title: Phytoplasma-triggered Ca(2+) influx is involved in sieve-tube blockage.
abstract: Phytoplasmas are obligate, phloem-restricted phytopathogens that are disseminated by phloem-sap-sucking insects. Phytoplasma infection severely impairs assimilate translocation in host plants and might be responsible for massive changes in phloem physiology. Methods to study phytoplasma- induced changes thus far provoked massive, native occlusion artifacts in sieve tubes. Hence, phytoplasma-phloem relationships were investigated here in intact Vicia faba host plants using a set of vital fluorescent probes and confocal laser-scanning microscopy. We focused on the effects of phytoplasma infection on phloem mass-flow performance and evaluated whether phytoplasmas induce sieve-plate occlusion. Apparently, phytoplasma infection brings about Ca(2+) influx into sieve tubes, leading to sieve-plate occlusion by callose deposition or protein plugging. In addition, Ca(2+) influx may confer cell wall thickening of conducting elements. In conclusion, phytoplasma effectors may cause gating of sieve-element Ca(2+) channels leading to sieve-tube occlusion with presumptive dramatic effects on phytoplasma spread and photoassimilate distribution.
authors.affiliation: Department of Agriculture and Environmental Sciences, University of Udine, Udine, Italy. Rita.Musetti@uniud.it
authors.forename: Rita
authors.initials: R
authors.lastname: Musetti
authors.forename: Stefanie V
authors.initials: SV
authors.lastname: Buxa
authors.forename: Federica
authors.initials: F
authors.lastname: De Marco
authors.forename: Alberto
authors.initials: A
authors.lastname: Loschi
authors.forename: Rachele
authors.initials: R
authors.lastname: Polizzotto
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Kogel
authors.forename: Aart J E
authors.initials: AJ
authors.lastname: van Bel
mesh_terms: D002118:Calcium / Q000378:metabolism*; D018613:Microscopy, Confocal; D052585:Phloem / Q000378:metabolism* / Q000382:microbiology*; D045582:Phytoplasma / Q000472:pathogenicity*; D031307:Vicia faba / Q000378:metabolism* / Q000382:microbiology*
chemical_list: D002118:Calcium