SUGAR-INSENSITIVE3, a RING E3 Ligase, Is a New Player in Plant Sugar Response

Abstract

Sugars, such as sucrose and glucose, have been implicated in the regulation of diverse developmental events in plants and other organisms. We isolated an Arabidopsis (Arabidopsis thaliana) mutant, sugar-insensitive3 (sis3), that is resistant to the inhibitory effects of high concentrations of exogenous glucose and sucrose on early seedling development. In contrast to wildtype plants, sis3 mutants develop green, expanded cotyledons and true leaves when sown on medium containing high concentrations (e.g. 270 mM) of sucrose. Unlike some other sugar response mutants, sis3 exhibits wild-type responses to the inhibitory effects of abscisic acid and paclobutrazol, a gibberellic acid biosynthesis inhibitor, on seed germination. Map-based cloning revealed that SIS3 encodes a RING finger protein. Complementation of the sis3-2 mutant with a genomic SIS3 clone restored sugar sensitivity of sis3-2, confirming the identity of the SIS3 gene. Biochemical analyses demonstrated that SIS3 is functional in an in vitro ubiquitination assay and that the RING motif is sufficient for its activity. Our results indicate that SIS3 encodes a ubiquitin E3 ligase that is a positive regulator of sugar signaling during early seedling development.Almost all living organisms rely on the products of plant photosynthesis for sustenance, either directly or indirectly. Carbohydrates, the major photosynthates, provide both energy and carbon skeletons for fungi, plants, and animals. In addition, sugars, such as Suc and Glc, function as signaling molecules to regulate plant growth, development, gene expression, and metabolic processes. Sugar response pathways are integrated with other signaling pathways, such as those for light, phytohormones, stress, and nitrogen (Dijkwel et al

Arabidopsis Hexokinase-Like1 and Hexokinase1 Form a Critical Node in Mediating Plant Glucose and Ethylene Responses

“…This criterion is less well supported for HKL1 and HXK1 at present, largely due to the lack of studies in this area. However, the recent identification of SIS3, a ubiquitin E3 ligase, as a positive effector of sugar signaling could be important in this context (Huang et al, 2010). Nonetheless, since the outputs from a possible HXK1-HKL1 signaling node can have either positive or negative effects on plant growth responses, it is reasonable to presume that the cellular activation of either, or both, also involves contrasting control inputs.…”

Rice RING protein OsBBI1 with E3 ligase activity confers broad-spectrum resistance against Magnaporthe oryzae by modifying the cell wall defence

“…Therefore, we predicted that OsBBI1 belongs to the RING-H2 type of the RING family (Supplementary information, Figure S5). Of these, Arabidopsis BIG BROTHER, SDIR1, SIS3, RING1, NLA, SINAT5, and XBAT32, and rice EL5 and GW2 possess E3 ligase activity in vitro [38][39][40][41][42][43][44][45][46]. NLA, SIS3, SDIR1, and RING1 play roles in biotic and abiotic stress responses [40][41][42][43].…”

The circadian oscillator gene GIGANTEA mediates a long-term response of the Arabidopsis thaliana circadian clock to sucrose

“…Sugars, such as sucrose, are also important signaling molecules regulating growth, development, gene expression, and metabolism. Supplying high exogenous concentrations of sucrose (e.g., 300 mM, 10% wt/vol) severely inhibits early development of Arabidopsis seedlings, resulting in small white or purple cotyledons (16). Lower concentrations of sucrose (30-90 mM) do not inhibit shoot development although can interfere with a range of signal transduction pathways.…”