Identification, cloning and characterization of sis7 and sis10 sugar-insensitive mutants of Arabidopsis.
BACKGROUND
The levels of soluble sugars, such as glucose and sucrose, help regulate many plant metabolic, physiological and developmental processes. Genetic screens are helping identify some of the loci involved in plant sugar response and reveal extensive cross-talk between sugar and phytohormone response pathways.


RESULTS
A forward genetic screen was performed to identify mutants with increased resistance to the inhibitory effects of high levels of exogenous sugars on early Arabidopsis seedling development. The positional cloning and characterization of two of these sugar insensitive (sis) mutants, both of which are also involved in abscisic acid (ABA) biosynthesis or response, are reported. Plants carrying mutations in SIS7/NCED3/STO1 or SIS10/ABI3 are resistant to the inhibitory effects of high levels of exogenous Glc and Suc. Quantitative RT-PCR analyses indicate transcriptional upregulation of ABA biosynthesis genes by high concentrations of Glc in wild-type germinating seeds. Gene expression profiling revealed that a significant number of genes that are expressed at lower levels in germinating sis7-1/nced3-4/sto1-4 seeds than in wild-type seeds are implicated in auxin biosynthesis or transport, suggesting cross-talk between ABA and auxin response pathways. The degree of sugar insensitivity of different sis10/abi3 mutant seedlings shows a strong positive correlation with their level of ABA insensitivity during seed germination.


CONCLUSIONS
Mutations in the SIS7/NCED3/STO1 gene, which is primarily required for ABA biosynthesis under drought conditions, confer a sugar-insensitive phenotype, indicating that a constitutive role in ABA biosynthesis is not necessary to confer sugar insensitivity. Findings presented here clearly demonstrate that mutations in ABI3 can confer a sugar-insensitive phenotype and help explain previous, mixed reports on this topic by showing that ABA and sugar insensitivity exhibit a strong positive correlation in different abi3 mutants. Expression profiling revealed a potentially novel regulation of auxin metabolism and transport in an ABA deficient mutant, sis7-1/nced3-4/sto1-4.
Department of Plant Biology, University of Minnesota, 1500 Gortner Avenue, Saint Paul, MN 55108, USA. huan0277@umn.edu
Yadong
Y
Huang
Chun Yao
CY
Li
Kelly D
KD
Biddle
Susan I
SI
Gibson
D000040:Abscisic Acid / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D049308:Dioxygenases; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D005947:Glucose / Q000378:metabolism*; D007210:Indoleacetic Acids / Q000378:metabolism; D016254:Mutagenesis, Insertional; D009154:Mutation; D010105:Oxygenases / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D010937:Plant Growth Regulators / Q000378:metabolism; D010940:Plant Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D036226:Seedlings / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000235:genetics / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism*; D014158:Transcription, Genetic
D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D018744:DNA, Plant; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D010940:Plant Proteins; C036483:T-DNA; D013395:Sucrose; D000040:Abscisic Acid; D010105:Oxygenases; D049308:Dioxygenases; C109043:9-cis-epoxy-carotenoid dioxygenase; D005947:Glucose