Postdoctoral Scholars Association

The Type VI secretion system (T6SS) is a toxin-tipped molecular spear used by Gram-negative bacteria to eliminate competitors in the environment. While the structure and function of the T6SS are well understood, less is known about how targeted bacteria can defend against T6SS attack. To investigate mechanisms of T6SS defense, we experimentally evolved eight replicate populations of Escherichia coli under repeated attack by Vibrio cholerae’s T6SS. In just 30 days, evolved populations increased their T6SS survival by an average of 260-fold compared to the ancestor. However, this increase in T6SS survival came at a cost to growth rate, with evolved populations reproducing ~40% as much as the ancestor over the course of one growth cycle. When we further evolved these populations in the absence of T6SS attack, T6SS survival decreased in favor of faster growth. These results indicate that the tradeoff between growth and T6SS survival constrains the evolution of T6SS defense, as defensive mechanisms are not maintained in the absence of T6SS attack. This evolutionary constraint on T6SS defense ensures the continued efficacy of the T6SS as an antagonistic strategy.

Last year, summer drought cost the state over a billion dollars in crop losses. Understanding how plant can cope with this stress is a challenge, but various species in nature are already adapted and have their own mechanisms for combating drought. Native to the American west coast, Mimulus guttatus can survive in Mexican desert, on serpentine rocks, or snow-covered peaks. This suggests that different populations have evolved various resistance mechanisms. Using 29 different populations harvested across California and Oregon, we plan to carry out a genome-wide association study. We want to compare the SNPs present in these populations with their root system architecture phenotype, an analyze of differentially expressed genes and a histological analysis focusing on cell wall compounds such as lignin and suberin. We hope to find new QTLs involved in drought resistance and even shed light new defense mechanisms that could be exported to crops in the future.

Optoretinography has potential to measure photoreceptor function objectively and noninvasively. Its sensitivity to disease-related dysfunction depends essentially on the amount of variation in the responses among cones, individuals, and measurements. Our study uses AO-SS-OCT with 3D cellular resolution to measure phase changes in response to stimulus flashes in the human retina. We aim to quantify these sources of response variation, to establish a reliable baseline for assessing visual dysfunction in clinical populations. Preliminary results are presented here.