Inositol Signaling Interactors as Potential Regulators of Growth, Energy Sensing, and Biomass in Plants

Abstract

The sucrose nonfermenting-1-related kinase (SnRK1) is an important growth regulator and energy sensor in plants that is highly conserved among eukaryotes, and an ortholog of the human AMP kinase. Isoforms of SNRK1 overexpressed in plants result in delayed developmental transitions and increased biomass. Previously, we showed that native SnRK1.1 is degraded by the proteasome, and one member of the plant inositol signaling system, inositol 5-phosphatase 13 (5PTase13), protects SnRK1.1 from this degradation during low energy status in seedlings. In plants, inositol signaling is important for response and adaption to environmental stress. We report a new 5PTase13 interactor, P80, that contains WD40 repeats and interacts with the deubiquitination machinery. P80 loss-of-function seedlings have reduced root growth in low energy conditions that is reversed by adding sucrose, altered development and early senescence. Using transient expression in tobacco and immunoprecipitation, we show that P80 and another WD40 protein, WDR20, can be co-purified in a ternary complex with the deubiquitinase UBP3. Using recombinant proteins, we show that UBP3 has deubiquitinase activity in vitro and the WDR20-like protein stimulates this activity more than fourfold. Our findings indicate that a UPB3/P80/WDR20 deubiquitinase complex regulates growth and plant lifespan. We are testing an application to control plant growth and senescence through viral-induced gene silencing of P80 or SnRK1 in crop plants such as cotton.