Seldon Kwafo
Seldon Kwafo
Year: 2019
Faculty Advisor: Jian Hua
Mentor: Leiyun Yang

Determining the noncanonical function of Structural Maintenance Chromosomes 5 (SMC5) in plant innate immunity

Plant immunity studies are characterized by making sense of the structure/function of genes that regulate innate immunity. The SMC5/6 complex has been found to play a role in DNA damage repair in fungi and animals. Studies in Arabidopsis thaliana have indicated that besides the canonical function in DNA damage repair, the SMC5/6 complex plays roles in developmental regulatory pathways, reproduction, as well as biotic and abiotic stress responses. Recent studies have identified the potential of the SMC5/6 complex in regulating immune response pathways, but the mechanism of regulation remains unclear since the homozygous smc5 mutant is embryo lethal and does not produce viable seeds for further studies.

From genetic screens, the weak allele smc5-3 mutant showed involvement in regulating plant immune responses. The mutant exhibits pleiotropic growth phenotypes, such as small leaves and short roots partially due to upregulation of immunity. To understand what and how the smc5-3 mutant regulates immune response we hypothesised that nucleotide-binding leucine-rich repeats (NLRs) may be activated causing it to show the growth phenotype. To contribute to the comprehensive analysis of smc5-3, I did a characterization of smc5-3 by observing the growth phenotype (shoots and roots) and immune response phenotype through a pathogen growth assay using Pseudomonas syringae DC 3000 to elucidate that smc5-3 has increased disease resistance. To detect hydrogen peroxide, the signaling molecule produced during immune responses, in mature Arabidopsis rosette leaves I used 3,3′-diaminobenzidine (DAB). The smc5-3 mutant displayed a higher accumulation of Hydrogen peroxide compared to the wildtype.

In addition, since Phytoalexin Deficient4 (PAD4) is involved in the upregulation of immune responses, I investigated the contribution of PAD4 in smc5-3. We observed that the dwarf phenotype of the smc5 mutant can be partially suppressed in the pad4 smc5 double mutant. Which indicated that means the growth phenotype of smc5 is not totally dependent on the up-regulation of immunity. These analyses confirm that SMC5 does play a role in regulating plant immune responses. Aside from the fine-tuned immune system- studies have shown that plant immune system can be lopsided through misregulated NLRs producing autoimmunity with negative effects on plant growth and fitness without the presence of a pathogen. Therefore, I assisted in transforming the smc5-3 mutant with 108 dominant-negative (DN) Arabidopsis NLRs which will be screened in future experiments to identify which NLRs are activated in smc5-3 to verify if the upregulation of these NLRs is responsible for the growth defect phenotype.

My Experience

I don’t know if you remember how when we were younger the summers all lasted forever? When days disappeared into weeks, weeks disappeared into months. I wish I could hold that feeling forever. This summer felt exactly like that. Every moment in Ithaca has been priceless. From the seminars to learning about science communication and bees as well as outreach projects and getting to know my fellow interns. I would say applying to the Boyce Thompson Institute for Plant Research was the best decision. I came in with no clear expectations of how this internship will turn out. I left everything to chance and gaining new experiences in plant biology. Haven worked in a lab that was investigating abiotic stresses on crop physiology last summer, this internship was the deciding factor on my career path in plant biology and crop science. I’m grateful that I got the opportunity to be a part of the BTI intern group. Working in the Hua lab at Cornell University under the mentorship of Leiyun Yang has been more than rewarding. She provided me with the learning tools to understand plant immunity, which I had no knowledge of prior to joining the lab. The collaboration with my mentor has affirmed my interest in furthering my knowledge in plant biology and contributing to the never-ending expansion of scientific inquiry.