Abstract
Viroids are small, non-coding, pathogenic RNAs with a significant ability of adaptation to several basic cellular processes in plants. TFIIIA-7ZF, a splicing variant of transcription factor IIIA, is involved in replication of nuclear-replicating viroids by DNA-dependent polymerase II. We overexpressed NbTFIIIA-7ZF from Nicotiana benthamiana in tobacco (Nicotiana tabacum) where it caused morphological and physiological deviations like plant stunting, splitting of leaf petioles, pistils or apexes, irregular branching of shoots, formation of double-blade leaves, deformation of main stems, and modification of glandular trichomes. Plant aging and senescence was dramatically delayed in transgenic lines. Factors potentially involved in viroid degradation and elimination in pollen were transiently depressed in transgenic leaves. This depressed “degradome” in young plants involved NtTudor S-like nuclease, dicers, argonoute 5, and pollen extracellular nuclease I showing expression in tobacco anthers and leaves. Analysis of the “degradome” in tobacco leaves transformed with either of two hop viroids confirmed modifications of the “degradome” and TFIIIA expression. Thus, the regulatory network connected to TFIIIA-7ZF could be involved in plant pathogenesis as well as in viroid adaptation to avoid its degradation. These results support the hypothesis on a significant impact of limited TFIIIA-7ZF on viroid elimination in pollen.
Highlights
Published: 23 February 2022Transcription factor IIIA (TFIIIA) is a special member of the zinc finger family of nucleic acid-binding proteins with multiple functions
A statistically significant increase of TFIIIA levels in 7ZF tobacco leaves was measured in comparison to control untransformed tobacco (Figure S3a)
Plants transformed with NbTFIIIA-7ZF surprisingly showed numerous morphological deviations and abnormalities (Figure 1), which were not observed in control tobaccos
Summary
Transcription factor IIIA (TFIIIA) is a special member of the zinc finger family of nucleic acid-binding proteins with multiple functions. TFIIIA is essential for the DNAdependent RNA polymerase III-based transcription of 5S rRNA. It binds both 5S rDNA and 5S rRNA [2,3]. The TFIIIA gene contains a 5S rRNA-derived exon in all representative land plant species [4,5]. Skipping of this exon leads to the full TFIIIA protein with nine zinc fingers (TFIIIA-9ZF). TFIIIA and its shorter variant are modulated upon viroid infection and are obviously potent interactive members of the zinc finger family
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