Hydrogen Peroxide Accumulation Regulated by LjRbohD Modulates Nodulation of Lotus japonicus Under Blue Light

In many legumes, roots that are exposed to blue light do not form nodules, and blue light induces the biosynthesis of hydrogen peroxide (H2O2). The mechanism of blue light restraining nodulation is poorly understood. Whether H2O2 induced by blue light inhibits nodulation needs to be further studied. In this work, blue light could promote the production of H2O2, activate the expression of LjRbohD and LjRbohE, while inhibit the expression of LjRbohB. After applying exogenous H2O2 and diphenyleneiodonium chloride (DPI), the results show H2O2 induced by blue light represses the nodulation of MG20. The accumulated H2O2 may be generated by LjRbohD, which supported by Q-PCR. Cryptochrome 1A, a blue light photoreceptor, is high expression under blue light. However, there seems to be no direct relationship between LjRbohD and LjCry1A. On the contrary, LjRbohB, a positive governor in the regulation of nitrogen fixation activity in L. japonicus, may be negatively regulated by LjCry1A according to the hairy roots transformation results. Therefore, the mechanisms of regulating the nodulation in L. japonicus by LjRbohB and LjRbohD are quite different under blue light. Keywords: Louts japonicus, accumulated H2O2, blue light, nodulation, LjRbohs.

Loss of The Phloem-Expressed Sugar Transporter VST1 Reduces Aphid Performance In Watermelon

Aphids can damage plants through sugar withdrawal by hijacking sugar metabolism and transport genes to increase their sugar sucking ability. Blocking plant diseases and pest access to nutrients has emerged as an exciting strategy for improving disease and insect resistance in plants. Our previous work identified a shift in the localization of the vacuolar sugar transporter (VST1) that contributes to sucrose (Suc) and glucose (Glc) unloading in the phloem of sweet watermelons. In this study, the potential role of VST1 in the response to aphid infestation was investigated. Loss of VST1 function adversely impacted aphid settling and honeydew production. The vst1 mutant displayed less aphid-induced hydrogen peroxide accumulation and cell death than wild-type (WT) plants. Additionally, the expression of the VST1 gene was induced by aphids. The mutation of VST1 reduced Suc and Glc accumulation in the phloem, indicating that Suc and Glc are important carbohydrate substrates in phloem sap that are transported by VST1 to support aphid propagation and infestation. Taken together, our results demonstrated that the mutation of VST1 by genome editing can decrease aphid performance in watermelon by blocking the sugar supply obtained from phloem sap.

Ectopic Expression of a Heterologous Glutaredoxin Enhances Drought Tolerance and Grain Yield in Field Grown Maize

Drought stress is a major constraint in global maize production, causing almost 30–90% of the yield loss depending upon growth stage and the degree and duration of the stress. Here, we report that ectopic expression of Arabidopsis glutaredoxin S17 (AtGRXS17) in field grown maize conferred tolerance to drought stress during the reproductive stage, which is the most drought sensitive stage for seed set and, consequently, grain yield. AtGRXS17-expressing maize lines displayed higher seed set in the field, resulting in 2-fold and 1.5-fold increase in yield in comparison to the non-transgenic plants when challenged with drought stress at the tasseling and silking/pollination stages, respectively. AtGRXS17-expressing lines showed higher relative water content, higher chlorophyll content, and less hydrogen peroxide accumulation than wild-type (WT) control plants under drought conditions. AtGRXS17-expressing lines also exhibited at least 2-fold more pollen germination than WT plants under drought stress. Compared to the transgenic maize, WT controls accumulated higher amount of proline, indicating that WT plants were more stressed over the same period. The results present a robust and simple strategy for meeting rising yield demands in maize under water limiting conditions.

