Investigating novel nutrient signaling mechanisms mediated by O-fucosylation and O-GlcNAcylation in plants.

Photosynthetic organisms provide food, energy, shelter, therapeutics, and a large diversity of vital biomolecules that sustain human life. The metabolic processes that produce these products are regulated by complex nutrient signaling pathways that are essential and highly conserved across kingdoms. Instead of being passively absorbed and fed into metabolic pathways, nutrient molecules such as nitrate, sugar, and their derivatives act as signals to regulate nutrient assimilation, metabolism, storage, as well as growth and developmental processes critical for plant productivity and nutritional values.

Two forms of vital sugar metabolites, uridine 5′-diphospho-N-acetylglucosamine (UDPGlcNAc) and guanosine 5′-diphospho-β-L-fucose (GDP-fucose), are used as donor substrates by SECRET AGENT (SEC) and SPINDLY (SPY) respectively. They modify the serine and threonine residues of many nucleocytoplasmic proteins in a reversible and dynamic manner. These two forms of essential post-translational modifications (PTM), known as O-linked-N-acetylglucosaminylation (O-GlcNAcylation) and O-linked fucosylation (O-fucosylation), are believed to represent evolutionarily conserved regulatory mechanisms that modulate protein functions and cellular responses according to energy and nutrient availability. Compromising O-GlcNAcylation and O-fucosylation causes lethality in both animals and plants.

Despite their essential functions, the study of O-GlcNAcylation and O-fucosylation (collectively termed O-glycosylation) in plants is still in its infancy. There is widespread speculation that O-GlcNAcylation and O-fucosylation play a role in metabolic signaling in plants, but there is no direct evidence to support this hypothesis. Our team aims to investigate how O-glycosylation modulates nutrient signaling using Arabidopsis as a model.

Preliminary results indicate that SPY and SEC play important roles in nitrate signaling and sugar signaling. Proteomic studies done by us show that key transcriptional and translational regulators in nitrate signaling and sugar signaling are O-GlcNAc and Ofucose modified. The proposed project will investigate if and how O-glycosylation of these candidates modulate nitrate and sugar signaling processes, using a combination of proteomics, transcriptomics, genetic, microscopic, and biochemical approaches. We will also screen for other direct and indirect SPY/SEC targets that modulate sugar signaling and perform functional studies. Importantly, we will investigate if and how Oglycosylation serves as a sugar sensor to mediate sugar sensing and growth regulation. Our proposed study will generate novel insight into plant metabolic signaling, providing theoretical basis for genetic engineering to boost crop yield and quality. Notably, OGlcNAcylation is closely related to many diseases and O-fucosylation modulates virulence of parasites. Knowledge gained on the conserved molecular functions of Oglycosylation could also be useful for advancing healthcare.