The plant beneficial rhizobacterium Achromobacter sp. 5B1 influences root development through auxin signaling and redistribution

Abstract

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.

Abscisic Acid Regulates the Root Growth Trajectory by Reducing Auxin Transporter PIN2 Protein Levels in Arabidopsis thaliana

“…as an intermediate between stressful conditions and root growth trajectory. Interestingly, previous researchers have shown that several adversities (including high salinity, hydrogen peroxide, soil hypoxia and bacteria) can lead to wavy root growth trajectory (Sun et al, 2008;Eysholdt-Derzso and Sauter, 2017;Zhou et al, 2018;Jimenez-Vazquez et al, 2020). This evidence clearly supports our assumption.…”

“…5B1 could elicit a similar phenotype as ABA does. Interestingly, the bacteria also promotes lateral root formation which may due to increased wavy frequency along growth trajectory (Jimenez-Vazquez et al, 2020). Although ABA promotes lateral roots elongation and formation as well as the wavy amplitude of growth trajectory (Figure 1).…”

“…We noticed that after transfer, the lateral roots growth was apparently promoted by ABA, since both of the lateral roots number and length were increased in the 1/2 MS medium containing ABA (Figure 1 and Supplementary Figure 10). Recently, Jimenez-Vazquez et al (2020) have reported that a beneficial rhizobacterium Achromobacter sp. 5B1 could elicit a similar phenotype as ABA does.…”

“…However, less is known about the physiological relevance and the underlying molecular mechanisms of those curved growth trajectory without typical characteristics (unlike waving or coiling). Recently, it has been reported that the root growth trajectory could be regulated by several biotic/abiotic stresses, including high salinity, hydrogen peroxide, soil hypoxia and bacteria (Sun et al, 2008;Eysholdt-Derzso and Sauter, 2017;Zhou et al, 2018;Jimenez-Vazquez et al, 2020). For example, curvature of root growth trajectory was exacerbated with increasing the NaCl medium content (Sun et al, 2008).…”

Underground allies: how bacteria stimulate plant growth by altering root development

“…They visited the site and collected soil samples from around one of the mesquite trees. In this issue of The Plant Journal, Kirán R. Jiménez‐Vázquez and colleagues present their findings on one of the bacterial strains from this soil that was of particular interest.…”