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Front. Microbiol. | doi: 10.3389/fmicb.2019.02422

Overexpression of Chromosome Partitioning Gene parA in Azorhizobium caulinodans ORS571 Alters Bacteroid Morphotype in Sesbania rostrata Stem Nodules

Hsiao-Lin Chien1,  Chi-Te Liu1, 2*, Wan-Zhen Huang1, Ming-Yen Tsai1 and Chiung-Hsiang Cheng3
  • 1Institute of Biotechnology, College of Bioresources and Agriculture, National Taiwan University, Taiwan
  • 2Agricultural Biotechnology Research Center, Academia Sinica, Taiwan
  • 3School of Veterinary Medicine, National Taiwan University, China

Azorhizobium caulinodans ORS571 is a diazotroph that forms N2-fixing nodules on the roots and stems of the tropical legume Sesbania rostrata. Deletion of the parA gene of this bacterium results in cell cycle defects, pleiomorphic cell shape, and formation of immature stem nodules on its host plant. In this study, we constructed a parA overexpression mutant (PnptII-parA) to complement a previous study and provide new insights into bacteroid formation. We found that overproduction of ParA did not affect growth, cell morphology, chromosome partitioning, or vegetative nitrogen fixation in the free-living state. Under symbiosis, however, distinctive features, such as a single swollen bacteroid in one symbiosome, relatively narrow symbiosome space, and polyploid cells were observed. The morphotype of the PnptII-parA bacteroid is reminiscent of terminal differentiation in some IRLC indeterminate nodules, but S. rostrata is not thought to produce the NCR peptides that induce terminal differentiation in rhizobia. In addition, the transcript patterns of many symbiosis-related genes elicited by PnptII-parA were different from those elicited by the wild type. Accordingly, we propose that the particular symbiosome formation in PnptII-parA stem-nodules is due to cell cycle disruption caused by excess ParA protein in the symbiotic cells during nodulation.

Keywords: chromosome partitioning, Nitrogen Fixation, bacteroid formation, nodule development, Cell Cycle, plant defense

Received: 08 May 2019; Accepted: 07 Oct 2019.

Copyright: © 2019 Chien, Liu, Huang, Tsai and Cheng. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Chi-Te Liu, Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan, chiteliu@ntu.edu.tw