The cytokinins: signaling molecules within plants and among biota.

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Like animals, plants use hormones in their development. The cytokinins, are a family of hormones, which are challenging to work with because of their numerous forms and extremely low concentrations. Over 20 years my lab has shown that cytokinins strengthen the growth of seeds and yield of crops. Along the way, there were things we couldn't explain just with plant physiology. It became apparent that bacteria also made cytokinins and, in some cases, used them to control plant growth. Most curiously, as we kept looking, we found that every different life form we studied, also produced cytokinins. This is the case with fungi, which we also showed can make cytokinins. Initially we believed fungi made cytokinin just to hijack the growth of plants; but, we discovered that all fungi make cytokinins - even those not associated with plants. In this proposal we will find out how cytokinins may control fungal growth itself. To do this, we engineered a fungus (corn smut) so that it can't make cytokinin. Growth of this mutant fungus will be compared to the normal variety to see if these cytokinins may also act as fungal hormones. Furthermore, we will use this system to determine how the pathogenic corn smut fungus and plants "talk" to each other, through cytokinin production, to orchestrate tumor production. In a second project, we will investigate how insects use cytokinin production to cause plant tumors (galls). Our early results indicate that insects make cytokinins regardless of whether they can cause galls; but the ones that make galls have different amounts and types of cytokinin. The difference may be caused by the ability of some insects to associate with cytokinin-producing bacteria. We will test this idea by examining the amounts and types of cytokinin made by gall producing and non-gall producing insect adults and larvae. We will then determine if killing bacteria in the insects with antibiotics will eliminate any of the cytokinin made by insects. The prevalence of cytokinin activity in bacteria, fungi, plants and insects, provokes a question - what is their role in organisms throughout evolution? To answer this, project 3 will work on a slime mold called Dictyostelium. In evolution it sits at a juncture between plants, fungi and animals and can provide insight into the common or diverging roles of cytokinin among kingdoms. In its unusual life cycle, cells can exist separately or assemble to form multicellular organisms. We will study cytokinins as cells organize in these different ways. Cytokinins will be analyzed during the Dictyostelium life cycle in wild-type and mutant strains with altered cytokinin synthesis or metabolism. Overall, these sets of experiments will reveal how "plant" hormones play roles well beyond plants to impact several other forms of life. It will provide a basis for understanding how organisms communicate, which can have impact for how crops grow and how they resist fungal, bacterial and insect pests.