This paper confirms our findings of late expression of T3SS genes at late stages of disease development in planta, reported previously in Microbiology http://mic.sgmjournals.org/content/early/2012/05/15/mic.0.058610-0.abstract
As a friend said before: "It feels so good to have your results confirmed by an independent group, using a different approach".
This publication also explores the metabolic adaptations of R. solanacearum during colonization and multiplication in planta, focusing on the particular case of sucrose uptake and catabolism.
Although much is known about the signals that trigger transcription of virulence genes in plant pathogens, their prevalence and timing during infection are still unknown. In this work, we address these questions by analysing expression of the main pathogenicity determinants in the bacterial pathogen R. solanacearum. We set up a quantitative, non-invasive luminescent reporter to monitor in planta transcription from single promoters in the bacterial chromosome. We show that the new reporter provides a real-time measure of promoter output in vivo -either after re-isolation of pathogens from infected plants or directly in situ- and confirm that the promoter controlling exopolysaccharide synthesis is active in bacteria growing in the xylem. We also provide evidence that hrpB -the master regulator of type III secretion system genes- is transcribed in symptomatic plants. Quantitative RT-PCR assays demonstrate that hrpB and type III effector transcripts are abundant at late stages of plant infection suggesting that their function is required throughout disease. Our results challenge the widespread view in R. solanacearum pathogenicity that the type III secretion system - and thus injection of effector proteins- is only active to manipulate plant defences at the first stages of infection, and that their expression is turned down when bacteria reach high cell densities and exopolysaccharide synthesis starts.
Via Freddy Monteiro