# Wild rice-associated Vibrio promotes plant growth and exhibits genomic and phenotypic plasticity for plant adaptations

## TL;DR

A Vibrio strain helps brackish rice grow by fixing nitrogen and adapting to plant roots, revealing new insights into beneficial Vibrio-plant interactions.

## Contribution

First study to highlight Vibrio's plant growth-promoting traits and specialized genomic adaptations for plant niches.

## Key findings

- Vibrio porteresiae MSSRF30T improves Pokkali rice growth in brackish conditions through nitrogen fixation and ACC deaminase production.
- Genomic features like plant expansin and CAZymes suggest adaptation for plant-microbe interactions in Vibrio.
- MSSRF30T lacks animal-associated genome features, indicating a plant-specific lifestyle.

## Abstract

Vibrio is an important marine heterotroph, primarily studied for its pathogenesis or symbiotic relationship with marine organisms and humans. However, little is known about the association of vibrios with plants in brackish environments and their potential benefits. To address this knowledge gap, we focused on Vibrio porteresiae MSSRF30T and brackish-grown Pokkali rice as our research subjects for this study. MSSRF30T displays multifaceted plant beneficial traits, including nitrogen fixation, 1-aminocyclopropane-1-carboxylate (ACC) deaminase production, and zinc and tricalcium phosphate solubilization. Further, MSSRF30T efficiently colonizes the host roots and significantly improves the Pokkali rice growth in nitrogen-replete and nitrogen-limiting brackish conditions, highlighting its plant growth-promoting ability, a trait previously not well recognized in vibrios. Additionally, MSSRF30T can utilize various carbon-rich substrates derived from plant roots, demonstrating its metabolic adaptation to the plant rhizosphere niche. Using in planta root transcriptome analysis and whole-genome sequencing, we provide the first insights into how MSSRF30T interacts with Pokkali rice in brackish conditions. Additionally, we have identified several genome features for a plant-associated lifestyle, previously unreported in this genus. These features include plant expansin, PEP-CTERM surface anchoring with exopolysaccharides, plant-associated Hrp-type three secretion system, ACC deaminase production, PQQ-independent glucose dehydrogenase pathway for phosphate solubilization, plant-derived sugar/organic acids utilization operons, carbohydrate utilization loci, and specific plant depolymerizing CAZymes. Notably, MSSRF30T lacks key genome features critical for the animal association. Overall, this study adds new knowledge in the field of Vibrio biology, especially Vibrio-plant beneficial interactions, a relationship largely underexplored.

The genus Vibrio comprises over 150 species of marine heterotrophic bacteria, many of which are opportunistic pathogens affecting humans and marine animals. Most research has predominantly focused on pathogenic Vibrio species, often overlooking the significance of other Vibrio species inhabiting other ecological niches, such as plants, a relationship largely uncharacterized. This study focused on V. porteresiae MSSRF30T and its relationship with brackish-grown Pokkali rice. We discovered that MSSRF30T possesses multiple plant growth-promoting traits, effectively colonizes roots, and enhances plant growth in brackish conditions. Additionally, MSSRF30T possesses several genome features commonly associated with plant-microbe interactions, previously unrecognized in Vibrio species, and lacks features typically associated with animal interactions, underscoring its specialized adaptation for plant niches. For the first time, this study highlights the beneficial interactions between Vibrio and plants, emphasizing their role in promoting plant growth and health in brackish environments.