SUMMARY
Roots provide physical and nutritional support to plant organs that are above ground and play critical roles for adaptation via intricate movements and growth patterns. Through screening the effects of bacterial isolates from roots of halophyte Mesquite (Prosopis sp.) on Arabidopsis thaliana, we identified Achromobacter sp. 5B1 as a probiotic bacterium that influences plant functional traits. Detailed genetic and architectural analyses in Arabidopsis grown in vitro and in soil, cell division measurements, auxin transport and response gene expression and brefeldin A treatments demonstrated that root colonization with Achromobacter sp. 5B1 changes the growth and branching patterns of roots, which were related to auxin perception and redistribution. Expression analysis of auxin transport and signaling revealed a redistribution of auxin within the primary root tip of wild‐type seedlings by Achromobacter sp. 5B1 that is disrupted by brefeldin A and correlates with repression of auxin transporters PIN1 and PIN7 in root provasculature, and PIN2 in the epidermis and cortex of the root tip, whereas expression of PIN3 was enhanced in the columella. In seedlings harboring AUX1, EIR1, AXR1, ARF7ARF19, TIR1AFB2AFB3 single, double or triple loss‐of‐function mutations, or in a dominant (gain‐of‐function) mutant of SLR1, the bacterium caused primary roots to form supercoils that are devoid of lateral roots. The changes in growth and root architecture elicited by the bacterium helped Arabidopsis seedlings to resist salt stress better. Thus, Achromobacter sp. 5B1 fine tunes both root movements and the auxin response, which may be important for plant growth and environmental adaptation.
The rhizosphere of the great diversity of plants is a complex ecosystem that houses thousands of rhizobacteria that promote plant growth. In the current investigation, three bacteria were isolated from the root of Suaeda sp., which were evaluated to determine the ef fect of their inoculation on Arabidopsis thaliana at distances of 2 and 5 cm and in divided boxes. In the 2 cm test, we noticed that Endo10(7) and Endo10(5) stimulated the plants more than the control, while the proximity to Ecto10(6) caused them to wilt and die. However, at 5 cm, the bacterium that most promoted the development of Arabidopsis was Ecto10(6). In the divided box test, all three bacteria showed the ability to promote growth. In addition, a shade mesh assay was carried out with the inoculation of the bacteria in Solanum lycopersicum L. (Sahariana) and it was found that the promoting ef fect was also observed in the germination and growth of tomato plants. Tests were conducted to determine its ability to produce IAA, siderophores, and solubilize phosphates. Through molecular techniques it was confirmed: the identity of Ecto10(6), Endo10(7), and Endo10(5) as Aneurinibacillus migulanus, Staphylococcus sp. and Bacillus cereus, respectively. Our results provide the rationale for suggesting that these rhizobacteria may increase the growth and development of Arabidopsis thaliana and Solanum lycopersicum.
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