It is shown that MAX3 deficiency reshapes the Arabidopsis rhizosphere by altering ABA and flavonoid accumulation, which is associated with recruitment of beneficial Pseudomonas and enhanced resistance to bacterial wilt.
Abstract
Strigolactones (SLs) are carotenoid-derived hormones that regulate plant development and abiotic stress responses, but their role in regulating plant–microbe interactions remains unclear. Here, we show that Arabidopsis thaliana loss-of-function mutants of two SL biosynthetic genes, MORE AXILLARY GROWTH 3 (MAX3) and MAX4, exhibit opposite responses to soil-borne pathogen Ralstonia solanacearum, with max3 mutants displaying enhanced resistance, whereas max4 mutants are hypersusceptible. Exogenous SL analog rac-GR24 restores resistance in max4 mutants supporting a role for canonical SL-dependent immunity, while max3 mutants mediated resistance is SL-independent. Multi-omics analyses suggest that MAX3 deficiency is associated with enhanced abscisic acid (ABA) and flavonoid pathways under natural conditions, coinciding with the enrichment of beneficial Pseudomonas in rhizosphere. Both in vitro and in planta validations suggest that the ABA-flavonoid axis cooperatively enhances Pseudomonas-mediated niche competition and antibiotic biosynthesis, thereby potentially contributing to pathogen suppression. Our findings support a model in which MAX3 is associated with the modulation of rhizosphere-mediated defense, linking hormone signaling, secondary metabolism, and microbiome assembly in the context of soil-borne disease resistance. Here the authors show that MAX3 deficiency reshapes the Arabidopsis rhizosphere by altering ABA and flavonoid accumulation, which is associated with recruitment of beneficial Pseudomonas and enhanced resistance to bacterial wilt.
Salinity is a major constraint to crop productivity. Beneficial plant–fungus interactions represent a promising strategy to enhance stress resilience. Here, we investigated fungal endophytes isolated from the roots of Oryza sativa cultivated in saline-prone marshlands of the Guadalquivir River, Spain. From a collection of 38 isolates, five salt-tolerant strains exhibiting plant growth-promoting activity were identified, including a previously uncharacterized Reticulascus sp. strain S5. Co-cultivation assays with the non-native host plant Arabidopsis thaliana demonstrated that S5 increased the root and shoot biomass under salt stress. To elucidate the underlying molecular mechanisms, a comprehensive RNA-Seq analysis of the roots and shoots under control and saline conditions was performed. Fungal colonization induced pronounced transcriptomic changes, particularly in the shoots, including rewiring of the auxin- and abscisic acid-related pathways and the induction of genes associated with cell wall remodeling. Concurrently, defense-related processes, including glucosinolate biosynthesis and ethylene signaling, were broadly repressed, suggesting attenuated stress perception in colonized plants. In the roots, S5 inoculation suppressed the expression of genes involved in root hair development and cell wall organization, indicating a fungus-driven reconfiguration of root development. Moreover, comparative analysis with Fusarium sp. K-23, a fungus that has previously been demonstrated to promote plant growth under salinity stress, revealed distinct root-associated mechanisms but convergence on a shared regulatory module in shoots involving ABA-responsive transcription factors and osmotic stress regulators. Collectively, our findings demonstrate that Reticulascus sp. S5 enhances plant salt stress tolerance through the coordinated transcriptional reprogramming of growth, hormone signaling, and stress responses, highlighting a possible potential of habitat-adapted endophytes for sustainable crop improvement.
Silvia Martínez-Fenoll, Adrián González Ortega-Villaizán, E. Rodríguez-Dobreva et al.· International Journal of Mol...· 0 citations
Plants establish intimate associations with rhizosphere microorganisms that profoundly influence their growth, development, and stress resilience. Among these, plant-growth-promoting rhizobacteria (PGPR) enhance nutrient acquisition, modulate phytohormone homeostasis and reshape root system architecture, thereby improving plant fitness. Despite extensive evidence supporting their beneficial effects, the molecular and cellular mechanisms underlying microbe-driven modulation of specific root traits remain incompletely understood. Through extensive phenotypic investigation, we established that Pseudomonas sp. M25, a previously described PGPR strain, produces a significant increase in leaf relative water content and evapotranspiration of Arabidopsis thaliana without impacting on rosette growth or photosynthetic parameters. Inoculation with M25 leads to enhanced drought tolerance, and this is associated not with changes in root architecture but with a marked increase in root hair (RH) abundance and length. The stimulation of RH development by this Pseudomonas strain is based on the genetic requirement for RH-related basic helix-loop-helix family transcription factors, including ROOT HAIR DEFECTIVE 6 (RHD6) and RHD6-LIKE 1 (RSL1), which regulate RH development via RHD6-LIKE 4 (RSL4) and RHD6-LIKE 2 (RSL2). Pseudomonas sp. M25 can partially circumvent the lack of RHD6 but requires RSL1 and the downstream transcription factors RSL2 and RSL4 to induce RH growth. These findings indicate that this bacterium can circumvent RHD6 to activate RSL4, which subsequently promotes RH growth. Our investigation identifies some essential signaling components regulated by Pseudomonas sp. M25 to optimize RH responses.
