Cellular localization of the signaling components of Arabidopsis His-to-Asp phosphorelay.

In the higher plant, Arabidopsis thaliana, histidine-to-aspartate (His-to-Asp) phosphorelay signal transduction systems play crucial roles in propagation of environmental stimuli, including plant hormones. This plant has 11 sensor His-kinases, 5 histidine-containing phosphotransfer (HPt) factors (AHPs), and 20 response regulators (ARRs). To gain new insight into the functions of these phosphorelay components, their intracellular localization was examined with use of GFP-fusion proteins, constructed for certain representatives of HPt factors (AHP2) and type-A and type-B ARRs (ARR6/ARR7 and ARR10, respectively). The results showed that AHP2 is mainly located in the cytoplasmic space, while both the types of ARRs have an ability to enter preferentially into the nuclei, if not exclusively. Together with the results from an in vitro phosphorelay assay with AHP2 and ARRs, these results are discussed, in terms of a geneal framework of the Arabidopsis His-to-Asp phosphorelay network.     

Two types of putative nuclear factors that physically interact with histidine-containing phosphotransfer (Hpt) domains, signaling mediators in His-to-Asp phosphorelay, in Arabidopsis thaliana

The higher plant, Arabidopsis thaliana, has a large number of genes, each of which encodes a component of His-to-Asp phosphorelay signal transduction systems. One type of such signal transducers are the histidine-containing phosphotransmitters (termed AHPs), which presumably mediate His-to-Asp phosphorelay. Here we attempted to isolate a factor or factors that interact with AHP1, AHP2 and AHP3 by means of a yeast two-hybrid system. This allowed us to identify two types of nuclear-localizing proteins. They are the members of the type-B family of response regulators (specifically, ARR1, APP2 and ARR10), and a novel protein named TCP10. The binding of ARR1 to AHP2 was also confirmed by in vitro binding assays. Moreover, dephosphorylation of AHP2 was observed in a manner dependent on ARR in vitro. A subset of AHPs appeared to also interact with a protein that contains a TCP domain, a recently proposed basic helix-loop-helix motif. Because several factors carrying the TCP domain have been implicated in the regulation of growth and development in lateral organs, the binding of TCP10 to this subset of AHPs suggests a possible linkage between the His-to-Asp phosphorelay systems and plant growth regulation.     

l-Serine Production Improved by Analogue-resistant Mutants of a Methanol-utilizing Bacterium

In the higher plant, Arabidopsis thaliana, histidine-to-aspartate (His-to-Asp) phosphorelay signal transduction systems play crucial roles in propagation of environmental stimuli, including plant hormones. This plant has 11 sensor His-kinases, 5 histidine-containing phosphotransfer (HPt) factors (AHPs), and 20 response regulators (ARRs). To gain new insight into the functions of these phosphorelay components, their intracellular localization was examined with use of GFP-fusion proteins, constructed for certain representatives of HPt factors (AHP2) and type-A and type-B ARRs (ARR6/ARR7 and ARR10, respectively). The results showed that AHP2 is mainly located in the cytoplasmic space, while both the types of ARRs have an ability to enter preferentially into the nuclei, if not exclusively. Together with the results from an in vitro phosphorelay assay with AHP2 and ARRs, these results are discussed, in terms of a geneal framework of the Arabidopsis His-to-Asp phosphorelay network.     

Promoters of nuclear‐encoded respiratory chain Complex I genes from Arabidopsis thaliana contain a region essential for anther/pollen‐specific expression

Regulatory promoter regions responsible for the enhanced expression in anthers and pollen are defined in detail for three nuclear encoded mitochondrial Complex I (nCI) genes from Arabidopsis thaliana. Specific regulatory elements were found conserved in the 5′ upstream regions between three different genes encoding the 22 kDa (PSST), 55 kDa NADH binding (55 kDa) and 28 kDa (TYKY) subunits, respectively. Northern blot analysis and transgenic Arabidopsis plants carrying progressive deletions of the promoters fused to the β-glucuronidase (GUS) reporter gene by histochemical and fluorimetric methods showed that all three promoters drive enhanced expression of GUS specifically in anther tissues and in pollen grains. In at least two of these promoters the –200/–100 regions actively convey the pollen/anther-specific expression in gain of function experiments using CaMV 35S as a minimal promoter. These nCI promoters thus contain a specific regulatory region responding to the physiological demands on mitochondrial function during pollen maturation. Pollen-specific motifs located in these regions appear to consist of as little as seven nucleotides in the respective promoter context.