YUCCA2 (YUC2)-Mediated 3-Indoleacetic Acid (IAA) Biosynthesis Regulates Chloroplast RNA Editing by Relieving the Auxin Response Factor 1 (ARF1)-Dependent Inhibition of Editing Factors in Arabidopsis thaliana.

Although recent research progress on the abundant C-to-U RNA editing events in plant chloroplasts and mitochondria has uncovered many recognition factors and their molecular mechanisms, the intrinsic regulation of RNA editing within plants remains largely unknown. This study aimed to establish a regulatory relationship in Arabidopsis between the plant hormone auxin and chloroplast RNA editing. We first analyzed auxin response elements (AuxREs) present within promoters of chloroplast editing factors reported to date. We found that each has more than one AuxRE, suggesting a potential regulatory role of auxin in their expression. Further investigation unveiled that the depletion of auxin synthesis gene YUC2 reduces the expression of several editing factors. However, in yuc2 mutants, only the expression of CRR4, DYW1, ISE2, and ECD1 editing factors and the editing efficiency of their corresponding editing sites, ndhD-2 and rps14-149, were simultaneously suppressed. In addition, exogenous IAA and the overexpression of YUC2 enhanced the expression of these editing factors and the editing efficiency at the ndhD-2 and rps14-149 sites. These results suggested a direct effect of auxin upon the editing of the ndhD-2 and rps14-149 sites through the modulation of the expression of the editing factors. We further demonstrated that ARF1, a downstream transcription factor in the auxin-signaling pathway, could directly bind to and inactivate the promoters of CRR4, DYW1, and ISE2 in a dual-luciferase reporter system, thereby inhibiting their expression. Moreover, the overexpression of ARF1 in Arabidopsis significantly reduced the expression of the three editing factors and the editing efficiency at the ndhD-2 and rps14-149 sites. These data suggest that YUC2-mediated auxin biosynthesis governs the RNA-editing process through the ARF1-dependent signal transduction pathway.

The PPR protein RARE1-mediated editing of chloroplast accD transcripts is required for fatty acid biosynthesis and heat tolerance in Arabidopsis.

It has been reported that Arabidopsis chloroplast accD transcripts undergo RNA editing and that loss of accD-C794 RNA editing does not affect plant growth under normal conditions. To date, the exact biological role of accD-C794 editing has remained elusive. Here, we reveal an unexpected role for accD-C794 editing in response to heat stress. Loss of accD-C794 editing results in a yellow and dwarf phenotype with decreased chloroplast gene expression under heat stress, and artificial improvement of C794-edited accD gene expression enhances heat tolerance in Arabidopsis. These data suggest that accD-C794 editing confers heat tolerance in planta. We also found that treatment with the product of acetyl coenzyme A carboxylase (ACCase) could allay mutant phenotypic characteristics and showed that a mutation in the CAC3 gene for the α-subunit of ACCase was associated with dwarfism under heat stress. These observations indicate that defective accD-C794 editing may be intrinsic to reduced ACCase activity, thereby contributing to heat sensitivity. ACCase catalyzes the committed step of de novo fatty acid (FA) biosynthesis. FA content analysis revealed that unsaturated oleic (C18:1) and linoleic acids (C18:2) were low in the accD-C794 editing-defective mutant but high in the C794-edited accD-overexpressing plants compared with the wild type. Supplying exogenous C18:1 and C18:2 could rescue the mutant phenotype, suggesting that these FAs play an essential role in tolerance to heat stress. Transmission electron microscopy observations showed that heat stress seriously affected the membrane architecture in accD editing-defective mutants but not in accD-overexpressing plants. These results provide the first evidence that accD-C794 editing regulates FA biosynthesis for maintenance of membrane structural homeostasis under heat stress.

A mass spectrometry imaging approach on spatiotemporal distribution of multiple alkaloids in Gelsemium elegans.

