Balance of callose metabolism in phytoplasma/plant interaction

Callose deposition is a calcium-mediated process occurring in the sieve elements in response to both abiotic and biotic stresses, such as wounding or pathogens infection. On the other hand, callose synthesis normally occurs during growing conditions in plant tissues, having an important role in the process of phloem cell maturation. Even if callose accumulation at the sieve plates has been widely reported in plant affected by phytoplasmas, fine distribution of callose barriers in the phloem as well as callose quantification have been not investigated in detail. In this work, an integrated approach, based on the combined use of microscopic, biochemical and immunological analyses, has been adopted to investigate callose presence and distribution in leaf midribs of Solanum lycopersicum (‘cv Micro-Tom’) infected by ‘Candidatus Phytoplasma solani’ (group 16 SrXII, subgroup A) and Arabidopsis thaliana (ecotype Col-0) infected by ‘Candidatus Phytoplasma asteris’ (group 16SrI, subgroup B). Obtained results demonstrated site-specific changes in callose distribution and metabolism in the infected tissues, and they express a balancement between plant-defence strategies and plant growth and survival under a biotrophic interaction.