Networking for Plant Survival

The Faculty of 1000 is an innovative Web-based literature awareness tool published by BioMed Central. This new research service provides scientists with a continuously updated insider's guide to biology's most important papers, based on the recommendations of a faculty of more than 1,400 selected leading researchers. Each month these scientists review two to four of the most noteworthy papers they have read, which may or may not be authored by F1000 members, and post evaluations and comments on the Faculty of 1000 Web site. The reviews are organized by topic, so users can easily find articles in their particular field. Each specialty area has a Top 10 list, indexing the most highly rated articles in that field over the previous month. This list is updated daily. Only articles that have been actively picked in the preceding month are listed. A general Top 10 lists the hottest papers overall. Each issue, The Scientist will publish a given research area's Top 10, as well as a short review of one or more of the listed papers. We will also publish a selection of comments on interesting papers outside of the Top 10, culled from the Faculty of 1000's output. For more information visit www.facultyof1000.com. Long ago, viruses learned how to modify plasmodesmata to facilitate movement of their genomic RNA between cells. For years, botanists wondered if these pathogens had invented a new mechanism, or had hijacked an endogenous one that let the cells communicate developmentally important information like nucleic acids and proteins. Accumulating research, including a new study from Philip Benfey's laboratory at New York University, indicates that the latter is the case.1 F1000 Top 10 All of Biology 1. K. Nakajima et al., "Intercellular movement of the putative transcription factor SHR in root patterning," Nature, 413:307-11, Sept. 20, 2001. 2 G. Chang, C.B. Roth, "Structure of MsbA from E. coli: A homolog of the multidrug resistance ATP binding cassette (ABC) transporters," Science, 293:1793-1800, Sept. 7, 2001. 3. A.C.R. Epstein et al., "C. elegans EGL-9 and mammalian homologs define a family of dioxygenases that regulate HIF by prolyl hydroxylation," Cell, 107:43-54, Oct. 5, 2001. 4. M.K. Raghuraman et al., "Replication dynamics of the yeast genome," Science, 294:115-21, Oct. 5, 2001. 5. S. Etienne-Manneville, A. Hall, "Integrin-mediated activation of Cdc42 controls cell polarity in migrating astrocytes through PKC*," Cell, 106:489-98, August 24, 2001. 6. J. Parkhill et al., "Complete genome sequence of a multiple drug resistant Salmonella enterica serovar Typhi CT18," Nature, 413:848-52, Oct. 25, 2001. 7. Y.F. Zhou et al., "Chemistry of ion coordination and hydration revealed by a K+ channel-Fab complex at 2.0 A resolution," Nature, 414:43-8, Nov. 1, 2001. 8. J. Dubrulle et al., "FGF signaling controls somite boundary position and regulates segmentation clock control of spatiotemporal Hox gene activation," Cell, 106:219-32, July 27, 2001. 9. J. Zakany et al., "Localized and transient transcription of Hox genes suggests a link between patterning and the segmentation clock," Cell, 106:207-17, Sept. 21, 2001. 10. J.P. Xiong et al., "Crystal structure of the extracellular segment of integrin alpha Vß3," Science, 294:339-45, Oct. 12, 2001. In an article that ranked #1 in the Faculty of 1000 "All of Biology" Top 10 list for Dec. 1, 2001, Benfey's team showed that a protein called SHR has dual functions: it promotes precursor cell division, then helps specify the progeny's developmental fate. Based partly on evidence from other laboratories, the researchers think SHR moves through plasmodesmata between cells. Plasmodesmata are 60-nm-wide, membrane-bound channels that link plant cell cytoplasms across cell walls. Like gap junctions between animal cells, plasmodesmata provide a route for ions and small molecules to move between cells. Just behind the growth-originating meristem at the root tips, adjacent tissues rapidly specialize while connected by plasmodesmata. Benfey's team asked whether these tiny pores carry signals by which one cell controls the fate of another, thereby coordinating the complex tissue patterning in roots. The answer, they concluded, seems to be yes. Using mutants of the tiny mustard plant Arabidopsis, plus specially constructed reporter genes, tissue-specific antibodies, and genetic crosses, the researchers discovered that SHR, which serves as a gene-activating transcription factor, moves from the central, stelar cells of the root tip to an adjacent cell layer, which divides longitudinally. The two new layers then specialize in very different ways, one becoming endodermis and the other cortex. Precursor cells in mutants defective in SHR fail to divide, while plants making extra SHR produce additional cell layers, all of which take on endodermal properties. Occasional SHR expression at the root surface overrides cell specification as epidermis. SHR doesn't work alone--it requires a related transcriptional factor called SCR in adjacent cells. Like all multicellular organisms, plants need a way for their cells to communicate, to coordinate developmental events such as flowering for example, or to orchestrate organism-wide defense mechanisms against pathogens. Much of this long-distance information trafficking occurs in sieve tubes, which rely on modified plasmodesmata. Benfey's team helped define local, cell-to-cell interactions among and within tissues. 'To my knowledge, this is the first case in which a transcription factor has been shown to move between cells and for which the biological relevance is known," says Benfey. "It adds a new means of cell-cell signaling to previously known mechanisms." Barry A. Palevitz (palevitz@dogwood.botany.uga.edu) is a contributing editor. 1. K. Nakajima et al., "Intercellular movement of the putative transcription factor SHR in root patterning," Nature, 413:307-11, Sept. 20, 2001.

Networking for Plant Survival

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