Phloem Cytochemical Modification and Gene Expression Following the Recovery of Apple Plants from Apple Proliferation Disease

Abstract

Recovery of apple trees from apple proliferation was studied by combining ultrastructural, cytochemical, and gene expression analyses to possibly reveal changes linked to recovery-associated resistance. When compared with either healthy or visibly diseased plants, recovered apple trees showed abnormal callose and phloem-protein accumulation in their leaf phloem. Although cytochemical localization detected Ca(2+) ions in the phloem of all the three plant groups, Ca(2+) concentration was remarkably higher in the phloem cytosol of recovered trees. The expression patterns of five genes encoding callose synthase and of four genes encoding phloem proteins were analyzed by quantitative real-time reverse transcription-polymerase chain reaction. In comparison to both healthy and diseased plants, four of the above nine genes were remarkably up-regulated in recovered trees. As in infected apple trees, phytoplasma disappear from the crown during winter, but persist in the roots, and it is suggested that callose synthesis/deposition and phloem-protein plugging of the sieve tubes would form physical barriers preventing the recolonization of the crown during the following spring. Since callose deposition and phloem-protein aggregation are both Ca(2+)-dependent processes, the present results suggest that an inward flux of Ca(2+) across the phloem plasma membrane could act as a signal for activating defense reactions leading to recovery in phytoplasma-infected apple trees.

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

“…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.…”

“…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.…”

“…Most typical symptoms of phytoplasmainduced disease are small and/or bronze reddish leaves, enlarged stipules, leaf-rosette formations, virescent flowers with abnormal number of petals, and decreased fruit quality [1]. At the tissue level, host plants show anatomical aberrations such as callose accumulation on the plates of sieve tubes and in some cases phloem tissue proliferation and necrosis [2]. Reduced stomatal conductance has also been reported together with the inhibition of photosystem II (PS II) activity [3,4].…”

HflB Gene-Based Phytopathogenic Classification of ‘Candidatus Phytoplasma mali’ Strains and Evidence that Strain Composition Determines Virulence in Multiply Infected Apple Trees

“…Ultrastructural, cytochemical, and gene expression analyses of phloem of healthy, visibly diseased, and recovered apple trees revealed various differences. Recovered trees are characterized by the presence of hydrogen peroxide (H 2 O 2 ), callose and phloem protein accumulation, and the upregulation of genes involved in synthesis of callose and phloem protein (Musetti et al 2004(Musetti et al , 2010). …”

Acquired Tolerance in Apricot Plants that Stably Recovered from European Stone Fruit Yellows

“…Abiotic and biotic agents already known to induce systemic acquired resistance have been also hypothesized to be involved in recovery (1,13,44). Recent results obtained by investigating the physiological and genetic bases of recovery (37)(38)(39)(40) supported a strict correlation between recovery and a type of acquired or induced resistance in the host plant. Very recently, it has been shown that AP induced an increase in salicylate in apple plants, followed by a decline accompanied by a subsequent increase of jasmonic acid (JA) during recovery (42).…”