Elevating Ascorbate in Arabidopsis Stimulates the Production of Abscisic Acid, Phaseic Acid, and to a Lesser Extent Auxin (IAA) and Jasmonates, Resulting in Increased Expression of DHAR1 and Multiple Transcription Factors Associated with Abiotic Stress Tolerance.

Sean M Bulley,William Laing,Janine M Cooney

doi:10.3390/ijms22136743

Sean M Bulley, William Laing + Show 1 more

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https://doi.org/10.3390/ijms22136743

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Abstract

Gene expression and phytohormone contents were measured in response to elevating ascorbate in the absence of other confounding stimuli such as high light and abiotic stresses. Young Arabidopsis plants were treated with 25 mM solutions of l-galactose pathway intermediates l-galactose (l-gal) or l-galactono-1,4-lactone (l-galL), as well as L-ascorbic acid (AsA), with 25 mM glucose used as control. Feeding increased rosette AsA 2- to 4-fold but there was little change in AsA biosynthetic gene transcripts. Of the ascorbate recycling genes, only Dehydroascorbate reductase 1 expression was increased. Some known regulatory genes displayed increased expression and included ANAC019, ANAC072, ATHB12, ZAT10 and ZAT12. Investigation of the ANAC019/ANAC072/ATHB12 gene regulatory network revealed a high proportion of ABA regulated genes. Measurement of a subset of jasmonate, ABA, auxin (IAA) and salicylic acid compounds revealed consistent increases in ABA (up to 4.2-fold) and phaseic acid (PA; up to 5-fold), and less consistently certain jasmonates, IAA, but no change in salicylic acid levels. Increased ABA is likely due to increased transcripts for the ABA biosynthetic gene NCED3. There were also smaller increases in transcripts for transcription factors ATHB7, ERD1, and ABF3. These results provide insights into how increasing AsA content can mediate increased abiotic stress tolerance.

Highlights

L-ascorbic acid (AsA) is an essential dietary nutrient which humans cannot synthesize due to mutations within the L-gulono-g-lactone oxidase (GLO) gene [1] (GLO catalyzes the last step in vitamin C biosynthesis), elevating AsA in plant foods for human nutrition is of interest to plant breeding [2]
Network analysis and gene ontologies suggested links with phytohormones such as abscisic acid and jasmonates so we measured a subset of phytohormones as well. From this we present evidence of how gene transcripts of known and deduced AsA related genes change in response to an increase in AsA concentration in the absence of external abiotic stimuli to obtain greater insights into the regulation of AsA metabolism and how it is involved in abiotic stress tolerance
Arabidopsis plants were sprayed with a perfume sprayer to wetness four times over a h period with mM solutions of L-galactose pathway intermediates L-gal (21 days post sowing plants; experiment 1) or L-galL (38 days post sowing plants; experiment 2 and 3), as well as 25 mM AsA (27 days post sowing plants experiment 3)

Summary

Introduction

L-ascorbic acid (AsA) is an essential dietary nutrient (vitamin C) which humans cannot synthesize due to mutations within the L-gulono-g-lactone oxidase (GLO) gene [1] (GLO catalyzes the last step in vitamin C biosynthesis), elevating AsA in plant foods for human nutrition is of interest to plant breeding [2]. A major group of AsA requiring enzymes are the diverse 2-oxoglutarate-dependent dioxygenase class of enzymes which number in the thousands, and which ACC oxidase belongs to [12,13,14]. This means that changes in AsA can have pleiotropic effects by altering the activities of multiple enzymes. In animals AsA is involved in epigenetic regulation, via demethylation of nucleotides and histones [15] This has been established in mammals through the identification of Ten-Eleven-Translocation (TET) enzymes [16,17,18], which are 2-oxoglutarate- and AsA-dependent dioxygenases. It is unknown if there are functioning enzymes in plants

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