Search PubMed⌕ Search

Biomedical subjects

Chiharu Ueguchi

Publications and source records attributed to Chiharu Ueguchi.

6 recordsLinked to original sources
PubMed2006

RNA interference of the Arabidopsis putative transcription factor TCP16 gene results in abortion of early pollen development.

Pollen development is a fundamental and essential biological process in seed plants. Pollen mother cells generated in anthers undergo meiosis, which gives rise to haploid microspores. The haploid cells then develop into mature pollen grains through two mitotic cell divisions. Although several sporophytic and gametophytic mutations affecting male gametogenesis have been identified and analyzed, little is known about the underlying molecular mechanism. In this study, we investigated the function of the TCP16 gene, which encodes a putative transcription factor. Expression analysis of the promoter::GUS fusion gene revealed that TCP16 transcription occurred predominantly in developing microspores. GUS expression began at the tetrad stage and markedly increased in an early unicellular stage. Transgenic plants harboring a TCP16 RNA interference (RNAi) construct generated equal amounts of normal and abnormal pollen grains. The abnormal pollen grains exhibited morphological abnormality and degeneration of genomic DNA. The defective phenotype of the RNAi plants was first detectable at the middle of the unicellular stage. Our results therefore suggest that TCP16, a putative transcription factor, plays a crucial role in early processes in pollen development.

Arabidopsis↗
PubMed2005

Cytokinin receptors are required for normal development of auxin-transporting vascular tissues in the hypocotyl but not in adventitious roots.

Plants alter the architecture of their root systems to adapt to the environment by modulating post-embryonic (lateral and adventitious) root formation and growth. To understand better the genetic basis of this regulation, we screened ethylmethane sulfonate-mutagenized lines of Arabidopsis thaliana for adventitious rooting mutants. One mutant showed retardation of the primary root growth, no production of lateral roots and enhanced formation of adventitious roots. Mapping and genetic complementation revealed that this mutant named wooden leg-3 (wol-3) was an allele of ARABIDOPSIS HISTIDINE KINASE 4 (AHK4), a locus known to encode a cytokinin receptor. Although the vascular system of the primary root and hypocotyl in the wol-3 mutant was aborted, that of the adventitious roots was normally developed. In the hypocotyl of the wol-3 mutant, auxin signals accumulated around the aborted vascular system. The application of auxin to primary roots induced lateral root formation in the wol-3 mutant. Transport of radiolabeled auxin from the top of the hypocotyl to the primary root was inhibited in wol-3. Although only a single amino acid alteration had occurred in AHK4, the root morphology in the wol-3 mutant was quite similar to that in the ahk2 ahk3 ahk4 triple mutant, which is a loss-of-function mutant of the three cytokinin receptors. This implies that the functional disturbance of AHK4 affects the function of the other receptors. Our results suggest that cytokinin receptors are necessary for the formation of auxin-transporting vascular tissues in the hypocotyl, but not in adventitious roots.

Alleles↗
PubMed2004

Histidine kinase homologs that act as cytokinin receptors possess overlapping functions in the regulation of shoot and root growth in Arabidopsis.

Cytokinins are plant hormones that may play essential and crucial roles in various aspects of plant growth and development. Although the functional significance of exogenous cytokinins as to the proliferation and differentiation of cells has been well documented, the biological roles of endogenous cytokinins have remained largely unknown. The recent discovery of the Arabidopsis Histidine Kinase 4 (AHK4)/CRE1/WOL cytokinin receptor in Arabidopsis thaliana strongly suggested that the cellular response to cytokinins involves a two-component signal transduction system. However, the lack of an apparent phenotype in the mutant, presumably because of genetic redundancy, prevented us from determining the in planta roles of the cytokinin receptor. To gain insight into the molecular functions of the three AHK genes AHK2, AHK3, and AHK4 in this study, we identified mutational alleles of the AHK2 and AHK3 genes, both of which encode sensor histidine kinases closely related to AHK4, and constructed a set of multiple ahk mutants. Application of exogenous cytokinins to the resultant strains revealed that both AHK2 and AHK3 function as positive regulators for cytokinin signaling similar to AHK4. The ahk2 ahk4 and ahk3 ahk4 double mutants and the ahk single mutants grew normally, whereas the ahk2 ahk3 double mutants exhibited a semidwarf phenotype as to shoots, such as a reduced leaf size and a reduced influorescence stem length. The growth and development of the ahk2 ahk3 ahk4 triple mutant were markedly inhibited in various tissues and organs, including the roots and leaves in the vegetative growth phase and the influorescence meristem in the reproductive phase. We showed that the inhibition of growth is associated with reduced meristematic activity of cells. Expression analysis involving AHK:beta-glucuronidase fusion genes suggested that the AHK genes are expressed ubiquitously in various tissues during postembryonic growth and development. Our results thus strongly suggest that the primary functions of AHK genes, and those of endogenous cytokinins, are triggering of the cell division and maintenance of the meristematic competence of cells to prevent subsequent differentiation until a sufficient number of cells has accumulated during organogenesis.

Arabidopsis↗
PubMed2003

The OsTB1 gene negatively regulates lateral branching in rice.

Although the shoot apical meristem (SAM) is ultimately responsible for post-embryonic development in higher plants, lateral meristems also play an important role in determining the final morphology of the above-ground part. Axillary buds developing at the axils of leaves produce additional shoot systems, lateral branches. The rice TB1 gene (OsTB1) was first identified based on its sequence similarity with maize TEOSINTE BRANCHED 1 (TB1), which is involved in lateral branching in maize. Both genes encode putative transcription factors carrying a basic helix-loop-helix type of DNA-binding motif, named the TCP domain. The genetic locus of OsTB1 suggested that OsTB1 is a real counterpart of maize TB1. Transgenic rice plants overexpressing OsTB1 exhibited markedly reduced lateral branching without the propagation of axillary buds being affected. We also demonstrated that a rice strain carrying a classical morphological marker mutation, fine culm 1 (fc1), contain the loss-of-function mutation of OsTB1 and exhibits enhanced lateral branching. Expression of OsTB1, as examined with a putative promoter-glucuronidase (GUS) gene fusion, was observed throughout the axillary bud, as well as the basal part of the shoot apical meristem, vascular tissues in the pith and the lamina joint. Taking these data together, we concluded that OsTB1 functions as a negative regulator for lateral branching in rice, presumably through expression in axillary buds.

Amino Acid Sequence↗