Effects of Exogenous Auxins on Tomato Tissue Infected With the Citrus Exocortis Viroid

Leaf disks, stem segments, and callus cultures from healthy and CEVinfected plants of a hybrid of Lycopersicon esculentum and Lycopersicon peruvianum were cultured in vitro under different hormone regimes. The differences in response observed when the medium was supplemented with auxins, alone or in combination with cytokinins, suggest that the inability of CEV-infected cells to respond to auxins might be involved in the development of the pathogenic syndrome caused by CEV

Evolutionary Constraints to Viroid Evolution

We suggest that viroids are trapped into adaptive peaks as the result of adaptive constraints. The first one is imposed by the necessity to fold into packed structures to escape from RNA silencing. This creates antagonistic epistases, which make future adaptive trajectories contingent upon the first mutation and slow down the rate of adaptation. This second constraint can only be surpassed by increasing genetic redundancy or by recombination. Eigen’s paradox imposes a limit to the increase in genome complexity in the absence of mechanisms reducing mutation rate. Therefore, recombination appears as the only possible route to evolutionary innovation in viroids

Influencia de virus y similares en el desarrollo de yemas de cítricos cultivadas “in vitro”

Se estudio el efecto de seis agentes patógenos en el desarrollo de yemas de citricos cultivadas in vitro y la obtención de plantas a partir de las mismas. Las enfermedades estudiadas fueron la tristeza causada por un closterovirus (CTV), el infectious variegation causado por un virus ilar (CIVV), el vein enation y la psoriasis que son enfermedades de etiologia desconocida transmisibles por injerto, y la exocortis y la cachexia producidos por un complejo de viroides

Changes in the Pathway of Ethylene Production Following Citrus Exocortis Viroid Infection in Tomato Plants

Ethylene production was stimulated during the systemic reaction of Rutgers tomato to citrus exocortis viroid (CEV) infection. The increase in ethylene production of CEV-infected leaf discs was parallel to the increase in 1-aminocyclopropane-1-carboxylic acid (ACC) production, and content. Moreover, the capacity to convert ACC into ethylene (ethylene forming enzyme activity) in CEV-infected leaves also increased. The blockage of ACC synthase with aminooxyacetic acid (AOA) completely prevented the viroid-induced production of ethylene, thus indicating that this enzyme is the primary controlling step of ethylene biosynthesis acted upon in viroid infection. The increased ethylene-forming enzyme (EFE) activity acts as a secondary contributor to the enhanced production of ethylene

Identification and Characterization of a Variant of Citrus viroid V (CVd-V) in Seminole Tangelo

Previous studies on Atalantia citroides, a citrus relative that appeared to be immune to viroid infection, revealed the existence of a new viroid, which was designated tentatively as Citrus viroid-V (CVd-V) and has been proposed as a new member of the genus Apscaviroid within the family Pospiviroidae. Biological indexing of a Seminole tangelo tree on the Etrog citron indicator followed by sPAGE analysis revealed the presence of a viroid that has been characterized as a new variant of CVd-V. The variant has 97.6% sequence identity with the reference sequence of CVd-V and shows three characteristics: (I) two compensatory changes that modify an A-U base pair between the upper and lower “strands” into a G-C base pair, (II) a U→A change located in a loop that does not seem to disturb the viroid secondary structure, and (III) two sets of changes located in the upper and lower strands that result in a rearrangement of the base pairing between the upper and lower strands. Infectivity studies performed with an artificial mutant revealed the existence of structural constraints in the region in which major differences between CVd-V and the Seminole tangelo variant were identified