The water soaking caused by the TAL effector AvrHah1 involves cell wall modification and may elucidate a role for lesion development during bacterial spot of tomato
A. SCHWARTZ (1), R. Morbitzer (2), T. Lahaye (2), B. Staskawicz (1) (1) University of California, Berkeley, U.S.A.; (2) University of Tübingen, Germany

AvrHah1 is a Transcription Activator Like (TAL) effector in Xanthomonas gardneri (Xg) that induces water-soaked disease lesions on fruits and leaves during bacterial spot of tomato. We observe that water droplets on the surface of a leaf infected with Xg, but not XgΔAvrHah1, are drawn into the leaf through a wound and spread in the apoplast away from the point of entry, conferring a dark, water-soaked appearance. The absence of AvrHah1 decreases the bacterial population present on the surface of infected tomato leaves, however it does not reduce in planta growth. Thus, the role of AvrHah1 may be to increase bacterial exudation from the apoplast. AvrHah1 activates many gene targets in tomato. We selected several highly upregulated candidates (identified using RNA-seq) and explored their contributions to water soaking via heterologous protein delivery, where candidate targets are delivered as protein effectors, and by delivery of designer TAL effectors (dTALEs) targeting candidate gene promoters. We have found that delivery of a tomato pectate lyase via XgΔAvrHah1, but not a pectate lyase catalytic mutant, partially complements water soaking. Furthermore, silencing of the pectate lyase reduces Xg water soaking in tomato. Interestingly, two transcription factor targets of AvrHah1 are able to activate the pectate lyase promoter in transient assays. Understanding lesion development may improve the design of disease tolerant crops by reducing pathogen transmission.

Abstract Number: P9-302
Session Type: Poster