Medicago truncatula root developmental changes by growth-promoting microbes isolated from Fabaceae, growing on organic farms, involve cell cycle changes and WOX5 gene expression
Both root nodules and the rhizosphere of Fabaceae plants grown on organic farms are a rich source of bacteria, mainly from the families Enterobacteriaceae and Pseudomonadaceae. The enhanced root system growth in M. truncatula after inoculation with selected bacteria includes an increase of nuclei in the cell cycle S phase and a reduction in phase G2 as well as an enhanced expression of the WOX5 gene.
Synthetic fertilizers and pesticides are commonly used to improve plant quality and health. However, it is necessary to look for other efficient and also environmentally safe methods. One such method involves the use of bacteria known as plant growth-promoting bacteria (PGPB). Seventy-two bacterial isolates from the rhizospheric soil and root nodule samples of legumes, including bean, alfalfa, lupine and barrel medic, grown on an organic farm in Western Pomerania (Poland) were screened for their growth-promoting capacities and 38 selected isolates were identified based on 16S rRNA gene sequencing. The analysis showed the isolates to represent 17 strains assigned to 6 families: Enterobacteriaceae, Pseudomonadaceae, Xanthomonadaceae, Rhizobiaceae, Bacillaceae and Alcaligenaceae. Pot experiments showed that 13 strains, capable of producing indole compounds from tryptophan in vitro, could significantly enhance the root and shoot weight of 10-week-old Medicago truncatula seedlings. Compared to non-inoculated seedlings, the root system of inoculated ones was more branched; in addition, the root length, surface area and, especially, the root volume were higher. The 24-h root inoculation with the three selected strains increased the nuclei population in the G1 and S phases, decreased it in the G2 phase and enhanced the WUSCHEL-related Homeobox5 (WOX5) gene expression in root tips and lateral zones. The “arrest” of nuclei in the S phase and the enhancement of the WOX5 gene expression were observed to gradually disappear once the bacterial suspension was rinsed off the seedling roots and the roots were transferred to water for further growth. This study shows that the nodules and rhizosphere of legumes grown on organic farms are a rich source of different PGPB species and provides new data on the ability of these bacteria to interfere with cell cycle and gene expression during the root development.
Keywords16S rRNA identification DNA replication Nodules PGPB traits Plant growth promotion Rhizosphere WOX5 expression
Plant growth-promoting bacteria
This work was partially supported by the National Scientific Centre (NCN) Grant no. NN310784140. We would like to express our gratitude to Professor Jan Kępczyński for making the flow cytometer of the Department Plant Physiology and Genetic Engineering available and for reading and commenting on the manuscript draft. We thank Anna Orłowska for her help in WOX gene expression experiment, and Katarzyna Łagowska and Paulina Król for technical assistance in flow cytometry experiment. We are indebted to Teresa Radziejewska for linguistic assistance.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
- Abberton M (2010) Enhancing the role of legumes: potential and obstacles. In: Abberton M, Conant R, Batello C (eds) Integrated crop management, vol. 11: Grassland, carbon sequestration: management, policy and economics. Proceedings of the workshop on the role of grassland carbon sequestration in the mitigation of climate change, Rome, pp 177–187Google Scholar
- Avinash TS, Rai RV (2014) Antifungal activity of plant growth promoting rhizobacteria against Fusarium oxysporum and Phoma sp. of cucurbitaceae. In: Kharwar RN, Upadhyway R, Dubey NK, Radhuwanshi R (eds) Microbial diversity and biotechnology in food security. Springer, New Delhi, pp 257–264Google Scholar
- Barea JM (2015) Future challenges and perspectives for applying microbial biotechnology in sustainable agriculture based on a better understanding of plant–microbiome interactions. J Soil Sci Plant Nutr 15(2):261–282Google Scholar
- Couillerot O, Combes-Meynet E, Pothier JF, Bellvert F, Challita E, Poirier MA, Rohr R, Comte G, Moënne-Loccoz Y, Prigent-Combaret C (2011) The role of the antimicrobial compound 2,4-diacetylphloroglucinol in the impact of biocontrol Pseudomonas fluorescens F113 on Azospirillum brasilense phytostimulators. Microbiology 157:1694–1705PubMedCrossRefPubMedCentralGoogle Scholar
- Dwivedi D, Johri BN (2003) Antifungals from fluorescent pseudomonads: biosynthesis and regulation. Curr Sci 85(12):1693–1703Google Scholar
- FAOSTAT (2016). http://faostat3.fao.org/browse/Q/QC/S. Accessed 01 Oct 2016
- Holt JG, Kreig NR, Sneath PHA, Staley JT, Wiliams ST (1994) Bergey’s manual of determinative bacteriology. Williams and Wilkins, MarylandGoogle Scholar
- Kumar A, Bahadur I, Maurya BR, Raghuwanshi R, Meena VS, Singh DK, Dixit J (2015) Does a plant growth promoting rhizobacteria enhance agricultural sustainability. J Pure Appl Microbiol (JPAM) 9(1):715–724Google Scholar
- Le Mire G, Nguyen ML, Fassotte B, du Jardin P, Verheggen F, Delaplace P, Jijakli MH (2016) Implementing plant biostimulants and biocontrol strategies in the agroecological management of cultivated ecosystems: a review. Biotechnol Agron Soc Environ 20(S1):299–313Google Scholar
- Orłowska A, Kępczyńska E (2018) Identification of Polycomb Repressive Complex1, Trithorax group genes and their simultaneous expression with WUSCHEL, WUSCHEL-related Homeobox5 and SHOOT MERISTEMLESS during the induction phase of somatic embryogenesis in Medicago truncatula Gaertn. Plant Cell Tissue Org Cult 134:345–356CrossRefGoogle Scholar
- Pikovskaya RI (1948) Mobilization of phosphorus in soil in connection with the vital activity of some microbial species. Mikrobiologiya 17:362–370Google Scholar
- Sultan NS, Raipat BS, Sinha MP (2013) Survival of plant growth promoting rhizobacteria (PGPR) in soil under pesticide stress. ISESCO J Sci Technol 9(16):82–88Google Scholar
- Van Loon LC, Bakker PAHM (2006) Induced systemic resistance as a mechanism of disease suppression by rhizobacteria. In: Siddiqui ZA (ed) PGPR: biocontrol and biofertilization. Springer, Dordrecht, pp 39–66Google Scholar
- Wahyudi AT, Astuti RP, Widyawati A, Meryandini A, Nawangsih AA (2011) Characterization of Bacillus sp. strains isolated from rhizosphere of soybean plants for their use as potential plant growth for promoting rhizobacteria. J Microbiol Antimicrob (JMA) 3(2):34–40Google Scholar
- Willer H, Lernoud J (2017) Organic Agriculture Worldwide 2017: current statistic. BIOFACH, February 15Google Scholar