Identification of genes encoding ALMT and MATE transporters as candidate aluminum tolerance genes from a typical acid soil plant, Psychotria rubra (Rubiaceae).

To understand how tropical plants have adapted to acid soils, we analyzed the transcriptome of seedlings of Psychotria rubra, a typical species found on acid soils. Using RNA-seq, we identified 22,798 genes, including several encoding proteins of the Al3+-activated malate transporter (ALMT) and multidrug and toxic compound extrusion (MATE) families. Molecular phylogenetic analysis of ALMTs and MATEs revealed the grouping of those from P. rubra, which may be useful to select targets for elucidating the molecular basis of P. rubra adaptation to acid soils in the future. The transcriptome datasets obtained in this study would help us to further understand the physiological and ecological aspects of soil adaptation of Psychotria species.

UDP-glycosyltransferases from the UGT73C subfamily in Barbarea vulgaris catalyze sapogenin 3-O-glucosylation in saponin-mediated insect resistance.

Triterpenoid saponins are bioactive metabolites that have evolved recurrently in plants, presumably for defense. Their biosynthesis is poorly understood, as is the relationship between bioactivity and structure. Barbarea vulgaris is the only crucifer known to produce saponins. Hederagenin and oleanolic acid cellobioside make some B. vulgaris plants resistant to important insect pests, while other, susceptible plants produce different saponins. Resistance could be caused by glucosylation of the sapogenins. We identified four family 1 glycosyltransferases (UGTs) that catalyze 3-O-glucosylation of the sapogenins oleanolic acid and hederagenin. Among these, UGT73C10 and UGT73C11 show highest activity, substrate specificity and regiospecificity, and are under positive selection, while UGT73C12 and UGT73C13 show lower substrate specificity and regiospecificity and are under purifying selection. The expression of UGT73C10 and UGT73C11 in different B. vulgaris organs correlates with saponin abundance. Monoglucosylated hederagenin and oleanolic acid were produced in vitro and tested for effects on P. nemorum. 3-O-ß-d-Glc hederagenin strongly deterred feeding, while 3-O-ß-d-Glc oleanolic acid only had a minor effect, showing that hydroxylation of C23 is important for resistance to this herbivore. The closest homolog in Arabidopsis thaliana, UGT73C5, only showed weak activity toward sapogenins. This indicates that UGT73C10 and UGT73C11 have neofunctionalized to specifically glucosylate sapogenins at the C3 position and demonstrates that C3 monoglucosylation activates resistance. As the UGTs from both the resistant and susceptible types of B. vulgaris glucosylate sapogenins and are not located in the known quantitative trait loci for resistance, the difference between the susceptible and resistant plant types is determined at an earlier stage in saponin biosynthesis.

Expression of the stress-related genes for glutathione S-transferase and ascorbate peroxidase in the most-glycinin-deficient soybean cultivar Tousan205 during seed maturation.

Global analysis of gene expression profiles in most-glycinin-deficient cultivar Tousan205, was performed by DNA microarray analysis. It was confirmed that Tousan205 lacks mRNA expression of three glycinin subunit precursor genes, G1 (A1aB1x), G2 (A2B1a), and G5 (A3B4), and lacks G4 (A5A4B3) protein. Most glycinin subunits were deficient in mature seeds of Tousan205. We compared the gene expression of Tousan205 with those of parent cultivar, Tamahomare, which was used for crossbreeding of Tousan205. As a result, Tousan205 exhibited higher expression of some seed maturation proteins, and stress-related genes such as glutathione S-transferase and ascorbate peroxidase. This result indicates the possibility that the decrease of main storage protein, glycinin causes stress in soybean.

Isolation stress for 30 days alters hepatic gene expression profiles, especially with reference to lipid metabolism in mice.

To elucidate the physiological responses to a social stressor, we exposed mice to an isolation stress and analyzed their hepatic gene expression profiles using a DNA microarray. Male BALB/c mice were exposed to isolation stress for 30 days, and then hepatic RNA was sampled and subjected to DNA microarray analysis. The isolation stress altered the expression of 420 genes (after considering the false discovery rate). Gene Ontology analysis of these differentially expressed genes indicated that the stress remarkably downregulated the lipid metabolism-related pathway through peroxisome proliferator-activated receptor-alpha, while the lipid biosynthesis pathway controlled by sterol regulatory element binding factor 1, Golgi vesicle transport, and secretory pathway-related genes were significantly upregulated. These results suggest that isolation for 30 days with a mild and consecutive social stress regulates the systems for lipid metabolism and also causes endoplasmic reticulum stress in mouse liver.

Defense-related signaling by interaction of arabinogalactan proteins and beta-glucosyl Yariv reagent inhibits gibberellin signaling in barley aleurone cells.

Arabinogalactan proteins (AGPs) are hydroxyproline-rich glycoproteins present at the plasma membrane and in extracellular spaces. A synthetic chemical, beta-glucosyl Yariv reagent (beta-GlcY), binds specifically to AGPs. We previously reported that gibberellin signaling is specifically inhibited by beta-GlcY treatment in barley aleurone protoplasts. In the present study, we found that beta-GlcY also inhibited gibberellin-induced programmed cell death (PCD) in aleurone cells. We examined the universality and specificity of the inhibitory effect of beta-GlcY on gibberellin signaling using microarray analysis and found that beta-GlcY was largely effective in repressing gibberellin-induced gene expression. In addition, >100 genes were up-regulated by beta-GlcY in a gibberellin-independent manner, and many of these were categorized as defense-related genes. Defense signaling triggered by several defense system inducers such as jasmonic acid and a chitin elicitor could inhibit gibberellin-inducible events such as alpha-amylase secretion, PCD and expression of some gibberellin-inducible genes in aleurone cells. Furthermore, beta-GlcY repressed the gibberellin-inducible Ca2+-ATPase gene which is important for gibberellin-dependent gene expression, and induced known repressors of gibberellin signaling, two WRKY genes and a NAK kinase gene. These effects of beta-GlcY were also phenocopied by the chitin elicitor and/or jasmonic acid. These results indicate that gibberellin signaling is under the regulation of defense-related signaling in aleurone cells. It is also probable that AGPs are involved in the perception of stimuli causing defense responses.

Mitochondrial small heat-shock protein enhances thermotolerance in tobacco plants.

To clarify the role of mitochondrial small heat-shock protein (MT-sHSP) in the heat-shock response, we introduced the tomato (Lycopersicon esculentum) MT-sHSP gene under the control of the 35S promoter into tobacco (Nicotiana tabacum), and examined the thermotolerance of the transformed plants. Irrespective of the orientation, sense or antisense, of the gene, the transgenic plants exhibited a normal morphology and growth rate in the vegetative growth stage. When 4-week-old seedlings were exposed to sudden heat stress, the sense plants which overexpress the MT-sHSP gene exhibited thermotolerance, whereas the antisense plants in which the expression of the gene is suppressed exhibited susceptibility.