Glucose and Stress Independently Regulate Source and Sink Metabolism and Defense Mechanisms via Signal Transduction Pathways Involving Protein Phosphorylation

Abstract

In higher plants, sugars are required not only to sustain heterotrophic growth but also to regulate the expression of a variety of genes. Environmental stresses, such as pathogen infection and wounding, activate a cascade of defense responses and may also affect carbohydrate metabolism. In this study, the relationship between sugar- and stress-activated signal transduction pathways and the underlying regulatory mechanism was analyzed. Photoautotrophically growing suspension culture cells of Chenopodium rubrum were used as a model system to study the effects of the metabolic regulator D-glucose and of different stress-related stimuli on photosynthesis, sink metabolism, and defense response by analyzing the regulation of mRNAs for representative enzymes of these pathways. Glucose as well as the fungal elicitor chitosan, the phosphatase inhibitor endothall, and benzoic acid were shown to result in a coordinated regulatory mechanism. The mRNAs for phenylalanine ammonia-lyase, a key enzyme of defense response, and for the sink-specific extracellular invertase were induced. In contrast, the mRNA for the Calvin cycle enzyme ribulose bisphosphate carboxylase was repressed. This inverse regulatory pattern was also observed in experiments with wounded leaves of C. rubrum plants. The differential effect of the protein kinase inhibitor staurosporine on mRNA regulation demonstrates that the carbohydrate signal and the stress-related stimuli independently activate different intracellular signaling pathways that ultimately are integrated to coordinately regulate source and sink metabolism and activate defense responses. The various stimuli triggered the transient and rapid activation of protein kinases that phosphorylate the myelin basic protein. The involvement of phosphorylation in signal transduction is further supported by the effect of the protein kinase inhibitor staurosporine on mRNA levels.

Strigolactones are involved in sugar signaling to modulate early seedling development in <i>Arabidopsis</i>

“…treatment, including the salicylic acid biosynthesis genes SARD1 (SAR DEFICIENT 1), DLO1 (DMR6-LIKE OXYGENASE 1), ATLTP4.4 (ARABIDOPSIS THALIANA LIPID TRANSFER PROTEIN 1), and the salicylic acid response genes encoding the WRKY family transcription factors WRKY38, WRKY44, WRKY62, and WRKY70 (Supplemental Table 5). These results are consistent with the results of other experiments, indicating that sugar induces a stress-like response and activates the expression of defense-related genes in seedlings, independently of HXK1 signaling (Ehness et al 1997;Xiao et al 2000). However, the activation of the expression of stress-related genes was completely abolished in the max2 mutant treated with glucose.…”

Alteration of plant primary metabolism in response to insect herbivory

“…Consistent with the hypothesis that import of systemic resources promotes plant defense, treatment with volatile defense signal methyl jasmonate, mechanical damage, and actual insect feeding all can increase movement of carbohydrates toward treatment sites in many plant species (Sturm and Chrispeels, 1990;Zhang et al, 1996;Ehness et al, 1997;Ohyama and Hirai, 1999;Allison and Schultz, 2005;Schultz et al, 2013). In methyl jasmonate-treated or wounded Arabidopsis, radioactively labeled carbohydrates were imported into sink leaves within hours after treatment, and were incorporated into defense-related compounds such as cinnamic acid and phenolic glycosides (Ferrieri et al, 2012).…”

Inhibition of the Plastidic ATP/ADP Transporter Protein Primes Potato Tubers for Augmented Elicitation of Defense Responses and Enhances Their Resistance against Erwinia carotovora

“…In both cases, the observed increase in soluble sugar levels was associated with constitutively increased PR gene expression (Herbers et al, 1996a(Herbers et al, , 1996b. Moreover, Glc feeding to heterotrophic cell suspensions from Chenopodium rubrum induced the immediate expression of PAL genes (Ehness et al, 1997). However, the activation mechanism of defense responses in AATP1(St) antisense tuber tissue seems to be unique and much more complex because we did not observe constitutive, preinfectional accumulation of PR gene transcripts (Fig.…”