Gelsemium elegans contains multiple alkaloids with pharmacological effects, thus researchers focus on the identification and application of alkaloids extracted from G. elegans. Regretfully, the spatiotemporal distribution of alkaloids in G. elegans is still unclear. In this study, the desorption electrospray ionization mass spectrometry imaging (DESI-MSI) was applied to simultaneously analyze the distribution of pharmacologically important alkaloids in different organ/tissue sections of G. elegans at different growth stages. Finally, 23 alkaloids were visualized in roots, stems and leaves at seedling stage and 19 alkaloids were observed at mature stage. In mature G. elegans, 16 alkaloids were distributed in vascular bundle region of mature roots, 15 alkaloids were mainly located in the pith region of mature stems and 2 alkaloids were enriched in epidermis region of mature stems. A total of 16 alkaloids were detected in leaf veins of mature leaves and 17 alkaloids were detected in shoots. Interestingly, diffusion and transfer of multiple alkaloids in tissues have been observed along with the development and maturation. This study comprehensively characterized the spatial metabolomics of G. elegans alkaloids, and the spatiotemporal distribution of alkaloid synthesis. In addition, the results also have reference value for the development and application of Gelsemium elegans and other medicinal plants.

An Arabidopsis mutant of inositol pentakisphosphate 2-kinase AtIPK1 displays reduced arsenate tolerance.

Arsenate [As(V)] toxicity is considered to be derived from similarities in the chemical properties of As(V) and phosphate (Pi). An Arabidopsis thaliana mutant of inositol pentakisphosphate 2-kinase (AtIPK1), atipk1-1, has previously exhibited lower level of phytate and higher level of Pi, relative to wild-type (WT). Here, atipk1-1 displayed hypersensitivity to As(V) stress and less As(V) uptake when compared to WT. Overexpression of AtIPK1 controlled by the CaMV 35S promoter partially rescued the As(V)-sensitive phenotype of atipk1-1. When compared to control Pi status, addition of Pi enhanced As(V) tolerance of both WT and atipk1-1 plants, while the arsenic concentration was less reduced in the latter genotype. Despite the higher Pi level in atipk1-1 than did WT plants, the mutant suffered more severe Pi starvation under Pi limitation stress, indicating that Pi homeostasis was altered in the mutant. Gene expression analysis of WT and atipk1-1 plants showed the diverse effect of As(V) stress on Pi starvation-dependent regulation of Pi-responsive genes. Our study suggested that a particular mechanism of As(V) toxicity existed in atipk1-1 mutant, and may offer new insights into the interactions between Pi homeostasis and As(V) detoxification in plants.

[The effects of lycopene on reactive oxygen species and anoxic damage in ischemia reperfusion injury in rats].

OBJECTIVE: To study the protective effects of lycopene (LP) on cerebral ischemia-reperfusion injury induced by focal cerebral ischemia and oxidative stress in rats. METHODS: 48 male Sprague-Dawley (SD) rats were randomly assigned into five groups: A (20 mg/kg LP), B (5 mg/kg LP), C (salad oil), D (salad oil) and E (basic feed control). A, B and C groups were given LP or salad oil orally for 15 d, then cerebral ischemia-reperfusion injury was established by middle cerebral artery occlusion (MCAO) and D group was used as fake surgery control. The contents of reactive oxygen species (ROS), nitric oxide (NO), lactic acid (LD) and the activities of nitric oxide synthetase (NOS) in cortex were measured at 24 h after reperfusion. The levels of HIF-1alpha mRNA and Bcl-2 mRNA in hippocampi were determined by using reverse transcription polymerase chain reaction (RT- PCR) technique. RESULTS: ROS levels of A, B, C, D and E groups were (114.23 +/- 18.91), (135.89 +/- 14.17), (171.37 +/- 25.76), (94.24 +/- 2.23) and (92.06 +/- 5.59) fluorescence intensity value/g protein, respectively (F = 9.038, P < 0.01); levels of NO were (6.60 +/- 0.77), (7.13 +/- 0.47), (8.38 +/- 0.80), (5.52 +/- 0.16) and (5.23 +/- 0.51) micromol/g protein respectively (F = 10.197, P < 0.01); levels of NOS were (0.817 +/- 0.016), (0.875 +/- 0.095), (1.030 +/- 0.101), (0.557 +/- 0.094) and (0.595 +/- 0.066) U/mg protein respectively (F = 14.555, P < 0.01); levels of LD were (0.381 +/- 0.069), (0.446 +/- 0.012), (0.576 +/- 0.059), (0.359 +/- 0.021) and (0.310 +/- 0.036) mmol/g protein respectively (F = 10.043, P < 0.01); HIF-1alpha mRNA expression levels in hippocampi were 0.865 +/- 0.274, 0.635 +/- 0.069, 0.491 +/- 0.067, 0.375 +/- 0.052 and 0.361 +/- 0.087, respectively (F = 40.520, P < 0.01); and Bcl-2 mRNA expression levels in hippocampi were 0.263 +/- 0.033, 0.330 +/- 0.028, 0.198 +/- 0.034, 0.304 +/- 0.039 and 0.236 +/- 0.025, respectively (F = 11.003, P < 0.01). CONCLUSION: The protective effects of LP may be related with its abilities of decreasing ROS and LD cumulation, alleviating inflammation and up-regulating the expression of protective genes.

