Plant Tissue Localization and Morphological Conversion of upon Initial Interaction with L.

The genus is recognized as plant growth-promoting bacteria that exert beneficial effects on the host plant and is morphologically converted into cyst-like cells (i.e., c-form) in association with poly-β-hydroxybutyrate (PHB) accumulation in the cells under stress conditions. We constructed , labeled with reporter genes (, ) and examined the plant tissue localization along with a morphological conversion into the c-form upon its initial interaction with onion seedlings ( L.). The PHB granules in the cells were easily detected under fluorescence as "black holes", rendering it possible to monitor the morphological conversion from vegetative to the c-form cells. The results showed that the cells on the surface of the roots and bulbs (underground stem) began converting at three days following inoculation and that the cell conversion was significantly advanced with time along with the cell population increase. The endophytic infection of into the bulb tissues was also confirmed, although these likely constituted vegetative cells. Moreover, the morphological conversion into the c-form was induced under nitrogen-restricted conditions. Analysis of the biochemical properties of the cells during cell conversion revealed that the acetylene reduction activity correlated positively with the PHB accumulation in the cells converting into the c-form under nitrogen-restricted conditions.