engleski

Auxin-induced recovery of phytoplasma-infected periwinkle

Phytoplasmas (genus ‘Candidatus Phytoplasma’) are endocellular plant pathogenic bacteria that cause numerous economically important diseases, and in many cases cause death of their plant hosts. Many research attempts were made in order to find a suitable method to fight against phytoplasma diseases. Infections caused by phytoplasmas lead to developmental disorders in infected hosts via deregulation of developmentally important genes while the presence of these pathogens disturbs the normal transport through the phloem causing numerous physiological and biochemical changes in infected hosts including the changes in plant growth regulators balance. This fact was the basis for the idea to try to eliminate phytoplasmas by treating infected plants with auxins. In vitro grown Catharanthus roseus shoots infected with 3 different ‘Candidatus Phytoplasma’species were treated with two auxins. Tested plant growth regulators, indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA), induced remission of symptoms (recovery) in all phytoplasma-infected plants. The time period and concentration of the auxin needed to induce recovery was dependent on the ‘Candidatus Phytoplasma’species and the type of auxin. IBA-treatment eliminated ‘Ca. P. asteris’ (strain HYDB) from the host while ‘Ca. P. solani’ (strain SA-I) and ‘Ca. P. ulmi’ (strain EY-C) persisted in the host tissue despite the obvious recovery of infected plant. To elucidate the possible mechanism of host recovery and ‘Ca. P. asteris’ elimination from C. roseus shoots caused by indole-3-butyric acid (IBA)-treatment, H2O2 and related enzymes, stem anatomy and callose deposition in phloem tissue, endogenous auxin levels and general methylation levels were measured and compared for non-infected periwinkles, periwinkles infected with different ‘Candidatus Phytoplasma’ species and phytoplasma-recovered periwinkles. Differences in methylation of the host plant genome after the treatment with auxin revealed that epigenetic changes induced in periwinkle by IBA treatment might be responsible for the elimination of ‘Ca. P. asteris’ from the infected plant. In nature, rare cases of spontaneously recovered plant species are known. However, the molecular mechanism of phytoplasma recovered periwinkles upon the treatment with IBA is different than the proposed recovery mechanism in spontaneously recovered plants where peroxide and related enzymes are the proposed cause of the recovery. Our results show that in the case of some ‘Candidatus Phytoplasma’ species, auxin-treatment could be used to eliminate phytoplasmas from plants.

bacteria; elimination

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