Jasmonate induces biosynthesis of anthocyanin and proanthocyanidin in apple by mediating the JAZ1–TRB1–MYB9 complex

Jasmonate (JA) induces the biosynthesis of anthocyanin and proanthocyanidin. MdMYB9 is essential for modulating the accumulation of both anthocyanin and proanthocyanidin in apple, but the molecular mechanism for induction of anthocyanin and proanthocyanidin biosynthesis by JA is unclear. In this study, we discovered an apple telomere-binding protein (MdTRB1) to be the interacting protein of MdMYB9. A series of biological assays showed that MdTRB1 acted as a positive modulator of anthocyanin and proanthocyanidin accumulation, and is dependent on MdMYB9. MdTRB1 interacted with MdMYB9 and enhanced the activation activity of MdMYB9 to its downstream genes. In addition, we found that the JA signaling repressor MdJAZ1 interacted with MdTRB1 and interfered with the interaction between MdTRB1 and MdMYB9, therefore negatively modulating MdTRB1-promoted biosynthesis of anthocyanin and proanthocyanidin. These results show that the JAZ1–TRB1–MYB9 module dynamically modulates JA-mediated accumulation of anthocyanin and proanthocyanidin. Taken together, our data further expand the functional study of TRB1 and provide insights for further studies of the modulation of anthocyanin and proanthocyanidin biosynthesis by JA.     

Toxicity of Dopamine to Striatal Neurons In Vitro and Potentiation of Cell Death by a Mitochondrial Inhibitor

Abstract: Intrastriatal injections of the mitochondrial toxins malonate and 3-nitropropionic acid produce selective cell death similar to that seen in transient ischemia and Huntington's disease. The extent of cell death can be attenuated by pharmacological or surgical blockade of cortical glutamatergic input. It is not known, however, if dopamine contributes to toxicity caused by inhibition of mitochondrial function. Exposure of primary striatal cultures to dopamine resulted in dose-dependent death of neurons. Addition of medium supplement containing free radical scavengers and antioxidants decreased neuronal loss. At high concentrations of the amine, cell death was predominantly apoptotic. Methyl malonate was used to inhibit activity of the mitochondrial respiratory chain. Neither methyl malonate (50 µ M ) nor dopamine (2.5 µ M ) caused significant toxicity when added individually to cultures, whereas simultaneous addition of both compounds killed 60% of neurons. Addition of antioxidants and free radical scavengers to the incubation medium prevented this cell death. Dopamine (up to 250 µ M ) did not alter the ATP/ADP ratio after a 6-h incubation. Methyl malonate, at 500 µ M , reduced the ATP/ADP ratio by ∼30% after 6 h; this decrease was not augmented by coincubation with 25 µ M dopamine. Our results suggest that dopamine causes primarily apoptotic death of striatal neurons in culture without damaging cells by an early adverse action on oxidative phosphorylation. However, when combined with minimal inhibition of mitochondrial function, dopamine neurotoxicity is markedly enhanced.     

No interaction between methyl jasmonate and ozone in Pima cotton: growth and allocation respond independently to both

Ozone (O₃) is damaging to plants, inducing signalling pathways involving antagonism between jasmonates and ethylene. These pathways mediate O₃ responses, particularly to acute exposure, and their manipulation protected several species against acute and chronic O₃. We use chronic daily exposure of up to 163 ppb O₃, and twice weekly application of up to 320 µg plant^?1 methyl jasmonate (MeJA) to test two hypothesizes: 1) a low rate of MeJA does not affect growth but increases O₃ sensitivity; 2) a high rate inhibits growth but reduces O₃ sensitivity. Both hypotheses were rejected. Growth declined with increases in both MeJA and O₃. MeJA at 40 µg plant^?1 caused no direct effect, and at 160 µg plant^?1 reduced growth similarly at all O₃. Neither rate altered O₃ sensitivity. These additive responses are not consistent with protection by MeJA in this system. They may reflect inter‐specific differences in signalling, since O₃ concentrations used here exceeded some reported acute exposures. Alternatively, parallel responses to O₃ and MeJA may suggest that O₃‐induced jasmonates play a developmental role in chronic response but no protective role in the absence of lesions characteristic of acute exposure. MeJA appears useful as a probe of these mechanisms.     

