Mutation of Arabidopsis Copper-Containing Amine Oxidase Gene AtCuAOδ Alters Polyamines, Reduces Gibberellin Content and Affects Development

Gibberellin 2-oxidase 1(CsGA2ox1) involved gibberellin biosynthesis regulates sprouting time in camellia sinensis

BACKGROUND

Tea is an important cash crop and buds are its main product. To elucidate the molecular mechanism of the sprouting time of tea plants, 'Yuchunzao', which was an early sprouting tea cultivar, was studied. 'Echa 1', sprout one week later than 'Yuchunzao' in spring, was used as the control.

RESULTS

A total of 26 hormonal compounds and its derivatives in tea plants were qualified by using Ultra Performance Liquid Chromatography-Tandem mass spectrometry (UPLC-MS/MS). The result showed that GA20, GA3 and ICA were significantly different in 'Yuchunzao' than in 'Echa 1', with GA20 and GA3 up-regulated and ICA down-regulated. Based on the Illumina platform, transcriptome analysis revealed a total of 5,395 differentially expressed genes (DEGs). A diterpenoid biosynthesis related gene, gibberellin 2-oxidase 1 (CsGA2ox1), was downregulated in 'Yuchunzao' compared to 'Echa 1'. CsGA2ox1 regulate the transformation of GA different forms in plants. The relative expression of CsGA2ox1 showed an adverse trend with the content of GA20 and GA3. Our results suggest that down regulation of CsGA2ox1 resulted in the accumulation of GA3 and GA20, and then promoted sprout of 'Yuchunzao'.

CONCLUSION

This study provides theoretical basis of tea plants sprout and guides the tea breeding in practice.

CsCuAOs and CsAMADH1 Are Required for Putrescine-Derived γ-Aminobutyric Acid Accumulation in Tea

Polyamines are a potential source of γ-aminobutyric acid (GABA) in plants under abiotic stress. However, studies on GABA enrichment in tea mostly focus on the GABA shunt, while the correlation between polyamine degradation and GABA formation in tea is largely unknown. In this study, tea plants responded to exogenous putrescine, resulting in a significant increase in GABA content, while the glutamate level did not change. At the same time, five copper-containing amine oxidase (CuAO) and eight aminoaldehyde dehydrogenase (AMADH) genes involved in the putrescine-derived GABA pathway were identified from the Tea Plant Information Archive. Expression analysis indicated that CsCuAO1, CsCuAO3 as well as CsAMADH1 were induced to play an important function in response to exogenous putrescine. Thus, the three genes were cloned and the catalytic efficiency of soluble recombinant proteins was determined. CsCuAOs and CsAMADH1 exhibited indispensable functions in the GABA production from putrescine in vitro. Subcellular localization assays indicated that CsAMADH1 was localized in plastid, while both CsCuAO1 and CsCuAO3 were localized in peroxisome. In addition, the synergistic effects of CsCuAOs and CsAMADH1 were investigated by a transient co-expression system in Nicotiana benthamiana. Our data suggest that these three genes regulate the accumulation of GABA in tea by participating in the polyamine degradation pathway and improve the content of GABA in tea to a certain extent. The results will greatly contribute to the production of GABA tea.

Modulation of polyamine metabolism in Arabidopsis thaliana by salicylic acid

Polyamines (PAs) play important roles in plant defense against pathogens, but the regulation of PA metabolism by hormone-mediated defense signaling pathways has not been studied in depth. In this study, the modulation of PA metabolism by salicylic acid (SA) was analyzed in Arabidopsis by combining the exogenous application of this hormone with PA biosynthesis and SA synthesis/signaling mutants. SA induced notable modifications of PA metabolism, mainly consisting in putrescine (Put) accumulation both in whole-plant extracts and apoplastic fluids. Put was accumulated at the expense of increased biosynthesis by ARGININE DECARBOXYLASE 2 and decreased oxidation by copper amine oxidase. Enhancement of Put levels by SA was independent of the regulatory protein NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1) and the signaling kinases MKK4 and MPK3, but depended on MPK6. However, plant infection by Pseudomonas syringae pv. tomato DC3000 elicited Put accumulation in an SA-dependent way. The present study demonstrates a clear connection between SA signaling and plant PA metabolism in Arabidopsis and contributes to understanding the mechanisms by which SA modulates PA levels during plant-pathogen interactions.

Plant Copper Amine Oxidases: Key Players in Hormone Signaling Leading to Stress-Induced Phenotypic Plasticity

Polyamines are ubiquitous, low-molecular-weight aliphatic compounds, present in living organisms and essential for cell growth and differentiation. Copper amine oxidases (CuAOs) oxidize polyamines to aminoaldehydes releasing ammonium and hydrogen peroxide, which participates in the complex network of reactive oxygen species acting as signaling molecules involved in responses to biotic and abiotic stresses. CuAOs have been identified and characterized in different plant species, but the most extensive study on a CuAO gene family has been carried out in Arabidopsis thaliana. Growing attention has been devoted in the last years to the investigation of the CuAO expression pattern during development and in response to an array of stress and stress-related hormones, events in which recent studies have highlighted CuAOs to play a key role by modulation of a multilevel phenotypic plasticity expression. In this review, the attention will be focused on the involvement of different AtCuAOs in the IAA/JA/ABA signal transduction pathways which mediate stress-induced phenotypic plasticity events.

Physiological and Proteomic Analysis of Different Molecular Mechanisms of Sugar Beet Response to Acidic and Alkaline pH Environment

Soil pH is a major constraint to crop plant growth and production. Limited data are available on sugar beet growth status under different pH conditions. In this study, we analyzed the growth status and phenotype of sugar beet under pH 5, pH 7.5, and pH 9.5. It was found that the growth of sugar beet was best at pH 9.5 and worst at pH 5. The activities of superoxide dismutase (SOD) and peroxidase (POD) in leaves and roots increased as pH decreased from 9.5 to 5. Moreover, compared with pH 9.5, the levels of soluble sugar and proline in leaves increased significantly at pH 5. To explore the mechanisms of sugar beet response to different soil pH environments, we hypothesized that proteins play an important role in plant response to acidic and alkaline pH environment. Thus, the proteome changes in sugar beet modulated by pH treatment were accessed by TMT-based quantitative proteomic analysis. A total of three groups of differentially expressed proteins (DEPs) (pH 5 vs. pH 7.5, pH 9.5 vs. pH7.5 and pH 5 vs. pH 9.5) were identified in the leaves and roots of sugar beet. Several key proteins related to the difference of sugar beet response to acid (pH 5) and alkaline (pH 9.5) and involved in response to acid stress were detected and discussed. Moreover, based on proteomics results, QRT-PCR analysis confirmed that expression levels of three N transporters (NTR1, NRT2.1, and NRT2.5) in roots were relatively high under alkaline conditions (pH 9.5) compared with pH 5 or pH 7.5. The total nitrogen content of pH 9.5 in sugar beet was significantly higher than that of pH 7.5 and pH 5. These studies increase our understanding of the molecular mechanism of sugar beet response to different pH environments.