Characterization of a core module required for allocation decisions and adaptive responses in Arabidopsis.

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Adaptive responses can be broken down into four steps: sensing, signal integration, decision making processes and the execution of these decisions. While progress has been made in the field of Arabidopsis to understand signal perception and integration, little is known about decision making processes (here referred to as allocation decisions) and their execution. To address this, we have set up a “conflict of interest” forward genetic screen to identify major players in allocation decisions. Together with reverse genetic approaches and screens for interactors, we have uncovered a three-component module. The first component of the module is the shaggy-like kinase BIN2, which mediates signal integration. The second component is the conserved TRAPPII multi-subunit tethering complex that mediates decision-making processes at the trans-Golgi-network (TGN). The third component comprises a family of Rab GTPases that are posited to execute decisions downstream of the first two components. To dissect the molecular mechanisms of signal convergence at the BIN2-TRAPP-RAB module, we will use a combination of proteomics, biochemistry, genetics and high-resolution confocal microscopy. Our specific goals are to (1) elucidate the impact of brassinosteroid (BR)-induced post-translational modifications on the assembly and function of the TGN-associated TRAPPII tethering complexes, (2) characterize functional interactions between TRAPP complexes and Rab GTPases, and (3) assess how these instruct sorting and trafficking decisions. Our study will identify molecular mechanisms by which signaling at the TGN modulates sorting decisions that contribute to cell division, elongation, growth anisotropy and meristem function. Mechanistic insights gained here will lay a foundation for understanding plant adaptive growth and allocation decisions.