Osmotic Stress Leads to Significant Changes in Rice Root Metabolic Profiles between Tolerant and Sensitive Genotypes.

To breed osmotic stress-tolerant rice, the mechanisms involved in maintaining root growth under osmotic stress is important to elucidate. In this study, two rice (Oryza sativa L.) cultivars, IR 58 (stress-tolerant cultivar) and Basilanon (stress-sensitive cultivar), were used. After 1, 3, and 7 days of -0.42 MPa osmotic stress treatment induced by polyethylene glycol (PEG) 6000, root metabolomes were analyzed, yielding 276 detected compounds. Among 276 metabolites, 102 metabolites increased with the duration of the stress treatment in IR 58 roots, and only nine metabolites decreased. In contrast, 51 metabolites increased, and 45 metabolites decreased in Basilanon roots. Principal component analysis (PCA) scores clearly indicated differences between the cultivars and the treatments. Pathway analysis showed that the metabolites exhibiting stress-induced increases in IR 58 were those involved in sugar metabolism (such as sucrose 6'-phosphate, glucose 1-phosphate), polyamine and phenylpropanoid metabolisms (such as spermine, spermidine, gamma-aminobutyric acid (GABA)), and glutathione metabolism (such as glutathione, cysteine, cadaverine). IR 58 roots showed an increase in the most proteinogenic amino acids such as proline, serine, glutamine and asparagine. It was also maintained or increased the tricarboxylic acid (TCA) cycle intermediates (citric acid, cis-Aconitic acid, isocitric acid, fumaric acid, malic acid) under osmotic stress compared with that under control. Therefore, IR 58 actively synthesized various metabolites, and the increase in these metabolites contributed to the maintenance of important biological functions such as energy production and antioxidant defense to promote root development under osmotic stress.

Ectopic localization of auxin and cytokinin in tobacco seedlings by the plant-oncogenic AK-6b gene of Agrobacterium tumefaciens AKE10.

The oncogenic 6b gene of Agrobacterium tumefaciens induces a number of morphological and metabolic alterations in plants. Although molecular functions associated with the 6b genes have been proposed, including auxin transport, sugar transport, transcriptional regulation, and miRNA metabolism, so far an unequivocal conclusion has not been obtained. We investigated the association between auxin accumulation and tumor development of the tobacco seedlings expressing the AK-6b gene under the control of the dexamethasone-inducible promoter. Indole-3-acetic acid (IAA) localization was examined by immunochemical staining with monoclonal antibody against IAA and by histochemical analysis using the IAA-specific induced construct, DR5::GUS (ß-glucuronidase). Both procedures indicated that IAA preferentially accumulated in the tumorous protrusions as well as in newly developing vascular bundles in the tumors. Furthermore, true leaves also showed abaxial IAA localization, leading to altered leaves in which the adaxial and abaxial identities were no longer evident. Co-localization of cytokinin and auxin in the abaxial tumors was verified by immunochemical staining with an antibody against cytokinin. Treatment of AK-6b-seedlings with N-1-naphthylphthalamic acid, an inhibitor of polar auxin transport, promoted the morphological severity of phenotypes, whereas 1-naphthoxyacetic acid, a specific auxin influx carrier inhibitor, induced tumor regression on cotyledons and new tumorous proliferations on hypocotyls. Prominent accumulation of both auxin and cytokinin was observed in both regressed and newly developing tumors. We suggest from these results that modulation of auxin/cytokinin localization as a result of AK-6b gene expression is responsible for the tumorous proliferation.

Relationships between homeoprotein EGAM1C and the expression of the placental prolactin gene family in mouse placentae and trophoblast stem cells.

The mouse Crxos gene encodes three structurally related homeoproteins, EGAM1, EGAM1N, and EGAM1C, as transcription and splicing variants. Recently, we identified the functions of EGAM1 and EGAM1N in the regulation of differentiation in mouse embryonic stem cells. However, the function of EGAM1C remains unknown. To explore the additional roles of these proteins, the ontogenic expression of the respective mRNAs in post implantation mouse embryos and extraembryonic tissues, particularly from embryonic day (E) 10.5 to E18.5, was analyzed. The expression of Egam1n mRNA was specifically detected in embryos throughout this period, whereas that of Egam1 was undetectable in any of the tissues examined. However, in the placenta, Egam1c mRNA and its encoded protein were detected after E16.5, and these expression levels increased by E18.5 immediately before partum. Quantitative RT-PCR and in situ hybridization analyses in placentae revealed that the spatial and temporal expression patterns of the Egam1c mRNA were related to some extent with those of Prl3a1 and Prl5a1 and partially overlapped that of Prl3b1, which are members of the placental prolactin (PRL) gene family. When EGAM1C was overexpressed moderately in mouse trophoblast stem cells as a model for undifferentiated and differentiating placental cell types, the expression levels of endogenous Prl3b1 and Prl5a1 were enhanced under both undifferentiated and differentiating culture conditions. These results indicated that EGAM1C may play a role in the expression of members of the placental PRL gene family, such as Prl3b1 and Prl5a1.

Identification of sorbitol transporters expressed in the phloem of apple source leaves.

Sorbitol is a major photosynthetic product and a major phloem-translocated component in Rosaceae (e.g. apple, pear, peach, and cherry). We isolated the three cDNAs, MdSOT3, MdSOT4, and MdSOT5 from apple (Malus domestica) source leaves, which are homologous to plant polyol transporters. Yeasts transformed with the MdSOTs took up sorbitol significantly. MdSOT3- and MdSOT5-dependent sorbitol uptake was strongly inhibited by xylitol and myo-inositol, but not or only weakly by mannitol and dulcitol. Apparent K(m) values of MdSOT3 and MdSOT5 for sorbitol were estimated to be 0.71 mM and 3.2 mM, respectively. The protonophore, carbonyl cyanide m-chlorophenylhydrazone (CCCP), strongly inhibited the sorbitol transport. MdSOT3 was expressed specifically in source leaves, whereas MdSOT4 and MdSOT5 were expressed in source leaves and also in some sink organs. MdSOT4 and MdSOT5 expressions were highest in flowers. Fruits showed no or only weak MdSOT expression. Although MdSOT4 and MdSOT5 were also expressed in immature leaves, MdSOT expressions increased with leaf maturation. In addition, in situ hybridization revealed that all MdSOTs were expressed to high levels in phloem of minor veins in source leaves. These results suggest that these MdSOTs are involved in sorbitol loading in Rosaceae.

Characterization of rice functional monosaccharide transporter, OsMST5.

cDNA of a monosaccharide transporter in rice, OsMST5 (Oryza sativa monosaccharide transporter 5) was cloned and its sugar transport activity was characterized by heterologous expression analysis. The amino acid sequence and topology were similar to the sequences and topology of other plant monosaccharide transporters. Yeast cells co-expressed with OsMST5 cDNA transported some monosaccharide substrates. The transport rate increased when ethanol as an electron donor was added, so the transporter was an energy-dependent active one. Most of the OsMST5 was expressed in panicles before pollination, indicating that it is associated with pollen development in rice.