Native bacterial endophytes promote host growth in a species-specific manner; phytohormone manipulations do not result in common growth responses.
BACKGROUND
All plants in nature harbor a diverse community of endophytic bacteria which can positively affect host plant growth. Changes in plant growth frequently reflect alterations in phytohormone homoeostasis by plant-growth-promoting (PGP) rhizobacteria which can decrease ethylene (ET) levels enzymatically by 1-aminocyclopropane-1-carboxylate (ACC) deaminase or produce indole acetic acid (IAA). Whether these common PGP mechanisms work similarly for different plant species has not been rigorously tested.


RESULTS
We isolated bacterial endophytes from field-grown Solanum nigrum; characterized PGP traits (ACC deaminase activity, IAA production, phosphate solubilization and seedling colonization); and determined their effects on their host, S. nigrum, as well as on another Solanaceous native plant, Nicotiana attenuata. In S. nigrum, a majority of isolates that promoted root growth were associated with ACC deaminase activity and IAA production. However, in N. attenuata, IAA but not ACC deaminase activity was associated with root growth. Inoculating N. attenuata and S. nigrum with known PGP bacteria from a culture collection (DSMZ) reinforced the conclusion that the PGP effects are not highly conserved.


CONCLUSIONS
We conclude that natural endophytic bacteria with PGP traits do not have general and predictable effects on the growth and fitness of all host plants, although the underlying mechanisms are conserved.
Long
Hoang Hoa
HH
Max Planck Institute for Chemical Ecology, Jena, Germany.
Schmidt
Dominik D
DD
Baldwin
Ian T
IT
D001419:Bacteria / Q000378:metabolism; D004463:Ecology; D005030:Ethylenes / Q000737:chemistry; D018506:Gene Expression Regulation, Plant; D018613:Microscopy, Confocal; D010937:Plant Growth Regulators / Q000378:metabolism*; D018521:Plant Physiological Phenomena; D018517:Plant Roots; D010957:Plasmids / Q000378:metabolism; D012336:RNA, Ribosomal, 16S / Q000737:chemistry; D032324:Solanum nigrum / Q000378:metabolism / Q000382:microbiology; D013045:Species Specificity; D013559:Symbiosis; D014026:Nicotiana / Q000382:microbiology
D005030:Ethylenes; D010937:Plant Growth Regulators; D012336:RNA, Ribosomal, 16S; C036216:ethylene