucine-rich repeat (LRR) region of a novel coiled-coil nucleotide-binding LRR protein, which is highly similar to members of the SW5 resistance gene cluster. Given that the tomato cultivar used is susceptible to nematode infection, this SPRYSEC could be an evolutionary intermediate that binds to a classical immune receptor but does not yet, or no longer, triggers a resistance response. Alternatively, this SPRYSEC may bind to the immune receptor to downregulate its activity.

The Effector SPRYSEC-19 ofGlobodera rostochiensisSuppresses CC-NB-LRR-Mediated Disease Resistance in Plants

“…Such a mechanism seems to determine the virulence of P. infestans strains on potato plants harboring the RB resistance protein (Chen et al, 2012). Alternatively, as discussed earlier SPRYSEC-19 may also suppress CC-NB-LRR resistance proteins by targeting the immune receptors to the proteasome for degradation (Rehman et al, 2009). However, western blots of total protein extracts of agroinfiltrated leaf areas revealed no enhanced breakdown of CC-NB-LRR proteins or parts thereof in the presence of SPRYSEC-19.…”

“…An in vitro pull-down assay confirmed that SPRYSEC-19 and SW5F-LRR can interact without cofactors (Rehman et al, 2009). This specific association of SPRYSEC-19 and SW5F was confirmed in planta by bimolecular fluorescence complementation (BiFC) and coimmunoprecipitations (Co-IPs; Supplemental Fig.…”

“…Similarly, the physical association of the CC domain of the resistance protein Rpi-blb1 (RB) from potato (Solanum tuberosum) with the IPI-O1 effector of Phytophthora infestans triggers a programmed cell death in Nicotiana benthamiana (Chen et al, 2012). Recently, we found that the effector SPRYSEC-19 of G. rostochiensis interacts in yeast (Saccharomyces cerevisiae) with the seven C-terminal repeats of the LRR domain of the CC-NB-LRR protein SW5F of tomato (Solanum lycopersicum; Rehman et al, 2009). The SW5 resistance gene cluster in tomato confers resistance to a broad range of tospoviruses (Boiteux and de Giordano, 1993).…”

“…SPRYSEC effectors are produced as secretory proteins in the dorsal esophageal gland of G. rostochiensis that is connected via the lumen of the esophagus to the oral stylet (Rehman et al, 2009). They only consist of a SPRY/B30.2 domain, which in many different eukaryotic proteins is involved in intermolecular interactions (Rhodes et al, 2005;Tae et al, 2009).…”

“…Previously, we showed that the effector SPRYSEC-19 of G. rostochiensis interacts with a C-terminal fragment of the LRR domain of SW5F (SW5F-LRR7-13) in a yeast two-hybrid screen on tomato root complementary DNA (cDNA) (Rehman et al, 2009). An in vitro pull-down assay confirmed that SPRYSEC-19 and SW5F-LRR can interact without cofactors (Rehman et al, 2009).…”