Gluconacetobacter diazotrophicus Elicits a Sugarcane Defense Response Against a Pathogenic Bacteria Xanthomonas albilineans

Abstract

A new role for the plant growth-promoting nitrogen-fixing endophytic bacteria Gluconacetobacter diazotrophicus has been identified and characterized while it is involved in the sugarcane-Xanthomonas albilineans pathogenic interactions. Living G.diazotrophicus possess and/or produce elicitor molecules which activate the sugarcane defense response resulting in the plant resistance to X. albilineans, in this particular case controlling the pathogen transmission to emerging agamic shoots. A total of 47 differentially expressed transcript derived fragments (TDFs) were identified by cDNA-AFLP. Transcripts showed significant homologies to genes of the ethylene signaling pathway (26%), proteins regulates by auxins (9%), beta-1,3 Glucanase proteins (6%) and ubiquitin genes (4%), all major signaling mechanisms. Results point toward a form of induction of systemic resistance in sugarcane-G. diazotrophicus interactions which protect the plant against X. albilineans attack.

Keywords: Gluconacetobacter diazotrophicus; Xanthomonas albilineans; elicitors; sugarcane.

Figure 1

Amplification of the alb gene of X.albilineans (A and B) and the 23S ribosomal RNA gene from G. diazotrophicus (C and D) during the interactions sugarcane-X. albilineans- G. diazotrophicus. 1–8: Treatments (see Materials and Methods and Table 2). C⁺:PCR of X.a or G.d colonies growing in their respective solid medium. C^-:PCR of sterile culture media for X.a or G.d without bacterial inoculation.

Figure 2

Section of AFLP-cDNA gels (9% polyacrilamide) showing differentially expressed TDFs (transcript derived fragments) in the Saccharum spp- Xanthomonas albilineans-Gluconacetobacter diazotrophicus interaction. Bands were evidenced by AgNO₃ staining (Promega, USA), and the size of differential TDF was determined by direct sequencing. Copy primers A: AseI-1/TaqI-1; B: AseI-1/TaqI-2; C: AseI-1/TaqI-3; D: AseI-2/TaqI-1 I.- Plants inoculated firstly with G.d and after 7 days with the pathogenic bacterium X.a. II.- Plants infected with the pathogen X.a and after 7 days inoculated with G.d. T0.- Control treatments, just after cross inoculation: T1 - one day; T2- three days; T3- seven days.

Figure 3

RNA blot analysis for differentially amplified TDFs identified during the Saccharum spp.- G. diazotrophicus - X. albilineans interactions. RNA blots were performed with 10 µg of total RNA per lane. T0 (immediately after cross infection), T1, T2 and T3 time (one, three and seven days after cross infection), respectively. For codices description see Table 3.