Cytokinins and source-sink relationships within plants

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Plants are organisms that grow by the constant addition of specialized modules - organs like roots, branches, leaves, stem nodes, flowers and fruits. Obviously the addition and growth rates of the different modular parts must be carefully orchestrated. Like animals, plants use hormones to achieve the appropriate level of organization. One such group of hormones is the cytokinins, a family of about 25-30 related compounds. They are thought to encourage growth by stimulating cells to divide or process sugars more quickly. Cytokinins are very challenging to work with because of the numerous forms and extremely low concentrations at which they operate. I will study how cytokinins direct plant modular growth by perturbing the forms of cytokinins present and the balance of their production using four different systems. We know very little about how the different forms of cytokinin are interconverted; therefore I will be analyzing plants that have been genetically modified to silence genes that are thought responsible for converting high to low activity cytokinins. Secondly, I will use plants genetically engineered to accumulate unusually large concentrations cytokinin specifically in fruits to determine the role of those organs in providing the rest of the plant with cytokinin. Thirdly, to determine the activity levels of different forms of cytokinin in growing seeds, I will investigate their genomic response to forms of cytokinins that they usually do not make themselves. Finally I will investigate the potential impact that fungal infection has on cytokinin production and its role in causing tumors, which are essentially large and unusually strong growing modules. Results will be relevant to agronomists wanting know how to direct more plant resources into seed production, horticulturalists interested in changing traits like investment into branching or flowering or plant pathologists who want to understand infection processes. Above all, it will advance our state of knowledge about how plants grow.