Friendly Bacteria Boosts Root Growth and Phosphorus Uptake in Apple Trees

Jenn Hoskins
26th June, 2024

Friendly Bacteria Boosts Root Growth and Phosphorus Uptake in Apple Trees

This study demonstrates that inoculating the apple rootstock Malus hupehensis (pictured) with the beneficial soil bacterium Bacillus B2 significantly promotes its overall growth and enhances its ability to absorb phosphorus from the soil.

Photo adapted from: Nicolas Olejnik / CC BY (Source)

Key Findings

  • Researchers at China Agricultural University found that phosphorus-solubilizing bacteria (PSB) can help apple rootstocks absorb more phosphorus from the soil
  • Inoculating apple rootstocks with Bacillus B2 increased soluble phosphorus and flavonoid content in the soil, boosting root development and phosphorus uptake
  • The study identified a key transcription factor, MhMYB15, which is crucial for flavonoid biosynthesis and phosphorus transport, enhancing plant growth when activated by Bacillus B2
Phosphorus is a critical nutrient for plant growth and development, but its availability in soil is often limited due to its tendency to bind with other elements, making it inaccessible to plants. This challenge is particularly significant for woody plants, such as apple trees, which require ample phosphorus for optimal growth. A recent study conducted by researchers at China Agricultural University sheds light on how phosphorus-solubilizing bacteria (PSB) can enhance phosphorus availability and promote the growth of apple rootstocks[1]. The study focused on understanding the mechanisms by which PSB activate immobilized phosphorus in the soil. Researchers analyzed the microbial communities in the rhizosphere—the soil region near plant roots—of phosphate-efficient (PE) and phosphate-inefficient (PI) apple rootstocks. They discovered that PE rootstocks significantly enriched beneficial rhizobacteria. Among these, a particularly effective strain, Bacillus sp. strain 7DB1 (B2), was isolated and identified for its superior phosphorus-solubilizing capabilities. Inoculating the rhizosphere of apple rootstocks with Bacillus B2 resulted in a marked increase in soluble phosphorus and flavonoid content in the soil. This not only stimulated root development but also enhanced the plant's phosphorus uptake. Flavonoids are important plant secondary metabolites that play a role in various physiological processes, including nutrient uptake and stress responses. To delve deeper into the molecular mechanisms, the researchers conducted root transcriptome sequencing. They identified a candidate transcription factor, MhMYB15, which responded to Bacillus B2 treatment. Further experiments, including yeast one-hybrid, electrophoretic mobility shift assay, and LUC assay, confirmed that MhMYB15 could directly bind to the promoter regions of downstream genes such as chalcone synthase MhCHS2 and phosphate transporter MhPHT1;15. These genes are crucial for flavonoid biosynthesis and phosphorus transport, respectively. Transgenic experiments revealed that silencing MhMYB15 in apple rootstocks led to a failure to increase flavonoid content and phosphorus levels in the roots when treated with Bacillus B2. Consequently, plant growth was slower compared to the control group. This indicates that MhMYB15 plays a pivotal role in regulating the accumulation of flavonoids and the uptake of phosphorus, thereby influencing plant growth and development. The findings of this study align with earlier research on the role of rhizobacteria in promoting plant growth. Previous studies have highlighted the importance of the rhizomicrobiome in nutrient acquisition and plant stress responses[2]. For instance, plant-growth promoting rhizobacteria (PGPR) have been shown to enhance crop tolerance to abiotic stresses such as drought and salinity by modulating hormone levels and gene expression[3]. Additionally, the role of PSB in improving phosphorus use efficiency in crops has been well-documented, emphasizing their potential in sustainable agriculture[4]. This study extends our understanding by elucidating the specific molecular pathways through which PSB, particularly Bacillus B2, enhance phosphorus availability and promote growth in woody plants like apple rootstocks. By identifying key transcription factors and their target genes, the researchers provide valuable insights into the intricate interactions between plants and beneficial microbes. In conclusion, the study conducted by China Agricultural University demonstrates the potential of using Bacillus B2 to improve phosphorus availability and promote the growth of apple rootstocks. By activating specific molecular pathways, this PSB strain enhances flavonoid accumulation and phosphorus uptake, leading to better plant development. These findings not only contribute to our understanding of plant-microbe interactions but also offer practical solutions for improving agricultural productivity in phosphorus-limited soils.

GeneticsBiochemPlant Science

References

Main Study

1) Bacillus B2 promotes root growth and enhances phosphorus absorption in apple rootstocks by affecting MhMYB15.

Published 25th June, 2024

https://doi.org/10.1111/tpj.16893

Related Studies

2) Plant Growth-Promoting Rhizobacteria: Context, Mechanisms of Action, and Roadmap to Commercialization of Biostimulants for Sustainable Agriculture.

https://doi.org/10.3389/fpls.2018.01473

3) Plant growth-promoting rhizobacteria enhance wheat salt and drought stress tolerance by altering endogenous phytohormone levels and TaCTR1/TaDREB2 expression.

https://doi.org/10.1111/ppl.12614

4) Benefits of phosphate solubilizing bacteria on belowground crop performance for improved crop acquisition of phosphorus.

https://doi.org/10.1016/j.micres.2021.126842


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