The mutulisc aoatin of tall fescue (Festuca arundinacca) with seed-borne Hnal symbionts (endophytes)

A highly conserved sequence was found in rRNA gene internal transcribed spacer 1 (ITS1) among flowering plant species. The sequence, GGCRY-(4 to 7 n)-GYGYCAAGGAA (where Y = C or T; R = G or A) is located in the central region of ITS1, and is present in published sequences from a wide range of flowering plants. The rest of ITS1 is highly variable in sequence. Therefore, the conserved motif within ITS1 may have a key function in the processing of rRNA gene transcripts. Furthermore, identification of such a conserved motif will help facilitate alignment of sequences for phylogenetic analysis.

Bamboo mosaic potexvirus (BaMV) supports the replication and encapsidation of a single-stranded satellite RNA (satBaMV). Full-length infectious cDNA clones of sat-BaMV variants with a 0.7 to 7.5% difference in nucleotide sequence were constructed, and in vitro transcripts were co-inoculated with BaMV RNA to barley protoplasts. Co-inoculation with BSL6 satBaMV transcripts resulted in a greatly reduced accumulation of genomic and subgenomic RNAs whereas co-inoculation with the prototype BSF4 or other variants did not. satBaMV variant BSL6-mediated interference occurred at the genomic RNA, subgenomic RNA, and capsid protein levels whereas the synthesis of minus strand was not significantly affected. Attenuation of the BaMV symptoms also was observed in Chenopodium quinoa and Nicotiana benthamiana plants co-inoculated with BSL6 satBaMV. In protoplasts of barley and N. benthamiana, BSF4 and BSL6 variants replicated at a similar level whereas in the inoculated leaves of C. quinoa and N. benthamiana BSL6 accumulated to a much lower level than BSF4, and was encapsidated. BSL6 satBaMV was rarely detected in the systemic leaves of N. benthami-ana co-inoculated with BaMV RNA, indicating that BSL6 satBaMV may be a movement-inefficient variant. It is suggested that this variant may provide a potential source for both resistance against BaMV and insights into the interactions of satellite RNA, helper virus, and symptom expression.

Satellite RNA of bamboo mosaic potexvirus (satBaMV) is a linear RNA molecule which encodes a 20-kDa nonstructural protein. Sequences of seven different satBaMV isolates from bamboo hosts in three genera showed 0.7% to 7.5% base variation which spanned the whole RNA molecule. However, the putative 20-kDa open reading frame was all preserved in these isolates. The phylogenetic relationship based on the nucleotide sequence did not show particular grouping of satBaMV from the host in one genus; neither was the grouping of satBaMV evident by location of sampling. Putative secondary structures of the 3' untranslated regions showed a basic pattern with conserved hexanucleotides (ACCUAA) and polyadenylation signal (AAUAAA) located in the loop regions. Although the satBaMV-encoded 20-kDa protein is a nonstructural protein, its predicted secondary structure contains eight-stranded beta-sheets which may form "jelly-roll" structure similar to that found in capsid protein encoded by satellite virus of panicum mosaic virus.

No abstract