A gene expression analysis of cell wall biosynthetic genes in Malus x domestica infected by 'Candidatus Phytoplasma mali'

Abstract

Apple proliferation (AP) represents a serious threat to several fruit-growing areas and is responsible for great economic losses. Several studies have highlighted the key role played by the cell wall in response to pathogen attack. The existence of a cell wall integrity signaling pathway which senses perturbations in the cell wall architecture upon abiotic/biotic stresses and activates specific defence responses has been widely demonstrated in plants. More recently a role played by cell wall-related genes has also been reported in plants infected by phytoplasmas. With the aim of shedding light on the cell wall response to AP disease in the economically relevant fruit-tree Malus × domestica Borkh., we investigated the expression of the cellulose (CesA) and callose synthase (CalS) genes in different organs (i.e., leaves, roots and branch phloem) of healthy and infected symptomatic outdoor-grown trees, sampled over the course of two time points (i.e., spring and autumn 2011), as well as in in vitro micropropagated control and infected plantlets. A strong up-regulation in the expression of cell wall biosynthetic genes was recorded in roots from infected trees. Secondary cell wall CesAs showed up-regulation in the phloem tissue from branches of infected plants, while either a down-regulation of some genes or no major changes were observed in the leaves. Micropropagated plantlets also showed an increase in cell wall-related genes and constitute a useful system for a general assessment of gene expression analysis upon phytoplasma infection. Finally, we also report the presence of several 'knot'-like structures along the roots of infected apple trees and discuss the occurrence of this interesting phenotype in relation to the gene expression results and the modalities of phytoplasma diffusion.

Gene expression and biochemical changes of carbohydrate metabolism in in vitro micro-propagated apple plantlets infected by ‘Candidatus Phytoplasma mali’

“…Using in vitro micro-propagated apple plantlets, we have shown effects on gene expression and biochemical alterations related to phytoplasma infection. Although the in vitro system does not allow to selectively analyze different tissues or to evaluate the seasonality of gene expression and/or biochemical changes, our results and those from previous investigations show that it represents a useful system for a generalized assessment of transcriptional changes following phytoplasma infection [10].…”

“…The molecular mechanisms involved in the interaction between phytoplasmas and host plants are so far largely unknown and only recently some gene expression changes have been identified [2,6,8,10,17]. Using in vitro micro-propagated apple plantlets, we have shown effects on gene expression and biochemical alterations related to phytoplasma infection.…”

“…'Golden Delicious') was performed as reported by Guerriero et al [10]. Infection with subtype AT-2/rpX-A of the in vitro plantlets was proven by the application of the procedure described by Baric et al [15].…”

“…Considerable and tissue specific modulations were found for genes related to the cell wall metabolism, which are most likely correlated to the anatomical aberrations found on the plates of sieve tubes in infected plants [2,6,10]. Jagoueix-Eveillard et al [5] reported a down-regulation of a putative sterol-C-methyltransferase in periwinkle after infection with stolbur phytoplasma and associated this gene repression with leaf yellowing and stunting.…”

Cold-induced changes in cell wall stability determine the resistance of winter triticale to fungal pathogen Microdochium nivale

“…Therefore, abiotic and biotic stresses are often physiologically interrelated and can induce similar responses at the level of cell wall. Moreover, it was recently revealed that local and systemic acquired resistance to pathogens could be regulated by the same genetic system as the systemic acquired acclimation to abiotic stress [9,10] and that a set of genes participating in metabolism of cell wall polymers is involved in the plant defence responses [3,11,12]. A hardening of winter crops during autumn is a factor inducing the genotype-dependent resistance to infection [2,10].…”