Carbohydrates have signaling functions in regulating gene expression, metabolic
pathways and developmental processes. Eukaryotic organisms have evolved conserved
and novel mechanisms for sensing and responding to sugars. Plant sugar response
pathways are complex and exhibit cross-talk with other response pathways.
Sugar responses and signaling pathways have been studied via physiological,
biochemical and genetic approaches. Genetic screens have identified sugar response
mutants with altered seedling growth phenotypes. The Gibson lab has isolated an array of
sugar insensitive (sis) mutants by screening mutagenized Arabidopsis seeds on high
concentrations of sugars. The identification and characterization of three of the SIS genes,
SIS7, SIS3 and SIS8, are presented here.
SIS7 is allelic to NCED3/STO1, an abscisic acid (ABA) biosynthetic gene, which
is involved in drought and salt stress responses. Lateral root (LR) development of sis7
mutants is resistant to the inhibitory effects of osmotica. Transcriptomic analysis revealed
that a set of auxin-related genes are expressed at lower levels in sis7 seeds than in wildtype
seeds when incubated with glucose, suggesting that these genes may be involved in
controlling LR development by both ABA and auxin.
SIS3 encodes a RING finger protein that functions as an E3 ligase in in vitro
ubiquitination assays. The sis3 seeds display wild-type germination responses to ABA
and GA. However, the root growth of sis3 mutants has slightly reduced sensitivity to
The sis8 mutants have decreased sensitivity to high sugars and hyperosmolarity.
Positional cloning of sis8 revealed that the mutation is in a putative mitogen-activated
protein kinase kinase kinase gene. Seed germination assays indicate that sis8 mutants
have wild-type sensitivity to ABA and GA, whereas overexpression of SIS8 causes slight
hypersensitive responses. Potential interaction partners of SIS8 have been identified via
yeast two-hybrid screening. A T-DNA insertion in the gene encoding one potential SIS8-
interacting protein, UGT72E1, causes a sis phenotype.
Further studies of the SIS3 and SIS8 genes will provide more insight into the
mechanisms of sugar signaling in plants.
University of Minnesota Ph.D. disseration. October 2008. Major: Plant biological sciences. Advisor: Dr. Susan I. Gibson. 1 computer file (PDF); ix, 208 pages.
Identification and characterization of three Arabidopsis sugar insensitive genes.
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