Plants adjust their development to the environmental conditions. This incredible flexibility is exhibited in tropic responses, like phototropism, but also extends beyond the individual organ scale. In Jukowska lab we are interested in how environmental stress shapes plant architecture. Stress exposure often induces quiescence of growth through modification of cell cycle activity, cell expansion and cell wall extensibility. The period of initial growth arrest and the extent of recovered growth differs between individual organs leading to altered plant morphology. So far we studied altered morphology of Root System Architecture, by capturing growth dynamics in simple descriptive models, like Root-Fit (Julkowska et al., 2014). By examining natural variation therein we identified four distinct responses, which correspond to maintenance of ion equilibrium in shoot tissue. When Root System Architecture data was used for Genome Wide Association Studies (GWAS), we were able to identify a number of novel candidate genes as well as genes previously linked to salinity tolerance, for which we unravelled their role in root development (Julkowska et al., 2017). Our results show how study of growth dynamics leads to novel trait discovery, which is especially relevant in these times of fast development in plant phenotyping approaches.
Current focus of Julkowska lab is studying the salt-induced changes in whole plant morphology of model plant Arabidopsis, as well as salt stress-induced changes in root system architecture in Arabidopsis and environmentally resilient wild tomato, Solanum pimpinellifolium.
Salt-induced changes in root architecture of wild tomato S. pimpinellifolium
Solanum pimpinellifolium is the closest relative to cultivated tomato and it is native to west coast of South America. Different accessions of S. pimpinellifolium were collected from a wide variety of habitats, and in previous studies they were observed to show diversity in their salt stress response in the shoot growth and transpiration (Morton et al., in preparation). We explored this population of 260 S. pimpinellifolium accession for variation in root architecture and salinity induced changes therein and observed that within our population there are profound differences in root architecture ideotypes. Currently, we are performing GWAS to identify underlying candidate genes. We also are performing transcriptomic studies and network analysis to identify the gene networks that will inform identification of the developmental mechanisms underlying the different ideotypes.
How salt stress affects root-to-shoot ratio?
Notably, salt stress rapidly impacts the growth and development of different plant organs to different extents, leading to alterations in plant development. In Arabidopsis Col-0 genotype, reduction in main root growth is more severe than reduction in lateral root growth or development, resulting in altered root architecture. Other alterations to plant development, such as root-to-shoot ratio are likely to contribute to salinity tolerance. We studied how salt affects root-to-shoot ratio in Arabidopsis plants grown on agar plates, by quantifying the dynamics of root and shoot growth in different conditions. We developed a tool that enables estimation of increases in root and shoot mass through quantification of green and white pixels and automated fitting of exponential growth curves. The identified genetic components underlying salt stress-induced changes in root-to-shoot ratio included DUF247, encoding Domain of Unknown Function. Currently, we are examining the function of DUF247 genes by generating and examining DUF247 mutants and overexpression lines. Fluorophore fused protein constructs and GUS reporter lines are being generated to provide further insight into tissue specific expression and sub-cellular localization of DUF247. We are also exploring the function of individual DUF247 protein domains.
Molecular mechanisms underlying reduced lateral root development in UAS-HKT1 lines
In our previous study, we discovered that high expression of Arabidopsis High Affinity K+ Transporter (HKT1;1), sequestering sodium from the transpiration stream in root pericycle, results in increased salinity tolerance (Julkowska et al., 2017). Pericycle specific overexpression of HKT1 resulted in reduced lateral root development under saline conditions. Interestingly, this effect seems to be specific to dicot species, as wheat lines with high HKT1 expression do not show reduction in secondary lateral roots. We examined the transcriptional changes underlying altered lateral root development downstream of HKT1 through comparative transcriptomic analysis of two lines with stelar overexpression of HKT1. Among the transcripts that were expressed differentially between UAS-HKT1 overexpression lines and their background lines, we found genes involved in cell differentiation, ABA signaling and ion transport. Further validation of identified candidate genes using CRISPR-Cas9 knockouts and overexpression lines is ongoing, and will enhance our understanding of processes controlling plant development under abiotic stress conditions and the importance of root architecture for salinity tolerance.
Other germinating projects
- Heat and drought stress responses in Arabidopsis and tomato
- Developing pipelines for efficient and reproducible data analysis from high-throughput phenotyping setups
- Developing new phenotyping methods to better describe architecture of above and below-ground organs
- Studying the contribution of leaf morphology to photosynthetic efficiency and transpiration use efficiency
- Boyce Thompson Institute is excited to welcome Magdalena Julkowska to Ithaca, where she becomes our newest Assistant Professor. Magda’s main research focus is how environmental stress affects plant development and […] Read more »