A Pathogen’s Battle to Bend Arabidopsis: Linking Phototropism to Defense Signaling

Slaughter

Mariesa Slaughter
Advisor - Véronique Delesalle

The sessile nature of plants increases their susceptibility to environmental factors. Overexposure to light induces stress, which can lower the plant’s immune system and make it more susceptible to pathogen attacks.  Plants respond to light through photoreceptors, such as phototropins (blue light photoreceptors). These receptors are responsible for responses that aid in the optimization of a plant’s photosynthetic efficiency. Plants have evolved an intricate immune system in order to resist pathogens. Effector-triggered immunity (ETI) allows plants to detect and respond to the presence of a pathogen effector by producing resistance (R) proteins. In Arabidopsis there are approximately 150 R-genes encoding nucleotide binding site (NBS) and leucine-rich repeat (LRR) domain-containing proteins. Many of these R-genes belong to the Toll/Interleukin-1 receptor (TNL) class. Recently, a protein containing a TNL was shown to interact with PHOTOTROPIN-1, suggesting a correlation between defense and light signaling proteins. To help discern the association between these signaling pathways, Arabidopsis thaliana defense signaling mutants were analyzed for altered phototropic phenotypes when exposed to unilateral blue light.  In this experiment eleven Arabidopsis mutant lines (G4X, RLD, rps6-1, phot1-5, snc1-11, srfr1-4, snc1-11/srfr1-4, eds1-2, eds1-2/srfr1-4, rps6-3, and rps4-2) were exposed to unilateral blue light for four hours at which time the angle of curvature was measured to evaluate the phototropic response. Mutants lacking the resistance protein RPS6 demonstrated increased phototropism, while those lacking the resistance protein RPS4 exhibited decreased phototropism.  These results suggest a correlation between a plant’s light receptors and defense signaling TNL proteins.