Rice Seeds as Sources of Endophytic Bacteria

Abstract

Endophytic bacteria are considered to originate from the external environment. To examine the hypothesis that rice (Oryza sativa, cultivar Kinuhikari) seeds are a source of endophytic bacteria, we isolated endophytic bacteria from the shoots, remains of the seeds, and roots of rice seedlings that were aseptically cultivated in vitro from surfacedisinfected seeds. Of the various bacterial strains isolated, the closest relatives, identified by 16S rRNA gene sequencing, were: Bacillus firmus, B. fusiformis, B. pumilus, Caulobacter crescentus, Kocuria palustris, Micrococcus luteus, Methylobacterium fujisawaense, Me. radiotolerans, and Pantoea ananatis. The latter three species have been detected frequently inside both rice seedlings and mature rice plants. These results indicate that rice seeds are an important source of endophytic bacteria. The bacteria that colonize the seed interior appear to infect the subsequent generation via rice seeds and become the dominant endophytic species in the mature plant.Key words: culturable endophytic bacteria, rice seed, infection from seed to shoot, 16S rRNA gene sequence Various types of microorganisms, including fungi, actinomycetes, and other bacteria, are found inside plants and designated endophytes. In general, microorganisms having visibly harmful effects on plants are not considered endophytes. Some endophytic bacteria have beneficial effects on the host, e.g., promoting plant growth, strengthening resistance to pathogens, and increasing the supply of fixed nitrogen to the plant (9). Studies are underway to exploit these beneficial features for agriculture. However, our knowledge of endophytic bacterial ecology, including the origins of these bacteria, remains incomplete.Endophytic bacteria are considered to originate from the external environment and to enter the plant through the stomata, lenticles, wounds (including broken trichomes), areas of emergence of lateral roots, and germinating radicles (12). The notion of seeds as a source of endophytic bacteria remains controversial (9). Sato (39) did not detect endophytic bacteria in rice seeds. Mundt and Hinkle (27) obtained endophytes only from the damaged seeds of 28 plant types other than rice. Endophytic bacteria were detected in cotton seeds at viable population densities that ranged from 1×10 3 to 1×105 CFU g −1 fresh weight, as well as in the seeds of sweet corn at viable population densities of <1×10 CFU g −1 fresh weight (26). Endophytic bacterial populations increased from nondetectable levels in cotton seeds to detectable levels in radicles 4 days after placing surface-disinfected cotton seeds on water agar (1).Rice (Oryza sativa) is the most important cereal crop in the world, feeding more than 50% of the global population (8). In our search for endophytic bacteria in rice plants, we detected culturable endophytic bacteria in rice seeds at viable population densities that ranged from 10 2 to 10 6 CFU g −1 fresh weight (22,31). Endophytes in seeds may be carried over to the subsequent generation. Thus, in the p...

Bacterial populations in juvenile maize rhizospheres originate from both seed and soil

“…In both plant varieties in all three substrates, a select group of seed transmitted bacteria appear to dominate the rhizosphere despite competition from soil microbes and must be well adapted to both transmission through the seed and life in the rhizosphere. These OTUs were mostly Bacteroidetes, and Proteobacteria; members of which have been previously isolated or observed as endophytes or epiphytes from a variety of plant seeds (Adams and Kloepper 2002;Ferreira et al 2008;Kaga et al 2009;Mano et al 2006;Mundt and Hinkle 1976;Truyens et al 2013), including maize (Johnston-Monje and Raizada 2011a; Liu et al 2013a). The most abundant conseq observed in maize rhizospheres belonged to OTU 212, and this was also the only OTU observed in Lenha spermospheres, suggesting a connection between seed surfaces and root surfaces.…”

Bacterial biosynthesis of 1-aminocyclopropane-1-caboxylate (ACC) deaminase, a useful trait to elongation and endophytic colonization of the roots of rice under constant flooded conditions

“…To monitor rice root and tissue colonization by this isolate and since rice seeds can be an important source of endophytic bacteria (Kaga et al 2009), we marked P. fluorescence REN 1 with gusA. Briefly for this purpose, Escherichia coli DH5α containing transposon-based b-glucuronidase (GUS) marker pNpt, which has the gusA gene under the control of a constitutive tetracycline and ampicillin resistance gene promoter (Chen et al 2010), was maintained on Luria agar plates.…”

Identification and determination of characteristics of endophytes from rice plants and their role in biocontrol of bacterial blight caused by Xanthomonas oryzae pv. oryzae

“…Evolutionary analyses were conducted in MEG 7 (Tamura et al, 2013;Kumar et al, 2016Kumar et al, ). al., 2007Mano and Morisaki, 2008;Cottyn et al, 2009;Kaga et al, 2009;Ji et al, 2014;Nhu and Diep, 2014 (Barka et al, 2002;Oliveira et al, 2003;Kang et al, 2007;Szilagyi-Zecchin et al, 2014). In addition, endophytic bacteria have been reported to be involved with other mechanisms such as competition for place and food, and antibiosis (Sturz et al, 2000;Reiter et al, 2002;Compant et al, 2005;Aravind et al, 2009;Ji et al, 2013).…”