Cytokinin-mediated processes promote heat-induced disease susceptibility of Arabidopsis to Pseudomonas syringae pv. tomato
Alexandra Shigenaga: Colorado State University
<div>Under increased temperatures, such as those predicted as a result of global climate change, plant defense responses are attenuated leading to a process known as heat-induced disease susceptibility. The plant growth hormone cytokinin regulates responses to both biotic and abiotic pressures. To address the role of cytokinin in heat-induced susceptibility of <em>Arabidopsis</em> to the bacterial pathogen <em>Pseudomonas syringae</em> pv. <em>tomato</em> (<em>Pst</em>), wild-type plants and a cytokinin receptor mutant (<em>ahk2,3</em> mutated on <em>ARABIDOPSIS HISTIDINE KINASE</em> <em>2</em> and <em>3</em>) were exposed to the pathogen at two different temperatures, normal (22°C) and high (28°C). <em>Pst</em> populations were measured to assess pathogen fitness and host susceptibility. Stomatal conductance and gene expression were also measured to evaluate how lack of cytokinin signaling impacts the ability of plants to respond to simultaneous biotic and abiotic pressures. We found that <em>ahk2,3</em> plants were less susceptible at 28°C, with <em>Pst</em> populations plateauing at 36 hours post inoculation in <em>ahk2,3</em>. Moreover, pathogen-induced stomatal closure was impaired under heat stress and expression of genes associated with defense or nutrient transport were also affected. This suggests that cytokinin promotes physiological conditions that contribute to pathogen proliferation and highlights the value of cytokinin-based chemical and genetic approaches to understand plant susceptibility and improve crop protection under increased temperatures.</div>
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