Victoria Berdion Gabarain, Ignacio Llamedo, P. D. Cáceres et al.· Plant physiology and biochem...· 0 citations
Plasmodiophora brassicae, the causal agent of clubroot disease, actively manipulates host hormone pathways to promote infection. Previous studies identified PbGH3 as a putative GH3-like effector with in vitro auxin-conjugating activity, although its biological function in planta was investigated but remained unresolved. Here, we studied the role of PbGH3 during host colonization using PbGH3 overexpressing Arabidopsis thaliana and Brassica napus lines. PbGH3 overexpression induced conserved developmental phenotypes in both species, including epinastic leaves, reduced apical dominance, enhanced lateral branching, and increased root hair formation, consistent with altered hormone balance. However, hormone profiling and exogenous auxin assays did not support a role for PbGH3 as a canonical auxin-conjugating enzyme in planta. Instead, structural analyses revealed strong similarity between PbGH3 and the Arabidopsis clade III GH3 proteins GH3.12/PBS3 and GH3.7, which are associated with salicylic acid (SA) metabolism. Consistent with this observation, loss of GH3.12/PBS3 increased susceptibility to clubroot, while expression of PbGH3 in the gh3.12 mutant background partially restored SA accumulation and reduced disease susceptibility. PbGH3 expression peaked during the early stages of infection, and overexpressing lines displayed enhanced root hair colonization by P. brassicae, suggesting a role during primary infection rather than later gall development. Together, our results support a model in which PbGH3 modulates SA-associated hormonal crosstalk and root morphology that could be harnessed by the clubroot pathogen to ensure host colonization. These findings provide new insight into how P. brassicae manipulate host hormone homeostasis during infection.
This review critically examines the current knowledge on the functional roles of arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria in pistachio production and identified the key knowledge gaps and research priorities required to improve the consistency, scalability, and field validation of microbiome-based approaches for sustainable pistachio production under increasingly challenging environmental conditions.
L. Vera, J. Retamal-Salgado, G. Tortella et al.· Plants· 0 citations
It was demonstrated that cucumber roots absorbed IAA production by Bacillus subtilis B21, thereby activating the expression of IAA signalling and ROS detoxification that had been inhibited by salt stress, providing new mechanistic insights into PGPR-mediated plant salt tolerance.
Jia-Wei Song, Yi-Jing Tian, Yu Song et al.· Plant, Cell and Environment· 0 citations
Apple rust, caused by the fungal pathogen Gymnosporangium yamadae, leads to substantial yield losses and significant economic damage. In the rust-resistant cultivar Malus ‘Profusion’, rust infection triggers anthocyanin synthesis at infection sites as a defense mechanism to restrict fungal proliferation. Although small noncoding RNAs (miRNAs) play important roles in regulating anthocyanin biosynthesis, their specific functions under rust stress remain poorly characterized. In this study, small RNA sequencing revealed that miR166a is a key rust-responsive regulator. Its direct targeting and negative regulation of MpATHB8 were confirmed through luciferase assays, GUS staining, and gene expression analyses. Functional validation via transient and stable transformation in Malus demonstrated that suppressing miR166a expression using short tandem target mimics or overexpressing MpATHB8 promoted anthocyanin accumulation and enhanced resistance to rust. In contrast, overexpressing miR166a or silencing MpATHB8 suppressed anthocyanin synthesis and increased susceptibility to the pathogen. Further evidence indicates that the MpATHB8 protein activates anthocyanin biosynthesis by binding to and inducing the promoter of MpMYB10b. These findings reveal a miR166a-MpATHB8-MpMYB10b regulatory module that enhances rust resistance through anthocyanin metabolism in M. ‘Profusion’. Our findings provide novel insights into the miRNA-mediated regulation of anthocyanin metabolism and facilitate the breeding of rust-resistant and anthocyanin-enriched Malus cultivars.
