Presence of supercooling-facilitating (anti-ice nucleation) hydrolyzable tannins in deep supercooling xylem parenchyma cells in <Emphasis Type="Italic">Cercidiphyllum japonicum</Emphasis>

Xylem parenchyma cells (XPCs) in trees adapt to subzero temperatures by deep supercooling. Our previous study indicated the possibility of the presence of diverse kinds of supercooling-facilitating (SCF; anti-ice nucleation) substances in XPCs of katsura tree (Cercidiphyllum japonicum), all of which might have an important role in deep supercooling of XPCs. In the previous study, a few kinds of SCF flavonol glycosides were identified. Thus, in the present study, we tried to identify other kinds of SCF substances in XPCs of katsura tree. SCF substances were purified from xylem extracts by silica gel column chromatography and Sephadex LH-20 column chromatography. Then, four SCF substances isolated were identified by UV, mass and nuclear magnetic resonance analyses. The results showed that the four kinds of hydrolyzable gallotannins, 2,2′,5-tri-O-galloyl-α,β-d-hamamelose (trigalloyl Ham or kurigalin), 1,2,6-tri-O-galloyl-β-d-glucopyranoside (trigalloyl Glc), 1,2,3,6-tetra-O-galloyl-β-d-glucopyranoside (tetragalloyl Glc) and 1,2,3,4,6-penta-O-galloyl-β-d-glucopyranoside (pentagalloyl Glc), in XPCs exhibited supercooling capabilities in the range of 1.5–4.5°C, at a concentration of 1 mg mL⁻¹. These SCF substances, including flavonol glycosides and hydrolyzable gallotannins, may contribute to the supercooling in XPCs of katsura tree.     

CYP707A3, a major ABA 8'-hydroxylase involved in dehydration and rehydration response in Arabidopsis thaliana

Abscisic acid (ABA) catabolism is one of the determinants of endogenous ABA levels affecting numerous aspects of plant growth and abiotic stress responses. The major ABA catabolic pathway is triggered by ABA 8'-hydroxylation catalysed by the cytochrome P450 CYP707A family. Among four members of Arabidopsis CYP707As, the expression of CYP707A3 was most highly induced in response to both dehydration and subsequent rehydration. A T-DNA insertional cyp707a3-1 mutant contained higher ABA levels in turgid plants, which showed a reduced transpiration rate and hypersensitivity to exogenous ABA during early seedling growth. On dehydration, the cyp707a3-1 mutant accumulated a higher amount of stress-induced ABA than the wild type, an event that occurred relatively later and was coincident with slow drought induction of CYP707A3. The cyp707a3 mutant plants exhibited both exaggerated ABA-inducible gene expression and enhanced drought tolerance. Conversely, constitutive expression of CYP707A3 relieved growth retardation by ABA, increased transpiration, and a reduction of endogenous ABA in both turgid and dehydrated plants. Taken together, our results indicate that CYP707A3 plays an important role in determining threshold levels of ABA during dehydration and after rehydration.     

Solution structure of the kinase-associated domain 1 of mouse microtubule-associated protein/microtubule affinity-regulating kinase 3

Microtubule-associated protein/microtubule affinity-regulating kinases (MARKs)/PAR-1 are common regulators of cell polarity that are conserved from nematode to human. All of these kinases have a highly conserved C-terminal domain, which is termed the kinase-associated domain 1 (KA1), although its function is unknown. In this study, we determined the solution structure of the KA1 domain of mouse MARK3 by NMR spectroscopy. We found that approximately 50 additional residues preceding the previously defined KA1 domain are required for its proper folding. The newly defined KA1 domain adopts a compact alpha+beta structure with a betaalphabetabetabetabetaalpha topology. We also found a characteristic hydrophobic, concave surface surrounded by positively charged residues. This concave surface includes the highly conserved Glu-Leu-Lys-Leu motif at the C terminus, indicating that it is important for the function of the KA1 domain.     

