Health & Environmental Research Online (HERO)


Print Feedback Export to File
1761998 
Journal Article 
Microbe-Associated Molecular Patterns-Triggered Root Responses Mediate Beneficial Rhizobacterial Recruitment in Arabidopsis 
Lakshmanan, V; Kitto, SL; Caplan, JL; Hsueh, YiH; Kearns, DB; Wu, YuS; Bais, HP 
2012 
1 
Plant Physiology
ISSN: 0032-0889
EISSN: 1532-2548 
160 
3 
1642-1661 
22972705 
WOS:000310584200037 
This study demonstrated that foliar infection by Pseudomonas
syringae pv tomato DC3000 induced malic acid (MA) transporter (ALUMINUM-ACTIVATED MALATE
TRANSPORTER1 [ALMT1]) expression leading to increased MA titers in the rhizosphere of Arabidopsis
(Arabidopsis thaliana). MA secretion in the rhizosphere increased beneficial rhizobacteria
Bacillus subtilis FB17 (hereafter FB17) titers causing an induced systemic resistance response in
plants against P. syringae pv tomato DC3000. Having shown that a live pathogen could induce an
intraplant signal from shoot-to-root to recruit FB17 belowground, we hypothesized that pathogen-
derived microbe-associated molecular patterns (MAMPs) may relay a similar response specific to
FB17 recruitment. The involvement of MAMPs in triggering plant innate immune response is well
studied in the plant's response against foliar pathogens. In contrast, MAMPs-elicited plant
responses on the roots and the belowground microbial community are not well understood. It is
known that pathogen-derived MAMPs suppress the root immune responses, which may facilitate
pathogenicity. Plants subjected to known MAMPs such as a flagellar peptide, flagellin22 (flg22),
and a pathogen-derived phytotoxin, coronatine (COR), induced a shoot-to-root signal regulating
ALMT1 for recruitment of FB17. Micrografts using either a COR-insensitive mutant (coi1) or a
flagellin-insensitive mutant (fls2) as the scion and ALMT1(pro):beta-glucuronidase as the
rootstock revealed that both COR and flg22 are required for a graft transmissible signal to
recruit FB17 belowground. The data suggest that MAMPs-induced signaling to regulate ALMT1 is
salicylic acid and JASMONIC ACID RESISTANT1 (JAR1)/JASMONATE INSENSITIVE1 (JIN1)/MYC2
independent. Interestingly, a cell culture filtrate of FB17 suppressed flg22-induced MAMPs-
activated root defense responses, which are similar to suppression of COR-mediated MAMPs-
activated root defense, revealing a diffusible bacterial component that may regulate plant immune
responses. Further analysis showed that the biofilm formation in B. subtilis negates suppression
of MAMPs-activated defense responses in roots. Moreover, B. subtilis suppression of MAMPs-
activated root defense does require JAR1/JIN1/MYC2. The ability of FB17 to block the MAMP-
selicited signaling pathways related to antibiosis reflects a strategy adapted by FB17 for
efficient root colonization. These experiments demonstrate a remarkable strategy adapted by
beneficial rhizobacteria to suppress a host defense response, which may facilitate rhizobacterial
colonization and host-mutualistic association.