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Ascorbate oxidation primes rice plants for enhanced defence against root-knot nematode Meloidogyne graminicola through jasmonate/ethylene-activation

ABSTRACT: Ascorbic acid (AA) is known to play a vital role in plant growth and detoxification of reactive oxygen species, however little is known about the significance of AA oxidation in plant defence against pathogens. • The role of ascorbate oxidation in rice defence against root-knot nematodes, Meloidogyne graminicola, was tested with application of AA, ascorbate oxidase (AO), dehydroascorbic acid (DHA), biosynthesis inhibitors and use of mutants. Transcriptome analysis was done on AO treated plants, and hormone measurements were executed to confirm the results. Biochemical analyses were used to study oxidative stress markers, including accumulation of H2O2, , malondialdehyde and AA/DHA.

ORGANISM(S): Oryza sativa Japonica Group

PROVIDER: GSE125427 | GEO | 2020/01/22

REPOSITORIES: GEO

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Project description:Ascorbate (vitamin C) is an important antioxidant in leaves with multiple functions in photosynthesis and its levels are tightly regulated by light quality. The majority of work to date has focussed on regulation of ascorbate levels via biosynthesis. However, the pathway of ascorbate degradation, which is localised in the apoplast may additionally play a significant role. The degradative pathway begins with ascorbate oxidation by the enzyme ascorbate oxidase (AO) and hence we have examined the impact of manipulation of ascorbate oxidase activity on the content of ascorbate and the acclimation of photosynthesis to changing light levels. Leaf ascorbate content was highly light dependent in Nicotiana tobaccum being double in high compared with low light conditions. In contrast ascorbate oxidase activity was not altered by changing light levels. Transgenic tobacco lines with reduced or enhanced AO activity exhibited no morphological phenotype and photosynthesis under high light was similarly impaired irrespective of the measured AO activity. However further investigation between AO activity and leaf acclimation to changing light intensity revealed a suite of metabolic and transcriptome changes indicating a role for the apoplastic ascorbate pool in chloroplast to nucleus communication. In all genotypes, transcripts associated with ascorbate synthesis and recycling were less abundant following transition from high to low light. However transcripts associated with glutathione recycling, light harvesting, reaction centre function and the Calvin cycle were all increased in abundance. Following the transition from high to low light increases in leaf threonate, an ascorbate degradation product, were proportional to AO activity. A number of chloroplast synthesised amino acids were significantly increased both during high light and following transfer back to LL for 12 h. Similarly, several primary carbohydrates and TCA intermediates were significantly enhanced following high light treatment. In addition to light effects, AO activity had a significant impact on ï¢-alanine, aspartate and threonine. Intriguingly, a large number of fatty acids were reduced in antisense AO and wild-type plants immediately after high light stress however the content of these compounds were significantly increased in overexpressing sense lines. We conclude that AO mediated turnover plays an important role in adjusting cellular ascorbate content to photosynthetic need in a fluctuating light environment and that light mediated signals rapidly adjust that the apoplastic ascorbate pool.

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Ascorbate oxidation primes rice plants for enhanced defence against root-knot nematode Meloidogyne graminicola through jasmonate/ethylene-activation

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