The pervasive impact of cytokinins: signaling within plants and among biota.

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Like animals, plants use hormones to orchestrate development and assembly of their organs like: roots, branches, leaves, stem nodes, flowers and fruits. One group of hormones, known as the cytokinins, is a family of about 25-30 related compounds, which are are very challenging to work with because of the numerous forms and extremely low concentrations at which they operate. Because of their possible potent influence over seed growth they are strong candidates for increasing crop yield. To help evaluate this potential, we will see how cytokinins help seeds form and develop in Brachypodium, a genetic model plant related to cereals like oats and wheat. This will be done by engineering genes that are responsible for making, degrading or activating cytokinins in young seeds. The transgenic seeds have either higher or lower than normal cytokinin activity and will reveal whether cytokinins promote or inhibit seed growth, and possibly yield. Curiously our lab has found that fungi can make plant hormones, including the cytokinins. Although they make them to hijack the growth of plants, we discovered that even fungi, not associated with plants, make cytokinins. To find out how they might affect fungal growth itself, we have genetically engineered a fungus (corn smut) so that it can no longer make cytokinin. Growth characteristics of this mutant fungus will be compared to the normal variety to see if these cytokinins may also be fungal hormones. Lastly 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 in fact be caused by the ability of some insects to associate with bacteria which also make several types of cytokinins. 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. Furthermore we will determine if killing bacteria in the insects with anitbiotics will eliminate any of the cytokinin made by insects. These sets of experiments will reveal how "plant" hormones impact well beyond plants to influence many other forms of life.