Thank you to BlueRidgeKitties@Flickr for contributing photographs to complement today’s entry for the UBC Celebrate Research Week series (original image 1 | original image 2 | UBCBG Botany Photo of the Day Flickr Pool). Much appreciated!
Lindsay Bourque introduces Dr. Li:
Dr. Xin Li is an Associate Professor in the UBC Department of Botany and a research fellow in the Michael Smith Laboratories. Her lab’s research focuses on understanding the innate ability of plants to defend themselves against pathogen infection. Using the model organism Arabidopsis thaliana to understand new regulatory components of plant disease resistance, Dr. Li sees a potential application in environmentally-friendly agricultural disease control. Arabidopsis thaliana is an annual native to most of Europe, Asia and northwestern Africa. It was the first plant genome to be entirely sequenced and was designated as a model organism in 1998. There are several features that make Arabidopsis thaliana (commonly known as thale cress or mouse-ear cress) an ideal model organism, including: a rapid life cycle (about 6 weeks from germination to mature seed), small genome and the availability of mutant lines (hence variation in disease resistance) and genomic resources through Stock Centres.
Dr. Li writes:
Plants have evolved sophisticated disease resistance mechanisms through long history of dealing with microbial pathogen infections. The kind of immunity we study is mediated by resistance proteins (R proteins), which are conceptually similar to animal innate immunity receptors. There are two basic functions of plant R proteins as immune receptors. One is to recognize the presence of the pathogen, and the second is to initiate a robust defense response to fight against the pathogen invasion. The conserved nature of R protein mediated resistance makes it possible to be studied in model plant-pathogen systems where the organisms have short life cycles, are easy to manipulate and have the great benefit of advanced genetic and genomic resources. For higher plants, that choice is Arabidopsis thaliana, the mouse-ear cress model that helps us solve mysteries in plant biology like the fruit fly (Drosophila melanogaster) helps solve questions in animal development. Better understanding of plant R protein mediated immunity will not only help us develop better environmentally friendly disease control strategies in crop fields, but it can also lead to a better understanding of some of the animal immunity mechanisms mediated by receptors similar to R proteins.
In Arabidopsis, there are more than 200 predicted R genes. We previously identified a unique gain-of-function mutant snc1 by chance and it encodes an R gene. Our lab has developed snc1 as an autoimmune model to dissect the molecular events occurring after resistance proteins are activated. In the snc1 mutant, a point mutation resulting in a single amino acid change (glutamic acid to lysine) renders the SNC1 R protein constitutive active without interaction with pathogens. As a consequence of constitutive defense that reallocates resources from normal growth and development, the stature of the mutant plants is dwarf and the morphology sickly. Intriguingly, similar mutations in the same region of mammalian immune receptor Nod2 are also associated with human autoimmune Crohn’s disease. The size of the mutant plants correlates with the level of defense, providing an easy readout of the immune responses (Figure 1).
Daniel adds: In other words, Dr. Li’s lab is tackling the questions: what happens when a resistance protein is activated? What happens when a resistance protein is “always on” or at elevated levels? Even though there are benefits (a correlation between high resistance protein levels and minimal pathogen infection), there are also disadvantages (a negative correlation between high resistance protein levels and typical plant growth). This leads to the next series of questions asked by Dr. Li’s lab: is it possible to grow plants with both high resistance protein levels and still have typical plant growth? If so, how? If successful and the relevant techniques are applied to crops, then it may be possible to have more environmentally-friendly food production, perhaps by reducing pesticide use or increasing yield/ha (and thus not requiring as much land for food production).