Leaf Vitamin C Contents Modulate Plant Defense Transcripts and Regulate Genes That Control Development through Hormone Signaling[W]

Abstract

Vitamin C deficiency in the Arabidopsis mutant vtc1 causes slow growth and late flowering. This is not attributable to changes in photosynthesis or increased oxidative stress. We have used the vtc1 mutant to provide a molecular signature for vitamin C deficiency in plants. Using statistical analysis, we show that 171 genes are expressed differentially in vtc1 compared with the wild type. Many defense genes are activated, particularly those that encode pathogenesis-related proteins. Furthermore, transcript changes indicate that growth and development are constrained in vtc1 by the modulation of abscisic acid signaling. Abscisic acid contents are significantly higher in vtc1 than in the wild type. Key features of the molecular signature of ascorbate deficiency can be reversed by incubating vtc1 leaf discs in ascorbate. This finding provides evidence that many of the observed effects on transcript abundance in vtc1 result from ascorbate deficiency. Hence, through modifying gene expression, vitamin C contents not only act to regulate defense and survival but also act via phytohormones to modulate plant growth under optimal conditions.

The multifaceted role of ABA in disease resistance

“…Based on the finding that application of the antioxidant ascorbate can restore susceptibility to B. cinerea [20], it is tempting to speculate that sitiens-induced resistance is caused by an interaction between the xanthophyll cycle and the ROS-buffering ascorbate-gluthatione cycle (Figure 3). In support of this, a mechanistic link between ABA biosynthesis and ascorbate has been demonstrated [21], which showed that low ascorbate in the Arabidopsis vtc1 (vitamin C1) mutant stimulates ABA production. The sitiens mutation in tomato blocks the last step in ABA biosynthesis.…”

“…The conversion of violaxanthin into zeaxanthin is catalyzed by violaxanthin de-epoxidase (VDE) and requires oxidation of ascorbate into de-hydro ascorbate. As a result, reduced levels of ascorbate in the vtc1 (vitamin C1) mutant stimulate ABA biosynthesis [21]. By contrast, enhanced VDE activity antagonizes ABA production, reduces ascorbate levels and promotes conversion of reduced glutathione (GSH) into oxydized glutathione (GSSG).…”

“…This leads to a reduction of the redox-buffering capacity in the cell and enables augmented ROS accumulation. Violaxanthin is converted into xanthoxin through a series of isomerization reactions and a dioxygenation step by 9-cisepoxycarotenoid di-oxygenase (NCED) [21], which cleaves xanthoxin from the C 40 carotenoid. The final steps in ABA biosynthesis, the conversion of xanthoxin into ABA, occur in the cytoplasm and involve a dehydrogenase (xanthoxin:NAD + oxidoreductase) (mutated in aba2) and the ABA aldehyde oxidase (affected in the Arabidopsis mutants aba3, aao3 [Arabidopsis aldehyde oxidase 3] and the sitiens mutant of tomato [52][53][54]).…”

Examination of Correlations Between Several Biochemical Components and Powdery Mildew Resistance of Flax Cultivars

“…It also inhibited the oxidation of coniferyl alcohol by peroxidase leads to synthesis of lignin, another important defense-related compound (Ye et al, 1990). Pastori et al (2003) showed that many defense genes, particularly those that encode pathogenesis related-proteins were activated in Arabidopsis mutant deficient in biosynthesis of ascorbic acid. In the present study, a negative correlation was observed between ascorbic acid content and PM severity (Table 4).…”

The Timing of Senescence and Response to Pathogens Is Altered in the Ascorbate-Deficient Arabidopsis Mutant vitamin c-1

“…The vtc1 mutant, isolated by its sensitivity to ozone, has lower activity of the AsA biosynthetic enzyme GDPMan pyrophosphorylase, resulting in a 70% lower AsA content compared to the wild type (Conklin et al, 1999). Two recent studies on this mutant have demonstrated that both leaf photosynthesis and the capacity of the antioxidant system are largely un-changed (Veljovic-Jovanovic et al, 2001), while some plant defense-related transcripts are up-regulated (Pastori et al, 2003). The effect of low AsA on xanthophyll cycle activity was studied recently in the AsAdeficient mutant vitamin c-2 (vtc2; Mü ller-Moulé et al, 2002).…”