TRENDS in Plant Science Vol.7 No.9 September 2002 http://plants.trends.com 1360-1385/02/$ – see front matter © 2002 Elsevier Science Ltd. All rights reserved. PII: S1360-1385(02)02316-6 381 Research Update Meeting Report 17th Long Ashton International Symposium, 15–17 April 2002, Bristol, UK. Published online: 12 August 2002 Long Ashton Research Station is due to close in 2003, making this the last in the 35-year symposium series. The wide- ranging theme of the meeting was chosen to highlight the exciting impact that molecular genetics is having at all levels of plant science, ranging from cellular signalling and developmental pathways to natural variation and evolution of plant communities. These new insights are beginning to show how different processes are highly inter-related and how they affect form and function of the whole organism in response to changing environmental factors. Although much fundamental knowledge has been gained from studies on Arabidopsis, a challenge remains to translate this information into beneficial traits in crop plants, including the major cereals. Signalling mechanisms Xing-Wang Deng (Yale University, New Haven, CT, USA) described how photomorphogenesis in Arabidopsis is negatively regulated in the dark by COP1, an E3 ubiquitin ligase, which targets transcription factors, such as HY5 and HYH, for degradation. COP1 is inactivated in the light by direct interaction with the cryptochrome blue- light receptors and its action is regulated by the COP9 signalosome, a multi- protein complex that might have an important function in E3 ligase-mediated signalling in multi-cellular organisms. Peter McCourt (University of Toronto, Canada) questioned the tissue specificity of developmental regulators, such as ABI3 and FUS3, which were thought to be involved only in embryo development. For example, ABI3 is expressed also in the pericycle cells that give rise to root primordia and might, thus, function in lateral root formation. These transcription factors might primarily be regulators of vegetative development that were ‘co-opted’ to an embryo function. The theme of protein degradation in signalling was also discussed by Tai-ping Sun (Duke University, Durham, NC, USA) in relation to gibberellin action. Gibberellins suppress the action of RGA (repressor of ga1-3) and related proteins that repress gibberellin-mediated development. RGA is localized in the nucleus and is rapidly degraded in the presence of gibberellin, a process that requires the presence of the 17-amino acid DELLA motif near the N-terminus. RGA accumulates in the presence of a proteasome inhibitor and in the sleepy1 GA-insensitive mutant, which might thus be defective in protein degradation. Another recurring theme in plant signal transduction is the interaction between plant signalling pathways, as discussed by Sjef Smeekens (University of Utrecht, The Netherlands). The SUN6 gene of Arabidopsis, which is involved in hexose kinase-mediated sugar sensing, is identical to ABI4, a component of the abscisic acid signalling pathway. Ethylene has also been shown to impinge on this pathway, which is important in assimilate availability and nitrogen assimilation. Ben Scheres (University of Utrecht, The Netherlands) discussed the control of cell fate within the Arabidopsis root. Expression of SCARECROW within the quiescent centre is needed to maintain the stem cell status of surrounding cells. The position of the quiescent centre is determined by SCARECROW expression and by polar auxin movement. The importance of auxin transport for cell patterning within the root tip is exemplified by the orc mutant, which has a defective sterol methyl transferase. The normal basal distribution of the efflux carriers is altered in this mutant so that polar auxin transport is disrupted. Vegetative development Vegetative development is dependent on interactions at different levels, from the control of the cell cycle, meristem organization and activity, and cell patterning (differentiation), as well as developmental regulators and environmental signals. Jim Murray (University of Cambridge, UK) reported the development of a synchronous Arabidopsis cell culture system, which has been used to analyse gene expression patterns, particularly of cell-cycle-related genes. Cyclin D3 (CycD) expression is activated in mid-late G1 phase and responds to control by hormones and developmental regulators. Ectopic expression of this protein results in increased cell proliferation and reduced cell differentiation, suggesting that CycD’s are strong candidates as targets for genes promoting meristem activity and/or inhibiting cell differentiation. Thomas Laux (University of Freiburg, Germany) is searching for components of meristem organization downstream of WUS. Using novel genetic screens, several putative candidates have been identified, many of which appear to encode small, secreted peptides. Laux New frontiers in plant development: from genes to phenotype Peter Hedden, Michael J. Holdsworth, Gordon G. Simpson, Keith J. Edwards and John R. Lenton ‘ABI3 and FUS3…might primarily be regulators of vegetative development that were ‘co-opted’ to an embryo function.’ Apple blossom time at Long Ashton.