Publikationen - Molekulare Signalverarbeitung

Chrysanthemum chlorotic mottle viroid (CChMVd) RNA (398–401 nucleotides) can form hammerhead ribozymes that play a functional role in its replication through a rolling-circle mechanism. In contrast to most other viroids, which adopt rod-like or quasi-rod-like secondary structures of minimal free energy, the computer-predicted conformations of CChMVd and Peach latent mosaic viroid (PLMVd) RNAs are branched. Moreover, the covariations found in a number of natural CChMVd variants support that the same or a closely related conformation exists in vivo. Here we report that the CChMVd natural variability also supports that the branched conformation is additionally stabilized by a kissing-loop interaction resembling another one proposed in PLMVd from in vitro assays. Moreover, site-directed mutagenesis combined with bioassays and progeny analysis showed that: (1) single CChMVd mutants affecting the kissing loops had low or no infectivity at all, whereas infectivity was recovered in double mutants restoring the interaction; (2) mutations affecting the structure of the regions adjacent to the kissing loops reverted to wild type or led to rearranged stems, also supporting their interaction; and (3) the interchange between 4 nucleotides of each of the two kissing loops generated a viable CChMVd variant with eight mutations. PAGE analysis under denaturing and nondenaturing conditions revealed that the kissing-loop interaction determines proper in vitro folding of CChMVd RNA. Preservation of a similar kissing-loop interaction in two hammerhead viroids with an overall low sequence similarity suggests that it facilitates in vivo the adoption and stabilization of a compact folding critical for viroid viability.

Various octadecanoids and derived compounds have been identified in potato leaves. However, information regarding jasmonate hydroxylated forms in stolons or tubers is scarce. We investigated endogenous jasmonates in stolon material ofSolarium tuberosum cv. Spunta. Stolons and incipient tubers were collected from 8 weeks old plants. The material was cut into apical regions and stolons. We identified jasmonic acid (JA), methyl jasmonate, 11-OH-JA, 12-OH-JA, 12-oxo-phytodienoic acid (OPDA) and a conjugate. The content of JA and 12OH-JA decreased in the apical region but remained high in stolons during tuberization. Thus the apical region might be a site of JAs-utilization or metabolization and stolons might supply JAs to that region. The content of 12-OH-JA was higher than that of 11-OH-JA in all stages analyzed, both in apical regions and stolons. However, these compounds showed a different time-course in the apical region: while 11-OH-JA increased, 12-OH-JA decreased. Thus, JA from leaves or roots could be transported as 12-OH-JA to the apical region, stimulating tuber formation.