David Hannapel received his B.S. In Horticulture from the University of Illinois in 1978 and his M.S. in Horticulture from the University of Georgia in 1981. He received his Ph.D. in Horticulture from Purdue University in 1985. He was a postdoctoral research associate with John Ohlrogge working on fatty acid biosynthesis at the USDA NRRC, Peoria, IL from 1985 to 1987. David has participated in sabbatical leaves in the laboratories of Gerco Angenent, Plant Research International, The Netherlands and Sarah Hake, Plant Gene Expression Center. David is currently a member of the Interdepartmental Plant Biology Major, the Interdepartmental Genetics Major and the Molecular, Cellular, and Developmental Biology Program.
Dr. Hannapel's area of research interest is in developmental biology with a focus on the control of vegetative meristem determination and the role of transcription factors in regulating development. The Hannapel lab is currently investigating the mechanisms that regulate long-distance movement of full-length mRNAs in plants. Focus is on the identification of RNA-binding proteins that regulate RNA stability, movement, and translation repression.
Dr. Hannapel is leading a NSF-funded project to uncover the network of RNA signals and protein chaperones that are responsible for the photoperiod-activated signaling that induces tuber formation in potato. Several approaches are being undertaken to identify and characterize mRNAs and proteins from phloem, including the profiling of RNA expression, proteomics, and RNA/protein binding assays. For more information on this project, please visit our website: http://www.public.iastate.edu/~djh/homepage.html
BEL1-like transcription factors are ubiquitous in plants and interact with KNOTTED1-types to regulate numerous developmental processes. In potato, the RNA of several BEL1-like transcription factors has been identified in phloem cells. One of these, StBEL5, and its Knox protein partner regulate tuber formation by targeting genes that control growth. RNA detection methods and grafting experiments demonstrated that StBEL5 transcripts move across a graft union to localize in stolon tips, the site of tuber induction (Banerjee et al., 2006). This movement of RNA originates in source leaf veins and petioles and is induced by a short-day photoperiod, regulated by the untranslated regions, and correlated with enhanced tuber production. Addition of the StBEL5 untranslated regions to another BEL1-like mRNA resulted in its preferential transport to stolon tips leading to increased tuber production. Upon fusion of the untranslated regions of StBEL5 to a GUS marker, translation in tobacco protoplasts was repressed by those constructs containing the 3´ untranslated sequence (Banerjee et al., 2009). The untranslated regions of the StBEL5 mRNA are involved in mediating its long-distance transport and in controlling translation. The 3´ untranslated sequence contains an abundance of conserved motifs that may serve as binding motifs for RNA-binding proteins. Because of their presence in the phloem sieve tube system, their unique UTR sequences and their diverse RNA accumulation patterns, the family of BEL1-like RNAs from potato represent a valuable model for studying the long-distance transport of full-length mRNAs and their role in development.
A long-distance signal for tuber induction in potato. This signaling pathway is based on the initial transcriptional activation by light (yellow arrows) of the StBEL5 gene in the veins of leaves and petioles (blue). A short-day photoperiod (inductive for tuber formation) facilitates movement of the StBEL5 RNA through the petiole junction into the stem (red arrows). The RNA moves to stolon tips, is translated, and binds to a Knox protein partner (brown line) to regulate transcription of select target genes by binding to the tandem TTGAC motif in the promoter.
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