Looking through the open window of root development: understanding how plant hormones position the susceptibility zone in Medicago

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Legumes form beneficial associations with nitrogen-fixing rhizobial bacteria, resulting in the formation of nitrogen-fixing nodules on the roots. This process can only be initiated within a specific zone of the root, referred to as the susceptibility zone. Changes in auxin and cytokinin are necessary and sufficient for nodule organogenesis in a legume and it seems likely that the restrictions in the root zonation that allow nodule development is associated with the status of auxin and cytokinins within the susceptibility zone. Robustness in plant development is associated with tissues tightly coordinating their meristematic, growth and differentiation activities both spatially and temporally. Over the last decade, we have increased our understanding, through a combination of molecular biology and computational modelling, of the establishment and regulation of root meristem zones in Arabidopsis. Particularly important roles have emerged for the hormones auxin and cytokinin. This PhD project will dissect the molecular underpinnings that create the susceptibility zone within the legume root, where nodulation is initiated. The student will make use of the recent advances in understanding of the Arabidopsis root to elucidate the hormonal regulation of the legume susceptibility zone. By adapting the Arabidopsis root computational framework for use in legumes, new hypotheses will be generated to explain the susceptibility zone's regulation. Experimental testing of these hypotheses will add mechanistic insight into how legume root development has been reprogrammed by symbiotic bacteria.