Publikationen - Molekulare Signalverarbeitung

The shape of tomato fruits is closely correlated to microtubule organization and the activity of microtubule associated proteins (MAP), but insights into the mechanism from a cell biology perspective are still largely elusive. Analysis of tissue expression profiles of different microtubule regulators revealed that functionally distinct classes of MAPs are highly expressed during fruit development. Among these, several members of the plant-specific MAP70 family are preferably expressed at the initiation stage of fruit development. Transgenic tomato lines overexpressing SlMAP70 produced elongated fruits that show reduced cell circularity and microtubule anisotropy, while SlMAP70 loss-of-function mutant showed an opposite effect with flatter fruits. Microtubule anisotropy of fruit endodermis cells exhibited dramatic rearrangement during tomato fruit development, and SlMAP70-1 is likely implicated in cortical microtubule organization and fruit elongation throughout this stage by interacting with SUN10/SlIQD21a. The expression of SlMAP70 (or co-expression of SlMAP70 and SUN10/SlIQD21a) induces microtubule stabilization and prevents its dynamic rearrangement, both activities are essential for fruit shape establishment after anthesis. Together, our results identify SlMAP70 as a novel regulator of fruit elongation, and demonstrate that manipulating microtubule stability and organization at the early fruit developmental stage has a strong impact on fruit shape.

Chrysanthemum chlorotic mottle viroid (CChMVd) (398–401 nt) belongs to genus Pelamoviroid, family Avsunviroidae and, like other members of this family, replicates in plastids through a rolling-circle mechanism involving hammerhead ribozymes. CChMVd RNA adopts a branched conformation stabilized by a kissing-loop interaction, resembling peach latent mosaic viroid in this respect. Chrysanthemum is the only natural and experimental host for CChMVd, which in the most sensitive varieties induces leaf mottling and chlorosis, delay in flowering, and dwarfing. The viroid has been found in major chrysanthemum growing areas including Europe and Asia. There are natural variants in which the change (UUUC→GAAA) mapping at a tetraloop in the CChMVd branched conformation is sufficient to change the symptomatic phenotype into a nonsymptomatic one without altering the viroid titer. Preinfection with nonsymptomatic variants prevents challenge inoculation with symptomatic ones. Moreover, experimental coinoculation with symptomatic and nonsymptomatic CChMVd variants results in symptomless phenotypes only when the latter is in vast excess, thus indicating its lower fitness.

This chapter focuses on Ophioviridae family whose sole member genus is Ophiovirus. The member species of the genus include Citrus psorosis virus (CPsV), Freesia sneak virus(FreSV), Lettuce ring necrosis virus (LRNV), and Mirafiori lettuce big-vein virus (MiLBVV).The single stranded negative/possibly ambisense RNA genome is divided into 3–4 segments, each of which is encapsidated in a single coat protein (43–50 kDa) forming filamentous virions of about 3 nm in diameter, in shape of kinked or probably internally coiled circles of at least two different contour lengths. Ophioviruses can be mechanically transmitted to a limited range of test plants, inducing local lesions and systemic mottle. The natural hosts of CPsV, ranunculus white mottle virus (RWMV), MiLBVV, and LRNV are dicotyledonous plants of widely differing taxonomy. CPsV has a wide geographical distribution in citrus in the Americas, in the Mediterranean and in New Zealand. FreSV has been reported in two species of the family Ranunculacae from Northern Italy, and in lettuce in France and Germany. Tulip mild mottle mosaic virus (TMMMV) has been reported in tulips in Japan. LRNV is closely associated with lettuce ring necrosis disease in The Netherlands, Belgium, and France, and FreSV has been reported in Europe, Africa, North America and New Zealand.

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