Small Noncoding RNAs in Agrobacterium tumefaciens
During the last decade, small noncoding RNAs (ncRNAs) have emerged as essential post-transcriptional regulators in bacteria. Nearly all important physiological and stress responses are modulated by ncRNA regulators, such as riboswitches, trans-acting small RNAs (sRNAs), and cis-antisense RNAs. Recently, three RNA-seq studies identified a total of 1534 candidate ncRNAs from Agrobacterium tumefaciens, a pathogen and biotechnology tool for plants. Only a few ncRNAs have been functionally characterized in A. tumefaciens, and some of them appear to be involved in virulence. AbcR1 regulates multiple ABC transporters and modulates uptake of a quorum-sensing inhibitor produced by plants. RNA1111, a Ti plasmid-encoded sRNA, might regulate the dispersal of the Ti plasmid and virulence. In addition, a chromosomally encoded sRNA Atr35C is induced by the vir gene regulator VirG and its expression is affected by iron, manganese, and hydrogen peroxide, suggesting a possible role in oxidative stress responses and Agrobacterium–plant interactions. Progress in ncRNA functional analysis is slow, likely resulting from innate challenges, such as poor sequence conservation and imperfect base-pairing between sRNAs and mRNAs, which make computational target predictions inefficient. Advances in single-cell-based RNA-seq and proteomics approaches would provide valuable tools to reveal regulatory networks involving ncRNA regulators.
The authors thank Abbagail Johnson, Juan Carlos Martinez-Nicolas, Alan Eggenberger, and Jonah Miller for their assistances. This work was partially supported by the USDA National Institute of Food and Agriculture, Hatch project number #IOW05162, by State of Iowa funds, and by Charoen Pokphand Indonesia.
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