Vitis vinifera bZIP14 functions as a transcriptional activator and enhances drought stress resistance via suppression of reactive oxygen species

Background: Drought stress affects grapevine growth and development and reduces berry yield and quality. Identifying genes that are involved in the plant response to drought stress will enable the development of new grape strains that are tolerant to drought. Objective: We cloned the VvibZIP14 gene from Vitis vinifera and analyzed its role in drought resistance. Methods: Gene expression was analyzed by quantitative real-time PCR. Subcellular localization was assessed with a transient expression assay. The transactivation activity of the protein was evaluated in yeast. The physiologic role of VvibZIP14 was analyzed by overexpressing VvibZIP14 in Arabidopsis following drought stress. Hydrogen peroxide accumulation in Arabidopsis was visualized by diaminobenzidine staining. Results: Drought stress caused the accumulation of VvibZIP14, which was localized in the nucleus and had transcriptional activity. Transgenic plants showed improved resistance to drought stress and reduced electrolyte leakage compared to plants overexpressing empty vector, whereas chlorophyll content, photosystem II maximal photochemical efficiency, and net photosynthetic rate were higher. Catalase, peroxidase, and superoxide dismutase activities were also increased in VvibZIP14-overexpressing plants subjected to drought stress. Conclusions: VvibZIP14 functions as a transcription factor that confers resistance to drought stress in grape by enhancing the antioxidant response.

Microscopic, Biochemical, and Molecular Comparisons of Moderately Resistant and Susceptible Populus Genotypes Inoculated with Sphaerulina musiva

Sphaerulina musiva, the causal agent of Septoria leaf spot and stem canker, is responsible for mortality and yield loss in Populus plantations. However, little is known about the mode of infection and the mechanisms of resistance in this pathosystem. To characterize these phenomena, microscopic, biochemical, and transcriptome comparisons were performed between leaves of moderately resistant and susceptible genotypes of Populus inoculated with S. musiva conidia. Using scanning electron, cryofracture, and laser-scanning confocal microscopy, the infection and colonization of Populus leaves by S. musiva were examined across five time points (48 h, 96 h, 1 week, 2 weeks, and 3 weeks). The infection process was similar regardless of the host genotype. Differences in host colonization between susceptible and moderately resistant genotypes were apparent by 1 week postinoculation. However, the germination of conidia was greater on the susceptible than on the moderately resistant genotype (P < 0.008). Diaminobenzidine staining, a measure of hydrogen peroxide accumulation, was different (P < 0.001) between the host genotypes by 2 weeks postinoculation. Transcriptome differences between genotypes indicated that the speed and amplitude of the defense response were faster and more extensive in the moderately resistant genotype. Changes in gene expression support the microscopic and biochemical observations.

Alloxan Disintegrates the Plant Cytoskeleton and Suppresses mlo-Mediated Powdery Mildew Resistance

Recessively inherited mutant alleles of Mlo genes (mlo) confer broad-spectrum penetration resistance to powdery mildew pathogens in angiosperm plants. Although a few components are known to be required for mlo resistance, the detailed molecular mechanism underlying this type of immunity remains elusive. In this study, we identified alloxan (5,5-dihydroxyl pyrimidine-2,4,6-trione) and some of its structural analogs as chemical suppressors of mlo-mediated resistance in monocotyledonous barley (Hordeum vulgare) and dicotyledonous Arabidopsis thaliana. Apart from mlo resistance, alloxan impairs nonhost resistance in Arabidopsis. Histological analysis revealed that the chemical reduces callose deposition and hydrogen peroxide accumulation at attempted fungal penetration sites. Fluorescence microscopy revealed that alloxan interferes with the motility of cellular organelles (peroxisomes, endosomes and the endoplasmic reticulum) and the pathogen-triggered redistribution of the PEN1/SYP121 t-SNARE protein. These cellular defects are likely the consequence of disassembly of actin filaments and microtubules upon alloxan treatment. Similar to the situation in animal cells, alloxan elicited the temporary accumulation of reactive oxygen species (ROS) in cotyledons and rosette leaves of Arabidopsis plants. Our results suggest that alloxan may destabilize cytoskeletal architecture via induction of an early transient ROS burst, further leading to the failure of molecular and cellular processes that are critical for plant immunity.