Yoshimichi Okamura | Search PubMed

PubMed2003

Nitrate-independent expression of plant nitrate reductase in Lotus japonicus root nodules.

Nitrate-independent nitrate reductase (NR) activity is generally found in legume root nodules. Therefore, the effects of nitrate on plant NR activity and mRNA were investigated in the root nodules of Lotus japonicus (L. japonicus). Both NR activity and mRNA levels in roots and root nodules were up-regulated by the addition of nitrate. In the absence of nitrate, NR activity and mRNA were detected in root nodules but not in roots. Southern blotting analysis indicates that NR is encoded by a single gene in L. japonicus. No nitrate was detected in the root nodules or roots of plants grown in the absence of nitrate, while its accumulation was observed in plants supplied with exogenous nitrate. These results indicate that inducible-type NR can be expressed in root nodules in the absence of nitrate. The activation state of the nitrate-independent activity of NR was as high as that of NR activity induced by nitrate. NR mRNA expressed independently of nitrate in root nodules without nitrate was localized in the infected regions of the root nodules. Thus, the expression could be related to the specific structure and environment of root nodules.

Amino Acid Sequence↗

PubMed2002

Visualization by comprehensive microarray analysis of gene expression programs during transdifferentiation of mesophyll cells into xylem cells.

Plants have a unique transdifferentiation mechanism by which differentiated cells can initiate a new program of differentiation. We used a comprehensive analysis of gene expression in an in vitro zinnia (Zinnia elegans L.) culture model system to gather fundamental information about the gene regulation underlying the transdifferentiation of plant cells. In this model, photosynthetic mesophyll cells isolated from zinnia leaves transdifferentiate into xylem cells in a morphogenic process characterized by features such as secondary-wall formation and programmed cell death. More than 8,000 zinnia cDNA clones were isolated from an equalized cDNA library prepared from cultured cells transdifferentiating into xylem cells. Microarray analysis using these cDNAs revealed several types of unique gene regulation patterns, including: the transient expression of a set of genes during cell isolation, presumably induced by wounding; a rapid reduction in the expression of photosynthetic genes and the rapid induction of protein synthesis-associated genes during the first stage; the preferential induction of auxin-related genes during the subsequent stage; and the transient induction of genes closely associated with particular morphogenetic events, including cell-wall formation and degradation and programmed cell death during the final stage. This analysis also revealed a number of previously uncharacterized genes encoding proteins that function in signal transduction, such as protein kinases and transcription factors that are expressed in a stage-specific manner. These findings provide new clues to the molecular mechanisms of both plant transdifferentiation and wood formation.

Asteraceae↗