13th FASEB Plant Biology Conference- Mechanisms in Plant Development

The 13^th FASEB Plant Biology Conference was held from August 11- 16, 2013, in Saxtons River, Vermont, a modest but beautiful setting.  This was a special meeting, since it marked 25 years since the first FASEB Plant Molecular Biology conference- the theme changed to Plant Development in the mid ‘90’s. Around 160 attendees spent 5 days hearing the latest “developments” in plant development, and enjoying casual discussions in the swimming pond and the bar.

The meeting kicked off with an inspiring plenary talk by Prof. Liam Dolan (Oxford University).  Liam’s lab has been studying root hair patterning and other aspects of root development in Arabidopsis for many years, but in this talk he described new work that seeks to understand the evolutionary origin of root- like structures in plants. using a recently adopted liverwort model, Marchantia.

The following morning, the first session of the conference focused on the latest research on local signals. The speakers showed their work on plasmodesmata-dependent miRNA movement (Ykä Helariutta, University of Helsinki), endosome-dependent protein movement (Kimberly Gallagher, University of Pennsylvania) and recognition of Calcium signals in roots (Giles Oldroyd, John Innes Centre), sensing of CO₂ concentration in leaves (Cawas Engineer, UCSD) and cytokinin levels in secondary meristems (Yuval Eshed, Weizmann Institute). Furthermore, recent findings on the control of Arabidopsis embryo maturation and maize meristem size homeostasis (Michael Pautler, CHSL) were shared with the community.

In the polarity session, several different examples of cell- and tissue-level polarity were discussed. Jeff Long (Salk Institute) presented new work on the genetic specification and maintenance of apical-basal polarity via TOPLESS-dependent and –independent pathways in the Arabidopsis embryo, while Laurie Smith (UCSD) presented insights into the regulation of asymmetric cell divisions during stomatal development in maize. Remko Offringa (Leiden University) described how regulation of the protein kinase PINOID (PID) can influence the pattern of PIN polarity – and hence auxin transport within a tissue. Finally, Xana Rebocho (John Innes Centre) described the importance of the regulation of tissue polarity, and growth rates, for the morphogenesis of the Antirrhinum flower and the insights gained from modeling studies.

Shoot architecture of higher plants is determined by developmental events occurring at the growing tips.  Meristems are the site of organogenesis, giving rise to lateral organs, such as leaves and axillary branches, which themselves have meristematic properties.  A meristem contributes immobile cells to the formation of lateral organ primordia, and it is self-renewing.  A major outstanding question is precisely how cells dynamically accept cell fate at the meristem-incipient organ boundary during organ initiation.  An enthralling session devoted to boundaries featured studies from Rüdiger Simon (Heinrich-Heine University), Marcus Heisler (EMBL) and Klaus Theres (Max Planck Institute for Plant Breeding Research) that honed in on the genetic and molecular dissection of boundary specification and formation.

The meeting then moved on to considering long range signaling in plants. Leslie Sieburth (University of Utah) presented new findings on the bypass signal that coordinates the development of shoots and roots. David Braun (University of Missouri) discussed the Tie-Dyed (TDY) genes of maize; mutations in which show defects in phloem differentiation and sucrose trafficking. Micro-RNAs can also be transported long distances in the plant, and Tzyy-Jen Chiou (Academia Sinica, Taiwan) presented her research on the regulation of phosphate uptake and translocation, which involves miR399 acting as a systemic signal. In the last talk of the session, Catherine Rameau (INRA Versailles) discussed how Strigolactones and other long-range signals regulate shoot branching in pea.

Compared to Arabidopsis, many crops exhibit unique inflorescence structures requiring more coordinated transition from stem cell maintenance to floral organ formation. Inflorescence architecture is largely determined by the fate of meristems, population of stem cells under specific genetic control. In the session on switches, novel molecular regulators of this inflorescence development were presented in three major crops: tomato (Zachary Lippman, CSHL), rice (Junko Kyozuka, University of Tokyo), and corn (Paula McSteen, University of Missouri).

