Identification and characterization of the Arabidopsis thaliana PT11 multigene family

Abstract

Plants possess a complex network of signalling pathways to integrate environmental and developmental cues. Kinases play a central role in this process by linking inter and intracellular signals to downstream adaptive responses. Pto-Interacting 1-like (PT11) kinases represent a specific class of serine/threonine protein kinases involved in biotic stress signalling, that are also emerging as players in abiotic stress response or plant development. Little is known, however, about their precise functions. This study describes the identification and characterization of PT11-like genes in Arabidopsis thaliana. A specific signature motif identified from previously characterised PT11 kinases is used as a bait to retrieve 8 putative PT11 sequences in Arabidopsis. Phylogenetic analysis reveals that these PT11 isoforms group into 4 pairs of paralogs that likely arose from a relatively recent duplication event. These genes are shown to vary in their expression patterns, during plant development and in response to both biotic and abiotic stresses, suggesting expression divergence as a possible driving force for the expansion of the family in Arabidopsis. Using indexed T-DNA insertion mutants and silencing lines, non-redundant biological functions are demonstrated for two PT11-like genes. Silencing of PT11-8 promotes root elongation in young seedlings, through an increase in root meristem size, which identifies that isoform as a negative regulator of root development and cell production rates. Another PT11 isoform, PT11-5, is shown to suppress plant basal resistance to the bacterial pathogen Pseudomonas syringae pathovar tomato (Pst) DC3000. PTII-5 loss-of-function leads to impaired growth of virulent Pst DC3000 pathogen in planta, as verified by two independent bacterial quantification methods. The oxidative signal-inducible 1 (OXI1/AGC2-1), known as an upstream component of ROS-dependent responses, is identified as a direct protein interacting partner of PTI1-5. OXI1 is known to interact with 4 other PTI1-like kinases and circumstantial evidence from this thesis suggests its likely involvement with a sixth isoform, PTI1-8, in regulating root elongation. Based on these experimental data, a general model for PTI1 signalling is proposed in which individual isoforms have evolved to transduce diverse upstream endogenous or exogenous cues through the OXI1-mediated ROS signalling pathway. Show more