Text by Eve Kaurilind
I joined to Prof. Ülo Niinemets group three months ago. Previously I studied stomatal function and structure in response to light and elevated CO2 during my master and PhD thesis at University of Tartu. I have always included myself to group of “Arabidopsis haters” but after postdoctoral grant “Regulation mechanism of abiotic stress responses” at University of Helsinki with supervisor Dr. Mikael Brosché, I started to love this miserable tiny species. I will continue my research on plant abiotic stress responses related to hormonal regulation and phenotyping based on ecophysiological methods.
Citation: Kaurilind, E., & Brosché, M. (2017). Stress Marker Signatures in Lesion Mimic Single and Double Mutants Identify a Crucial Leaf Age-Dependent Salicylic Acid Related Defense Signal. PloS one, 12(1), e0170532. (link to full text)
Plants experience altered environmental conditions during growth. Thus, the stress of any type may lead to either plant acclimation or premature ageing and finally death. The question whether a cell should live or die is fundamental to survival of the plant. Programmed cell death (PCD) is activated by reactive oxygen species (ROS) and the life-span of ROS signals is controlled by antioxidants. The catalases detoxify hydrogen peroxide to water and oxygen in the peroxisome. The Arabidopsis cat2 mutant is deficient one of the main ROS scavenger CATALASE2, and develops lesions that are day length and light intensity dependent. Even though cat2 plants experience chronic oxidative stress, the five weeks old plants start to lose the misregulated cell death phenotype which implies the ability to acclimate to intracellular stress conditions. A multitude of different signal molecules are involved in defense signaling in addition to ROS and includes several plant hormones. A challenge in the study of defense signaling is the many roles of hormones and their synergistic and antagonistic interactions. In this study, we aimed to identify age related regulatory mechanisms responsible for signaling during abiotic stress that subsequently leads to plant acclimation. We found that both auxin and salicylic acid signaling are important regulators of defense gene expression in leaves of different age classes.
Plants are exposed to abiotic and biotic stress conditions throughout their lifespans that activates various defense programs. Programmed cell death (PCD) is an extreme defense strategy the plant uses to manage unfavorable environments as well as during developmentally induced senescence. Here we investigated the role of leaf age on the regulation of defense gene expression in Arabidopsis thaliana. Two lesion mimic mutants with misregulated cell death, catalase2 (cat2) and defense no death1 (dnd1) were used together with several double mutants to dissect signaling pathways regulating defense gene expression associated with cell death and leaf age. PCD marker genes showed leaf age dependent expression, with the highest expression in old leaves. The salicylic acid (SA) biosynthesis mutant salicylic acid induction deficient2 (sid2) had reduced expression of PCD marker genes in the cat2 sid2 double mutant demonstrating the importance of SA biosynthesis in regulation of defense gene expression. While the auxin- and jasmonic acid (JA)- insensitive auxin resistant1 (axr1) double mutant cat2 axr1 also led to decreased expression of PCD markers; the expression of several marker genes for SA signaling (ISOCHORISMATE SYNTHASE 1, PR1 and PR2) were additionally decreased in cat2 axr1 compared to cat2. The reduced expression of these SA markers genes in cat2 axr1 implicates AXR1 as a regulator of SA signaling in addition to its known role in auxin and JA signaling. Overall, the current study reinforces the important role of SA signaling in regulation of leaf age-related transcript signatures.