SIS8, a putative mitogen‐activated protein kinase kinase kinase, regulates sugar‐resistant seedling development in Arabidopsis

Abstract

SUMMARYSugar signaling pathways have been evolutionarily conserved among eukaryotes and are postulated to help regulate plant growth, development and responses to environmental cues. Forward genetic screens have identified sugar signaling or response mutants. Here we report the identification and characterization of Arabidopsis thaliana sugar insensitive8 (sis8) mutants, which display a sugar-resistant seedling development phenotype. Unlike many other sugar insensitive mutants, sis8 mutants exhibit wild-type responses to the inhibitory effects of abscisic acid and paclobutrazol (an inhibitor of gibberellin biosynthesis) on seed germination. Positional cloning of the SIS8 gene revealed that it encodes a putative mitogen-activated protein kinase kinase kinase (MAPKKK; At1g73660). SIS8 mRNA is expressed ubiquitously among Arabidopsis organs. A UDP-glucosyltransferase, UGT72E1 (At3g50740), was identified as an interacting partner of SIS8 based on a yeast two-hybrid screen and in planta bimolecular fluorescence complementation. Both SIS8-yellow fluorescent protein (YFP) and UGT72E1-YFP fusion proteins localize to the nucleus when transiently expressed in tobacco leaf cells. T-DNA insertions in At3g50740 cause a sugar-insensitive phenotype. These results indicate that SIS8, a putative MAPKKK, is a regulator of sugar response in Arabidopsis and interacts with a UDP-glucosyltransferase in the nucleus.

Plant Raf-like kinase integrates abscisic acid and hyperosmotic stress signaling upstream of SNF1-related protein kinase2

“…From studies using various other mutants, signal crosstalk among ABA, sugar, and ethylene in Arabidopsis has been proposed (39), although details of the mechanism have not been clarified. At1g73660, identified as the at6 locus that improves salt-stress tolerance (35), also has been identified as the gene responsible for sugar insensitive8 (sis8) showing sugar-resistant seedling growth (40,41). The loss-offunction mutant of At1g73660, however, exhibited a WT response to ABA, the gibberellic acid biosynthesis inhibitor paclobutrazol, and the ethylene precursor aminocyclopropane carboxylic acid in germination experiments (35,40), indicating that At1g73660 has a distinct function specific to salt and sugar.…”

Master regulators in plant glucose signaling networks

“…The application of super-resolution fluorescence microscopy (Doksani et al, 2013) will provide dynamic view of regulatory proteins in HXK1-mediated glucose signaling at single-molecule details in different subcellular compartments. It will be interesting to learn whether the E3 ligase, protein kinase and histone acetyltransferase identified through Arabidopsis sugar-response mutants may act downstream or independent of HXK1-mediated glucose signaling (Huang et al, 2010; Heisel et al, 2013: Huang et al, 2013). …”

AIK1, A Mitogen-Activated Protein Kinase, Modulates Abscisic Acid Responses through the MKK5-MPK6 Kinase Cascade

“…In plants, MAPK cascades have been shown to be involved in signaling pathways and activated by abiotic stresses such as cold, salt, touch, wounding, heat, UV, osmotic shock, and heavy metals (Tena et al, 2001;Zhang et al, 2006;Colcombet and Hirt, 2008;Liu, 2012). Recent studies have suggested that MAPK cascades are involved in several ABA responses, including antioxidant defenses, guard cell signaling, seed germination, and plant growth (Liu and Zhang, 2004;Xing et al, 2008;Jammes et al, 2009;Zong et al, 2009;Wang et al, 2010;Zhang et al, 2010;Huang et al, 2014;Danquah et al, 2015;Lee et al, 2015;Matsuoka et al, 2015). AtMKK1 and AtMPK6 were reported to link each other and mediate ABA-induced H 2 O 2 scavenger CAT1 (catalase 1) gene expression and H 2 O 2 production (Xing et al, 2008).…”