Herbaspirillum rubrisubalbicans, a mild pathogen impairs growth of rice by augmenting ethylene levels

Abstract

Herbaspirillum rubrisubalbicans decreases growth of rice. Inoculation of rice with H. rubrisubalbicans increased the ACCO mRNA levels and ethylene production. The H. rubrisubalbicans rice interactions were further characterized by proteomic approach. Herbaspirillum rubrisubalbicans is a well-known growth-promoting rhizobacteria that can also act as a mild phyto-pathogen. During colonisation of rice, RT-qPCR analyses showed that H. rubrisubalbicans up-regulates the methionine recycling pathway as well as phyto-siderophore synthesis genes. mRNA levels of ACC oxidase and ethylene levels also increased in rice roots but inoculation with H. rubrisubalbicans impaired growth of the rice plant. A proteomic approach was used to identify proteins specifically modulated by H. rubrisubalbicans in rice and amongst the differentially expressed proteins a V-ATPase and a 14-3-3 protein were down-regulated. Several proteins of H. rubrisubalbicans were identified, including the type VI secretion system effector Hcp1, suggesting that protein secretion play a role colonisation in rice. Finally, the alkyl hydroperoxide reductase, a primary scavenger of endogenous hydrogen peroxide was also identified. Monitoring the levels of reactive oxygen species in the epiphytic bacteria by flow cytometry revealed that H. rubrisubalbicans is subjected to oxidative stress, suggesting that the alkyl hydroperoxide reductase is an important regulator of redox homeostasis in plant-bacteria interactions.

Modulation of defence and iron homeostasis genes in rice roots by the diazotrophic endophyte Herbaspirillum seropedicae

“…seropedicae showed induction of ascorbate peroxidases 35 , though the genes encoding these enzymes were not affected in our RNA-seq analyses. Moreover, seven days after inoculation, ROS levels in Herbaspirillum rubrisubalbicans attached to rice roots had increased suggesting that the bacteria were subject to oxidative stresses 36 . In this work, two peroxidase genes were induced by H .…”

“…Furthermore, Valdameri et al . 36 detected induction of ACC oxidase in rice plants inoculated with the pathogen H . rubrisubalbicans .…”

Systems Biology of Plant-Microbiome Interactions

“…Among the Streptomyces(Viaene et al, 2016), S. lividans can protect plants against fungal pathogens(Meschke and Schrempf, 2010), while S. scabiei causes rot on roots and tubers of potatoes, beets, and carrots(Hiltunen et al, 2009). Members of the Herbasprillum rubrisubalbicans species are usually mild pathogens in sugarcane, sorghum, and rice(Valdameri et al, 2017), while H. seropedicae and some strains of…”

What Did We Learn From Plant Growth-Promoting Rhizobacteria (PGPR)-Grass Associations Studies Through Proteomic and Metabolomic Approaches?

“…However, few proteomics studies have identified bacterial proteins related to nitrogen fixation or nitrogen metabolism during grass colonization. Only two proteomics studies have identified proteins involved in nitrogen fixation and ammonium assimilation, NifH and glutamine synthetase (GS), respectively, which are up-regulated in rice roots colonized by the H. seropedicae SmR1 (Alberton et al, 2013) or the H. rubrisubalbicans M1Sm300 (Valdameri et al, 2017). These findings suggest that the cells are under nitrogen-fixing conditions after 7 days of inoculation.…”