Regulation of proteasome assembly in auxin signaling

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

The hormone auxin is essential for a large number of cellular and developmental processes in plants. Auxin achieves many of its actions by inducing the expression of a large number of genes to carry out the necessary functions. The Aux/IAA protein family normally suppresses auxin-responsive gene expression. An intermediate step in auxin induced gene expression is the degradation of these proteins through a ubiquitination/ 26S proteasome regulated process that depends on the interaction of several multi-component protein complexes. The intervening steps for this auxin response pathway are far from being understood. Prior studies revealed the contribution of the Rac/Rop GTPases in relating the auxin stimulus to the intracellular machinery for Aux/IAA degradation. The auxin induced Aux/IAA protein degradation process involves impromptu assembly of the degradation apparatus in response to the signal and is regulated by the presence of the Aux/IAA substrates. Observations from cell culture and whole plant studies suggest that auxin and substrates together induce formation of protein complexes that appear as protein bodies in the nucleus (referred to as nuclear protein bodies, NPBs). Substrates and components of SCFTIR1, CSN and 26S proteasome are recruited into and co-exist in these protein complexes, although the dynamics of their recruitment into and exit out of the NPBs remain to be elucidated. These NPBs are biologically active since the level of substrates has been observed to decline from within these structures in response to auxin treatment. The main focus of the proposed research is to examine the biochemical property of these NPBs, their composition and activity, and to examine the presence of high molecular weight protein complexes involved in auxin signaling, or other more amenable signaling pathways that are known to be regulated by ubiquitination and 26S proteasome-mediated proteolysis under endogenous conditions. Broader Impact. Ubiquitination and 26S proteasome-regulated proteolysis underlies a large number of cellular and developmental processes in all eukaryotes, including cell division, growth and differentiation, and developmental pathways from embryogenesis to reproduction, senescence and programmed cell death. Malfunctioning of this system results in severe developmental problems, including debilitating neurological diseases and cancer in human and compromised ability to cope with stress and pathogens in plants. A regulated and dynamic process for assembly and disassembly of the molecular machinery to carry out degradation of selected proteins has been speculated. Information obtained will be important toward understanding auxin signaling, which in itself is a significant aspect of plant biology and represents a paradigm in plant cell signaling. The knowledge should also be applicable to other ubiquitination/26S proteasome regulated processes. The proposed research will provide training opportunities for postdocs, graduate students and undergraduates. The current group of undergraduates in the PIs laboratories includes four women and two men (including US citizens but natives of Afghanistan, Nepal and Ukraine); three of them are participating in the research related to the proposed studies. New students from a campus-wide NSF supported program for minority students (SPUR), will be recruited to start this summer.