“Towards a Rather Incomplete Understanding of the Genetics of Maize Resistance and Defense Response.”
Title: Towards a Rather Incomplete Understanding of the Genetics of Maize Resistance and Defense Response
On October 4th, Dr. Peter Balint-Kurti of USDA-ARS presented a seminar titled “Towards a Rather Incomplete Understanding of the Genetics of Maize Resistance and Defense Response.” Dr. Kurti is a research geneticist who has previous experience in the biotechnology industry. He began his seminar by describing the ways in which plants defend themselves from pathogenic fungi. First of all, he explained that the characteristics of a plant, such as its cuticle thickness or trichome density, play a role in susceptibility to diseases. If a pathogen persists despite these characteristics, the plant can respond to a pathogen with two types of responses: Pathogen associated molecular pattern triggered immunity (PTI) and effector triggered immunity (ETI). PTI is a symptomless basal resistance while ETI usually results in a hyperimmune response like programmed cell death, where the plant kills an infected cell to prevent an infection from spreading. Next, Dr. Balint-Kurti gave examples from his research, showing how he is investigating which genes and quantitative trait loci (QTLs; areas of genomes) are conferring resistance to diseases on maize leaves. By comparing the genomes of disease-resistant lines of maize to disease-susceptible lines, he was able to find QTLs highly associated with disease resistance. Further research used crosses of a highly characterized germplasm of maize called the Nested Associated Mapping Population to delineate the resistance-conferring region with greater specificity. This narrowed the possibilities to a single QTL containing three genes. They took disease-susceptible and disease-resistant lines and looked at the expression of these genes with and without an infection. With infected-resistant lines, the expression of a single gene increased, giving evidence to its association with resistance. Furthermore, an increased expression of this gene was shown to have more disease-resistance. Dr. Balint-Kurti framed the question as to why wouldn’t all maize naturally express this gene at a high level. It turns out that in the absence of disease pressure, maize lines with little or no expression of the resistance gene tended to have better yield. He gave another example of this phenomenon with maize lines that have varying amounts of leaf flecking, or tiny necrotic spots. The amount of flecking was related to the level of disease resistance. Lines with more flecking tended to have a higher level of disease resistance, however, these lines had less yield in the absence of disease pressure. This is possibly partly due to less surface area of the leaves available for photosynthesis. He said that a compromise could be reached by selecting for lines with moderate amounts of flecking. In future work, Dr. Balint-Kurti aims to continue the investigation of disease resistance mechanisms.
By Scott Cosseboom
