AUTHOR=Zembek Patrycja , Danilecka Aleksandra , Hoser Rafał , Eschen-Lippold Lennart , Benicka Marta , Grech-Baran Marta , Rymaszewski Wojciech , Barymow-Filoniuk Izabela , Morgiewicz Karolina , Kwiatkowski Jakub , Piechocki Marcin , Poznanski Jaroslaw , Lee Justin , Hennig Jacek , Krzymowska Magdalena 

TITLE=Two Strategies of Pseudomonas syringae to Avoid Recognition of the HopQ1 Effector in Nicotiana Species

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00978

DOI=10.3389/fpls.2018.00978

ISSN=1664-462X

ABSTRACT=<p><italic>Pseudomonas syringae</italic> employs a battery of type three secretion effectors to subvert plant immune responses. In turn, plants have developed receptors that recognize some of the bacterial effectors. Two strain-specific HopQ1 effector variants (for Hrp outer protein Q) from the pathovars <italic>phaseolicola</italic> 1448A (<italic>Pph</italic>) and <italic>tomato</italic> DC3000 (<italic>Pto</italic>) showed considerable differences in their ability to evoke disease symptoms in <italic>Nicotiana benthamiana</italic>. Surprisingly, the variants differ by only six amino acids located mostly in the N-terminal disordered region of HopQ1. We found that the presence of serine 87 and leucine 91 renders <italic>Pto</italic>HopQ1 susceptible to N-terminal processing by plant proteases. Substitutions at these two positions did not strongly affect <italic>Pto</italic>HopQ1 virulence properties in a susceptible host but they reduced bacterial growth and accelerated onset of cell death in a resistant host, suggesting that N-terminal mutations rendered <italic>Pto</italic>HopQ1 susceptible to processing <italic>in planta</italic> and, thus, represent a mechanism of recognition avoidance. Furthermore, we found that co-expression of HopR1, another effector encoded within the same gene cluster masks HopQ1 recognition in a strain-dependent manner. Together, these data suggest that HopQ1 is under high host-pathogen co-evolutionary selection pressure and <italic>P. syringae</italic> may have evolved differential effector processing or masking as two independent strategies to evade HopQ1 recognition, thus revealing another level of complexity in plant – microbe interactions.</p>