The role of PLD1 in iron dependent root growth regulation

Iron (Fe) is an essential element for all organisms. Almost all Fe that is available to animals, including humans, is ultimately derived from plants. Consequently, the ability of plants to acquire Fe, especially under Fe-limited conditions is of high practical relevance. While several important regulatory components for Fe homeostasis and Fe deficiency response have been identified, little is known about the underlying genetic mechanisms that coordinate plant growth with Fe availability. Using a genomic wide association (GWA) mapping approach, the host laboratory has identified phospholipase D zeta1 (PLD1) to be a primary candidate gene for underlying natural variation of root growth during Fe deficiency in the model plant Arabidopsis thaliana. Interestingly, PLD1 is known to be involved in root growth responses upon phosphate deficiency (-P), suggesting that biologically relevant crosstalk between -P and Fe might be integrated at the level of PLD1 function. In this project, we will characterize the regulation of PLD1 in root growth during Fe deficiency. The proposed research includes the confirmation of the role PLD1 in Fe deficiency responsive root growth, the analysis of the underlying molecular and biochemical regulation processes, as well as the identification and characterization of the causal PLD1 alleles in this context. Furthermore, the potential integration of -Fe and - P response pathways through PLD1 will be investigated. Overall, this study is expected to identify both, qualitative and quantitative genetic mechanisms of how plants adjust and adapt to nutritional deficiency stress, and will provide excellent starting points for developing crop species with improved tolerance to nutritional deficiencies, enhanced yields and mineral nutrition under limited growth conditions.

Natural phenotypic variation is one of the most common biological phenomena. For example, notable variation is apparent in diverse species and traits such as human height and disease susceptibility, or crop yield. Phenotypic variation among and between populations is critical for a plant species survival and success. For crops, this also provides important genetic materials for scientific research activities and the breeding of new varieties. Phenotypic variation is the consequence of genetic variation interplaying with environmental factors. One important factor for plant growth is the availability of nutrients, and one very limiting nutrient is iron (Fe). Fe is an essential element for plant and human and of crucial importance for redox regulation, oxidative stress and cell death in both animals and plants. Fe deficiency occurs in aerated alkaline soil and causes reduced plant growth and poor nutritional value of crop food. On the other hand, Fe toxicity is one of the most limiting factors for plant growth in flooded soils especially in African rice paddies. The plant tolerance of Fe toxicity varies greatly at intraspecies or interspecies levels. However, it is unknown which genetic loci and molecular mechanisms lead to plant tolerance to Fe toxicity. In this project, we identified S-nitrosoglutathione reductase (GSNOR), a common nitric oxide (NO) signaling regulator in both plants and animals, as a major locus to control the root growth tolerance to high Fe by using genome-wide association studies of natural population of Arabidopsis thaliana. Natural GSNOR variants cause variation of root growth sensitivity to Fe toxicity through transcription regulation. Moreover, we discovered that the function of GSNOR for Fe tolerance is conserved in the legume plant Lotus japonicus. We further discovered that Fe accumulation is essential for both nitrosative and oxidative stress to cause growth inhibition and cell death in root tips. Overall, we identified the first gene that underlies Fe tolerance of root growth, as well as the underlying molecular mechanisms. In the future these results could lead to the development of Fe resistant crops and could help to increase productivity in flooded soils.