A large deletion within intron 20 sequence of single-copy PolA1 gene as a useful marker for the speciation in Oryza AA-genome species.

Oryza AA-genome complex comprises five wild species, O. rufipogon, O. barthii, O. longistaminata, O. glumaepatula, and O. meridionalis. Evolutionary relationships among these five wild species have remained contentious and inconclusive. We found that intron 20 of PolA1, a single-copy nuclear gene, was short (S-type: 141-142 bp) in O. rufipogon, O. barthii, and O. glumaepatula, while long (L-type: ca. 1.5 kb) introns were apparent in O. longistaminata and O. meridionalis. Because Oryza species containing BB, CC, EE, FF, and GG genome showed L-type introns, the S-type intron was probably derived from the L-type intron by the deletion of a 1.4 kb fragment through intramolecular homologous recombination between two tandem TTTTGC repeats. Excluding the large deletion sequence, intron 20 sequence of O. barthii was identical to that of O. longistaminata. As more than 3,470 accessions of O. rufipogon and O. sativa also contained the same intron 20 sequence with O. longistaminata except for single T-nucleotide deletion, which was shared with O. glumaepatuala, the deletion of the T-nucleotide probably occurred in the L-type intron 20 of O. logistaminata. Deletions of a large 1.4 kb fragment and single T-nucleotide within the intron 20 of PolA1 gene were considered as useful DNA markers to study the evolutionary relationships among Oryza AA-genome species.

Growth increase of Arabidopsis by forced expression of rice 45S rRNA gene.

KEY MESSAGE: Forced expression of rice 45S rRNA gene conferred ca. 2-fold increase of above-ground growth in transgenic Arabidopsis . This growth increase was probably brought by cell proliferation, not by cell enlargement. Recent increase in carbon dioxide emissions is causing global climate change. The use of plant biomass as alternative energy source is one way to reduce these emissions. Therefore, reinforcement of plant biomass production is an urgent key issue to overcome both depletion of fossil energies and emission of carbon dioxide. Here, we created transgenic Arabidopsis with a 2-fold increase in above-ground growth by forced expression of the rice 45S rRNA gene using the maize ubiquitin promoter. Although the size of guard cells and ploidy of leaf-cells were similar between transgenic and control plants, numbers of stomata and pavement cells were much increased in the transgenic leaf. This data suggested that cell number, not cell expansion, was responsible for the growth increase, which might be brought by the forced expression of exogenous and full-length 45S rRNA gene. The expression level of rice 45S rRNA transcripts was very low, possibly triggering unknown machinery to enhance cell proliferation. Although microarray analysis showed enhanced expression of ethylene-responsive transcription factors, these factors might respond to ethylene induced by abiotic/biotic stresses or genomic incompatibility, which might be involved in the expression of species-specific internal transcribed spacer (ITS) sequences within rice 45S rRNA transcripts. Further analysis of the mechanism underlying the growth increase will contribute to understanding the regulation of the cell proliferation and the mechanism of hybrid vigor.

Expression of rice 45S rRNA promotes cell proliferation, leading to enhancement of growth in transgenic tobacco.

An increase in plant biomass production is desired to reduce emission of carbon dioxide emissions and arrest global climate change because it will provide a more source of energy production than fossil fuels. Recently, we found that forced expression of the rice 45S rRNA gene increased aboveground growth by ca. 2-fold in the transgenic Arabidopsis plants. Here, we created transgenic tobacco plants harboring the rice 45S rRNA driven by the maize ubiquitin promoter (UbiP::Os45SrRNA) or cauliflower mosaic virus 35S promoter (35SP::Os45SrRNA). In 35SP::Os45SrRNA and UbiP::Os45SrRNA transgenic tobacco plants, the leaf length and size were increased compared with control plants, leading to an increase of aboveground growth (dry weight) up to 2-fold at the early stage of seedling development. Conversely, leaf physiological traits, such as photosynthetic capacity, stomatal characteristics, and chlorophylls and RuBisCO protein contents, were similar between the transgenic and control plants. Flow cytometry analysis indicated that the transgenic plants had enhanced cell-proliferation especially in seedling root and leaf primordia. Microarray analysis revealed that genes encoding transcription factors, such as GIGANTEA-like, were more than 2-fold up-regulated in the transgenic plants. Although the mechanism underlying the increased growth has yet to be elucidated, this strategy could be used to increase biomass production in cereals, vegetables, and bio-energy plants.

Rapid identification of a narcotic plant Papaver bracteatum using flow cytometry.

In May 2011, numerous poppy plants closely resembling Papaver bracteatum Lindl., a type of narcotic plant that is illegal in Japan, were distributed directly from several large flower shops or through online shopping throughout Japan, including the Tokyo Metropolitan area. In order to better identify the narcotic plants, the relative nuclear DNA content at the vegetative stage was measured by flow cytometric (FCM) analysis in 3 closely-related species of the genus Papaver section Oxytona, namely P. orientale, P. pseudo-orientale, and P. bracteatum, based on the difference between the chromosome numbers of these species. The results showed that the nuclear DNA content differed between these 3 species, and that most of the commercially distributed plants examined in this study could be identified as P. bracteatum. The remaining plants were P. pseudo-orientale, a non-narcotic plant. In addition, the FCM results for the identification of P. bracteatum completely agreed with the results obtained by the morphological analysis, the inter-genic spacer sequence of rpl16-rpl14 (PS-ID sequence) of chloroplast DNA, and the presence of thebaine. These results clearly indicate the usefulness of FCM analysis for the identification of P. bracteatum plants, including when they are in their vegetative stage.