The signal integration session focused on the integration of molecular signals that coordinate complex environmental inputs and govern developmental outputs. The session highlighted an exciting array of developmental responses to the environment, from the phototracking of sunflowers to root patterning in heterogeneous soils. Jennifer Nemhauser (University of Washington) started out the session by introducing the hypocotyl as a model system for measuring the role of complex environmental input on developmental output. In the next talk, José Dinneny (Carnegie Institution) elucidated the role of heterogeneous water availability on lateral root patterning, a phenomenon referred to as “hydropatterning”. Stacey Harmer (UC Davis) was the next speaker. She emphasized the impact of the circadian clock on transcriptomic patterns. The Harmer lab harvested tissue every 4 hours for 2 days and found that half of all genes are differentially expressed in a time dependent manner. Harmer also introduced sunflower solar tracking as a model system to study circadian clock entrainment. The final speaker for the session was José Alonso (North Carolina State University), who presented a very clever mutant screen that was performed to fish out genes coordinating the relationship between auxin signaling and ethylene response.

Talks then turned to regulation of morphogenesis and shape. Olivier Hamant (Lyon) presented research on mechanical signals in plant morphogenesis, and the proposal that coupling between mechanical cues, microtubule (MT) alignment and PIN1 orientations plays a key role in morphogenesis and the generation of phyllotactic patterns. Uptal Nath (Indian Institute of Science) focuses on the molecular basis of polar leaf growth. Leaf growth is often allometric, where leaves experience polar growth – more growth at the base and progressively less towards the tip. His work has shown that the polarity of leaf growth can be diverse, and that this may be related to the expression of miR396. Next, Elliot Meyerowitz (Caltech) presented work describing how physical and chemical signals control morphogenesis at the shoot apical meristem. He suggested an approach in which all developmental biologists should consider the physical stresses acting in tissues and study morphogenesis as a whole using all parameters. Adrienne Roeder (Cornell) discussed how coordination of cell division and cell type control the morphogenesis of the Arabidopsis sepal, while Siobhan Braybrook presented data on how cell wall mechanics and pressure affect the overall shape of hypocotyl extension.

In the last session, participants returned to the Vermont Academy auditorium after an afternoon of outdoor activities. Refreshed by a game of volleyball, a jog through the woods, or a swim at the local pond, attendants were pleased to hear three fantastic stories outlining recent discoveries in developmental phenomena related to species evolution. Vincent Colot (Institut de Biologie de l’Ecole Normale Supérieure) presented his group’s recent work exploring the link between genome sequence, DNA methylation status, and plant phenotype. Claudia Köhler (Linnean Center of Plant Biology, Uppsala, Sweden) presented her group’s recent breakthroughs in understanding the mechanisms behind the ‘triploid block’ that causes the post-zygotic isolation of newly formed polyploid progeny. George Coupland (Max-Planck-Institute for Plant Breeding Research) finished off the session by presenting his group’s recent findings on the molecular mechanisms behind vernalization (induction by cold treatment) and age requirements for flowering in the genus Arabis.

The conference ended with a thoughtful overview by Scott Poethig (U. Penn). He reminded us of how our field has come full circle, from a situation where everyone studied a different plant, through a bottleneck where almost everyone worked on Arabidopsis or one or two other model systems, to a new era where genomics allows us to again use diverse species to tackle important problems in plant development.  He also reminded us how some concepts discussed at the meeting had been discussed much earlier, in particular reminding us of the seminal ideas of Paul Green in thinking about the role of mechanical forces in plant morphogenesis.  Overall it was a truly memorable meeting, and we look forward to the next FASEB Mechanisms in Plant Development meeting in 2015, which will be organized by Dominique Bergmann and Rudiger Simon.

This report was written by several of the students who attended the meeting. If you’re interested in finding out more, you can read their full report here (pdf)

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