Developmental Control and Significance of knotted1 Intercellular Trafficking

Cold Spring Harbor Laboratory, Cold Spg Hbr NY

Investigators

Abstract

The development of a multicellular organism requires careful regulation of protein activity and localization. As genome projects are beginning to reveal the complement of genes required to build a plant, scientists now face the complex issue of where and when genes are expressed and where proteins are localized. Imposed on this complexity is the fact that specific plant gene products traffic between cells through specialized channels called plasmodesmata, so their final location may be distant from the cell where they are made. Specifically, some developmental transcription factors are known to traffic between cells, though little is known of the developmental significance and regulation of this process. This project aims to understand the developmental regulation of cell to cell trafficking of plant proteins, using the KNOTTED1 (KN1) gene as a model system. Dominant Kn1 mutants have non-autonomous effects on cell fate in the maize leaf, and using microinjection assays it was shown that KN1 protein and mRNA can traffic between leaf cells, through plasmodesmata. These assays were constrained by the type of tissue that could be targeted, limiting the ability to ask developmentally relevant questions pertaining to the role of KN1 trafficking in its function for stem cell maintenance. Protein fusions of KN1 to the green fluorescent protein were therefore developed and used to visualize trafficking in vivo in intact plant tissues. In the future research, these studies will be extended to ask significant questions about control of plasmodesmal trafficking in the meristem. Specifically, the size exclusion limit of plasmodesmata in the meristem will be estimated, and the experiments will test if symplasmic domains for protein transport exist. Trafficking signal sequences in KN1 will also be localized. The study will contribute to the understanding of cell to cell communication in plants. It will also increase basic knowledge of plasmodesmata, which are poorly characterized at the molecular level. Plasmodesmata are important for the allocation of photosynthetic products, for plant morphogenesis and for defense against pathogens. Therefore these studies of protein trafficking could have significant implications for improving agricultural productivity.