Boron Nutrition of Tobacco BY-2 Cells. V. Oxidative Damage is the Major Cause of Cell Death Induced by Boron Deprivation

Boron (B) is an essential micronutrient for vascular plants.However, it remains unclear how B deficiency leads to variousmetabolic disorders and cell death. To understand this mechanism,we analyzed the physiological changes in suspension-culturedtobacco (Nicotiana tabacum) BY-2 cells upon B deprivation. When3-day-old cells were transferred to B-free medium, cell deathwas detectable as early as 12 h after treatment. The B-deprivedcells accumulated more reactive oxygen species and lipid peroxidesthan control cells, and showed a slight but significant decreasein the cellular ascorbate pool. Supplementing the media withlipophilic antioxidants effectively suppressed the death ofB-deprived cells, suggesting that the oxidative damage is theimmediate and major cause of cell death under B deficiency.Dead cells in B-free culture exhibited a characteristic morphologywith a shrunken cytoplasm, which is often seen in cells undergoingprogrammed cell death (PCD). However, they did not display otherhallmarks of PCD such as internucleosomal DNA fragmentation,decreased ascorbate peroxidase expression and protection fromdeath by cycloheximide. These results suggest that the deathof tobacco cells induced by B deprivation is not likely to bea typical PCD.     

A rice tryptophan deficient dwarf mutant, tdd1, contains a reduced level of indole acetic acid and develops abnormal flowers and organless embryos

Indole-3-acetic acid (IAA) plays a critical role in many aspects of plant growth and development; however, complete pathways of biosynthesis, localization and many aspects of functions of IAA in rice remain unclear. Here, we report the analysis of a rice tryptophan- (Trp-) and IAA-deficient mutant, tryptophan deficient dwarf1 ( tdd1 ) , which is embryonic lethal because of a failure to develop most organs during embryogenesis. Regenerated tdd1 plants showed pleiotropic phenotypes: dwarfing, narrow leaves, short roots and abnormal flowers. TDD1 encodes a protein homologous to anthranilate synthase β-subunit, which catalyses the first step of the Trp biosynthesis pathway and functions upstream of Trp-dependent IAA biosynthesis. TDD1-uidA and DR5-uidA expression overlapped at many sites in WT plants but was lacking in tdd1 , indicating that TDD1 is involved in auxin biosynthesis. Both Trp and IAA levels in flowers and embryos were much lower in tdd1 than in wild type (WT). Trp feeding completely rescued the mutant phenotypes and moderate expression of OsYUCCA1 , which encodes a key enzyme in Trp-dependent IAA biosynthesis, also rescued plant height and root length, indicating that the abnormal phenotypes of tdd1 are caused predominantly by Trp and IAA deficiency. In tdd1 embryos, the expression patterns of OSH1 and OsSCR , which mark the presumptive apical region and the L2 layer, respectively, are identical to those in WT, suggesting a possibility either that different IAA levels are required for basic pattern formation than for organ formation or that an orthologous gene compensates for TDD1 deficiency during pattern formation.     

The NMR solution structures of the five constituent cold-shock domains (CSD) of the human UNR (upstream of N-ras) protein

Upon cold shock, the amounts of most proteins dramatically decrease from normal levels, but those of cold shock proteins (CSPs) and proteins containing cold-shock domains (CSDs) greatly increase. Although their biological function is still not completely clear, cold-shock proteins might control translation via RNA chaperoning. Many cold-shock proteins contain the motifs (Y/F)GFI and (V/F)(V/F)H, which are known as ribonucleoprotein (RNP)-1 and RNP-2 motifs implicated in RNA/DNA binding. We determined the solution NMR structures of all five constituent CSDs of the human UNR (upstream of N-ras) protein. The spatial arrangements of the sidechains in the RNP-1 and RNP-2 motifs are mostly conserved; however, the conformations of the following residues in the first CSD are different: F43 and H45 (the first phenylalanine residue and the histidine residue in the putative binding site RNP-2) and Y30 (the first residue in the putative binding site RNP-1). F43 and H45 affect each other, and H45 is further influenced by C46. The altered binding site of the first CSD, and its putatively enhanced intrinsic stability, may provide an explanation for the observation that the first CSD has 20-fold higher RNA-binding activity than the fifth CSD. It also lends support to the hypothesis that the UNR protein arose by repeated duplication of a protein that originally contained just one CSD, and that the proto-UNR protein acquired cysteine C46 by mutation during evolution.