Phytochrome Mediated Responses in Agrobacterium fabrum: Growth, Motility and Plant Infection

Peng Xue,Tilman Lamparter,Elizaveta Averbukh,Thomas Roeder,Yingnan Bai,Gregor Rottwinkel,Patrick Scheerer,Yuanyuan Ma,Norbert Krauß

doi:10.1007/s00284-021-02526-5

Abstract

The soil bacterium and plant pathogen Agrobacterium fabrum C58 has two phytochrome photoreceptors, Agp1 and Agp2. We found that plant infection and tumor induction by A. fabrum is down-regulated by light and that phytochrome knockout mutants of A. fabrum have diminished infection rates. The regulation pattern of infection matches with that of bacterial conjugation reported earlier, suggesting similar regulatory mechanisms. In the regulation of conjugation and plant infection, phytochromes are active in darkness. This is a major difference to plant phytochromes, which are typically active after irradiation. We also found that propagation and motility were affected in agp1− and agp2− knockout mutants, although propagation was not always affected by light. The regulatory patterns can partially but not completely be explained by modulated histidine kinase activities of Agp1 and Agp2. In a mass spectrometry-based proteomic study, 24 proteins were different between light and dark grown A. fabrum, whereas 382 proteins differed between wild type and phytochrome knockout mutants, pointing again to light independent roles of Agp1 and Agp2.

Highlights

Soil bacteria of the genus Agrobacterium can transfer genes into plants and thereby induce the formation of plant tumors
In earlier studies we found no effect of phytochromes on A. fabrum growth in liquid culture, but in these studies growth was followed for 6 h only [14]
We provide evidence for the involvement of bacterial phytochromes in the regulation of plant infection, in motility and growth in liquid culture

Summary

Introduction

Soil bacteria of the genus Agrobacterium can transfer genes into plants and thereby induce the formation of plant tumors. A first clear Agrobacterium phytochrome response was found by a computer based co-distribution study [15, 16]. In this investigation, we searched for Agp and Agp BLAST homologs in 43 related species that belong to the Rhizobiales. When strains with Ti plasmid were used, conjugation was drastically reduced by red or far-red light and in agp1− or agp2− knockout mutants. Studies with complementation strains were more complex than expected but showed that the observed mutant effects were clearly the result of the loss of phytochrome

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Conclusion