It’s Getting Hot in Here: The Convergence of PIF4 and Temperature in Regulating Immunity and Disease Chlorosis in Arabidopsis thaliana

With the advent of increasing global temperatures due to climate change comes greater susceptibility of our staple crops to environmental stressors and disease vectors. Once these crops express symptom development, such as chlorosis, they are no longer considered viable products in the consumer market, contributing to agricultural and financial losses. We believe that PIF4 – a repressive transcription factor regulated by the activity of phytochrome B, a photoreceptor and thermosensor – may be at the nexus of a growth/defense trade-off observed at higher temperatures in many crops. Though confirmed to be a positive regulator of plant growth, there are conflicting reports identifying PIF4 as a negative regulator of immunity. These stark contrasts are likely due to the different methods used during bacterial inoculation. Since methods employing spray or dip inoculation are effective at eliciting a response from PIF4, we hypothesize that the mechanism of PIF4-mediated immune response is localized to the guard cells. To confirm this hypothesis, we analyzed the impact of PIF4 expression specifically in the guard cell on plant growth and plant immunity. This was accomplished by assaying growth – via hypocotyl and petiole – and stomatal aperture. Additionally, we examined disease symptoms and resistance in pif4-1 null mutants and mutants in the pif4-1 background that express PIF4 under its native promoter or a guard cell-specific promoter. Furthermore, we hypothesize that PIF4 acts as a negative regulator of SGR1, which is critical for the development of leaf chlorosis and may operate independently of PIF4’s involvement in immunity – this research is ongoing.

My overall experience here at Cornell has been pleasantly surprising. Perhaps most surprising is how social and scenic the city of Ithaca is – with its beautiful gorges, great food, and fun urban areas, I haven’t had a moment this summer that I won’t reminisce upon fondly. In regard to my REU, the program and my research project have been valuable experiences for me. My exposure to new ideas, perspectives, and techniques has been an essential component of my academic growth, and I will always treasure the personal and professional network I have built here. Working with a new mentor and lab has been very insightful and integral to my decision to commit to my graduate education – my Cornell lab was so different in the best way possible. I highly recommend this program to anyone considering a career in academic research.