Synthesis and radical-scavenging activity of C-methylated fisetin analogues

The radical-scavenging reaction of fisetin, a natural antioxidant found in strawberries, is known to proceed via hydrogen transfer to produce a fisetin radical intermediate. Thus, introduction of an electron-donating group into the fisetin molecule is expected to stabilize the radical, leading to enhanced radical-scavenging activity. In this study, fisetin derivatives in which methyl substituents were introduced at the ortho positions relative to the catechol hydroxyl groups were synthesized and their radical scavenging activities were evaluated and compared with that of the parent fisetin molecule. Among the methyl derivatives, 5′-methyl fisetin, in which the inherent planar structure of fisetin was retained, exhibited the strongest radical scavenging activity. Introduction of methyl substituents may be effective for the enhancement of various biological activities of antioxidants, particularly radical-scavenging activity.     

Volatile Methyl Esters of Medium Chain Length from the Bacterium Chitinophaga Fx7914

The analysis of the volatiles released by the novel bacterial isolate Chitinophaga Fx7914 revealed the presence of ca. 200 compounds including different methyl esters. These esters comprise monomethyl‐ and dimethyl‐branched, saturated, and unsaturated fatty acid methyl esters that have not been described as bacterial volatiles before. More than 30 esters of medium C‐chain length were identified, which belong to five main classes, methyl (S)‐2‐methylalkanoates (class A), methyl (S)‐2,(ω?1)‐dimethylalkanoates (class B), methyl 2,(ω?2)‐dimethylalkanoates (class C), methyl (E)‐2‐methylalk‐2‐enoates (class D), and methyl (E)‐2,(ω?1)‐dimethylalk‐2‐enoates (class E). The structures of the compounds were verified by GC/MS analysis and synthesis of the target compounds as methyl (S)‐2‐methyloctanoate ( 28 ), methyl (S)‐2,7‐dimethyloctanoate ((S)‐ 43 ), methyl 2,6‐dimethyloctanoate ( 49 ), methyl (E)‐2‐methylnon‐2‐enoate ( 20a ), and methyl (E)‐2,7‐dimethyloct‐2‐enoate ( 41a ). Furthermore, the natural saturated 2‐methyl‐branched methyl esters showed (S)‐configuration as confirmed by GC/MS experiments using chiral phases. Additionally, the biosynthetic pathway leading to the methyl esters was investigated by feeding experiments with labeled precursors. The Me group at C(2) is introduced by propanoate incorporation, while the methyl ester is formed from the respective carboxylic acid by a methyltransferase using S‐adenosylmethionine (SAM).     

Setting the stage for evolution of a new enzyme

The evolution of novel enzymes has fueled the diversification of life on earth for billions of years. Insights into events that set the stage for the evolution of a new enzyme can be obtained from ancestral reconstruction and laboratory evolution. Ancestral reconstruction can reveal the emergence of a promiscuous activity in a pre-existing protein and the impact of subsequent mutations that enhance a new activity. Laboratory evolution provides a more holistic view by revealing mutations elsewhere in the genome that indirectly enhance the level of a newly important enzymatic activity. This review will highlight recent studies that probe the early stages of the evolution of a new enzyme from these complementary points of view.     

Inhibitory effect of heavy water on mutability of chemically injured Escherichia coli cells

After E. coli cells (WP2 and WP2uvrA) were treated with chemical mutagens (methyl methanesulfonate, MMS; N-methyl-N-nitrosourea, MNU; 4-nitroquinoline 1-oxide, 4NQO) in 1/15 M phosphate buffer, the mutability of the treated cells plated on a D₂O-agar plate was compared with that plated on an ordinary H₂O-agar plate. The mutation frequency decreased more or less on the D₂O-agar plate. The D₂O-substitution effects, as termed by the relative mutation frequencies (MF_D2O/MF_H2O), are 0.92 for MMS, 0.29 for MNU, and 0.42 for 4NQO in WP2, and 0.68 for MMS, 0.49 for MNU, and 0.16 for 4NQO in WP2uvrA. The D₂O effect seemed to be partly related to the function of the uvrA gene-associated products. The pH dependence of mutability was discussed in connection with the D₂O-substitution effect.