Expression of the nifH Gene of a Herbaspirillum Endophyte in Wild Rice Species: Daily Rhythm during the Light-Dark Cycle

Abstract

The expression of nitrogenase genes of Herbaspirillum sp. B501 associated in shoot (leaf and stem) of wild rice, Oryza officinalis, was studied by means of reverse transcription-PCR (RT-PCR) targeted at the nifH gene. RT-PCR analyses indicate that nifH transcript was detected exclusively from nitrogen-fixing cells of gfp-tagged strain B501gfp1 in both free-living and endophytic states by using a constitutive gfp gene transcript as a positive control. Transcription of nifH and nitrogen fixation in free-living cells were induced maximally at a 2% O 2 concentration and repressed in free air (21% O 2 ). nifH transcription was monitored in the endophytic cells by using total RNA extracted from B501gfp1-inoculated wild rice plants during daily light-dark cycles. The level of nifH transcription in planta varied dramatically, with a maximum during the light period. Moreover, the light radiation enhanced nifH expression even in free-living cells grown in culture. These results suggest that in planta nitrogen fixation by the endophyte shows a daily rhythm determined by the plant's light environment.

Oryza sativa rice plants contain molecules that activate different quorum-sensing N-acyl homoserine lactone biosensors and are sensitive to the specific AiiA lactonase

“…A few years ago, it has been reported that root exudates from several plant secrete compounds that mimic AHLs (Teplitski et al, 2000;Gao et al, 2003;Mathesius et al, 2003) as these can activate bacterial AHL biosensors; however, their chemical structure and precise biological source are currently unknown. It appears that densities of endophytic bacteria, if rice colonization-infection experiments are performed, are usually low, lower than 10 7 cells g À1 (James et al, 2002;You et al, 2005). In addition through the use of the specific AHL AiiA-lactonase, it was observed that these compounds are very sensitive to the enzyme and therefore are most likely AHLs or have a very related lactone structure.…”

Expressed nifH Genes of Endophytic Bacteria Detected in Field-Grown Sweet Potatoes (Ipomoea batatas L.)

“…In experiments similar to the present ones, only one alternative nitrogenase gene was found to be preferentially expressed in spite of the existence of remarkably diverse nifH sequences in the termite gut microbial community 23) . Many environmental factors such as the O2 concentration and nitrogen sources 12,42) might limit or regulate nifH gene expression in plants.…”

Symbiotic Bradyrhizobium japonicum Reduces N 2 O Surrounding the Soybean Root System via Nitrous Oxide Reductase

“…Beacon Designer software (Premier Biosoft International, Palo Alto, CA) was used to design the nosZ primer set (nosZ2F, 5Ј-GTCGTC ATCTTCAACCTCAAG; nosZ2R, 5Ј-TATTCATGCCATGCGGATTG). Total RNA was prepared as described previously (53). Quantitative reverse transcription-PCR analysis was carried out by the i-Cycler optical system (Bio-Rad Laboratories, Inc., Tokyo, Japan) as described previously (53).…”

“…Total RNA was prepared as described previously (53). Quantitative reverse transcription-PCR analysis was carried out by the i-Cycler optical system (Bio-Rad Laboratories, Inc., Tokyo, Japan) as described previously (53).…”