Plant shape or architecture has a major impact on agricultural yields. Architecture is the end product of morphogenesis, which in plants, as in animals, commences during early embryogenesis with the development of distinct organ and tissue types. Plant development proceeds through the continuous initiation of organs from groups of stem cells called meristems. All of the shoot organs, such as leaves and flowers, are initiated from the shoot meristem in regular patterns known as phyllotaxies. How these patterns are generated has been a subject of interest for centuries, and has been of interest to mathematicians, physicists and biologists. Initiation of organs in regular patterns can optimize light capture for efficient photosynthesis, and in some plants generates architectural support. In this proposal Dr. Jackson will study the ABPHYL1 (ABPH1) gene of maize. Loss of ABPH1 function causes plants to develop with opposite and decussate phyllotaxy rather than the alternating or distichous pattern that is normal for maize. The ABPH1 gene encodes a cytokinin inducible response regulator homolog, and though this gene family has been known for several years this is the first report of a loss of function phenotype in one of these genes. Response regulators were first discovered in bacteria and function in signaling pathways. Therefore these studies will investigate the link between a unique developmental question and a novel function for a gene predicted to transduce cytokinin signals in plants. In particular, the expression of ABPH1 protein and mRNA will be described in relation to its role in phyllotaxy, and the effect of cytokinins on its expression will also be documented. The hypothesis that cytokinins may regulate phyllotaxy will also be tested, by growing shoot explants or embryos on medium containing exogenous cytokinin. Finally, microarray analysis will be used to identify genes that are regulated by ABPH1, and some of these will be characterized by genetic analysis. These studies should contribute to several areas of biology, including developmental regulation, morphogenesis, signaling and activity of growth regulators. Importantly, they should foster interactions between hormone biologists and developmental biologists. The proposed studies will also be of interest to researchers in other disciplines, such as mathematics and biophysics.