An impedance immunosensor for the detection of the phytohormone abscisic acid.

The phytohormone abscisic acid (ABA) is the major player in mediating the adaptation of plants to stress. Previously developed phytohormonal biosensors usually employed indirect detection of the products of conjugated oxidase reactions. A label-free electrochemical impedance immunosensor for ABA detection was developed using an anti-ABA antibody adsorbed directly on a porous nanogold film. The film was produced electrochemically on a glassy carbon electrode in 0.008 mol/L hydrogen tetrachloroaurate solution containing 0.004 mol/L lead acetate with an applied potential of -0.5 V (versus Ag/AgCl) for 50 s. The anti-ABA antibody was immobilized onto the porous nanogold through electrostatic adsorption and covalent conjugation. Electrochemical impedance spectroscopy was used to characterize the successful construction of the porous nanogold film and the stepwise modification of the glassy carbon electrode. The concentration increase of the antigen brought about a decrease of the interfacial electron transfer, which also meant an increase of the impedance signal. The experimental parameters pH, antibody incubation time, and antibody concentration were optimized. The results showed significant linearity R = 0.9942, with the content of ABA in the range 0.5-5,000 ng/mL with a detection limit at about 0.1 ng/mL.

Photosynthesis of the flag leaf blade and its sheath in high-yielding hybrid rice 'Liangyoupeijiu'.

Using high-yielding hybrid rice 'Liangyoupeijiu' (LYP9) and hybrid rice 'Shanyou 63' (SY63) as the experimental materials and using (14)C radio-autography, the photosynthetic capacities and distribution of photosynthates in flag leaf blades and sheaths of LYP9 were studied. The results showed that net photosynthetic rates (Pn) of the flag leaf blades and sheaths of LYP9 were much higher than those of SY63; the light transmissivity rates (LT) measured at the medium height of the flag leaf sheaths and the penultimate leaf sheaths were also significantly higher than those of SY63. The incipient activities, total activities and activation percentages of Rubisco in the flag leaf blade and sheath of LYP9 were all higher than those of SY63. The photosynthate transport rate in the sheaths of LYP9, and the quantity of photosynthate transported to the spikes and transformed to economic yield of LYP9 were all higher than those of SY63. The photosynthates produced by the sheaths were mainly transported to spike to make a certain contribution (about 15%) to yield.

[High performance liquid chromatographic determination of internal hormones in inter-subspecific hybrid rice].

A simple, rapid and perfect extraction and determination method for the internal hormones (gibberellin acid (GA3), indole-3-acetic acid (IAA), zeatin (Z), abscisic acid (ABA)) in inter-subspecific hybrid rice with reversed-phase high performance liquid chromatography has been developed. The chromatographic conditions were as follows: a Waters C18 column (4.6 mm i.d. x 250 mm, 5 microns), an SPD-6AV detector set at 254 nm and the mobile phase was a mixture of methanol, water and acetic acid (45:54.2:0.8, volume ratio). The lower detection limits were 0.5 mg/L for GA3, 0.1 mg/L for IAA, 0.3 mg/L for Z and 0.03 mg/L for ABA.