The Type III Secretion System (T3SS) is a Determinant for Rice-Endophyte Colonization by Non-Photosynthetic <i>Bradyrhizobium</i>

Abstract

Plant associations by bradyrhizobia have been detected not only in leguminous plants, but also in non-leguminous species including rice. Bradyrhizobium sp. SUTN9-2 was isolated from Aeschynomene americana L., which is a leguminous weed found in the rice fields of Thailand. This strain promoted the highest total rice (Oryza sativa L. cultivar Pathum Thani 1) dry weight among the endophytic bradyrhizobial strains tested, and was, thus, employed for the further characterization of rice-Bradyrhizobium interactions. Some known bacterial genes involved in bacteria-plant interactions were selected. The expression of the type III secretion component (rhcJ), type IV secretion component (virD4), and pectinesterase (peces) genes of the bacterium were up-regulated when the rice root exudate was added to the culture. When SUTN9-2 was inoculated into rice seedlings, the peces, rhcJ, virD4, and exopolysaccharide production (fliP) genes were strongly expressed in the bacterium 6–24 h after the inoculation. The gene for glutathione-S-transferase (gst) was slightly expressed 12 h after the inoculation. In order to determine whether type III secretion system (T3SS) is involved in bradyrhizobial infections in rice plants, wild-type SUTN9-2 and T3SS mutant strains were inoculated into the original host plant (A. americana) and a rice plant (cultivar Pathum Thani 1). The ability of T3SS mutants to invade rice tissues was weaker than that of the wild-type strain; however, their phenotypes in A. americana were not changed by T3SS mutations. These results suggest that T3SS is one of the important determinants modulating rice infection; however, type IV secretion system and peces may also be responsible for the early steps of rice infection.

Mutualistic co‐evolution of T3SSs during the establishment of symbiotic relationships between Vigna radiata and Bradyrhizobia

“…T3SSs deliver T3Es directly into the extracellular environment or into the cytosol of eukaryotic host cells (Cornelis & Van Gijsegem, 2000;He, Nomura, & Whittam, 2004;Pallen, Chaudhuri, & Henderson, 2003). Previous reports showed that T3SSs may have either positive or negative effects on leguminous plant-rhizobia symbiosis (Freiberg et al, 1997;Hueck, 1998;Okazaki et al, 2010;Piromyou et al, 2015;Skorpil et al, 2005). Moreover, the T3SS of Sinorhizobium fredii NGR234 is functional and is involved in the determination of the host range of nodulation (Viprey, Greco, Golinowski, Broughton, & Perret, 1998).…”

Effects of strategic tillage and plant hormone treatments on wheat-associated microbial communities

“…Motility, chemotaxis, production of cell-wall degrading products and lipopolysaccharide formation are among the observed traits for bacteria to infect and adapt to inside plants (Piromyou et al, 2015). Comparative genomic or metagenomic analyses together with mutational studies have confirmed the importance of these traits.…”

“…SUTN9-2, which originally formed symbiotic relationships with the leguminous weed Aeschynomene americana (Piromyou et al, 2015). Pectinesterase expression in this bacterium was up-regulated after being inoculated on rice seedlings (Piromyou et al, 2015). In addition to the abovementioned traits, Kost et al (2014) found that oxalotrophy, the capacity of utilizing oxalate as a carbon source, is required for the successful colonization of B. phytofirmans PsJN on lupin and maize plants.…”

“…For example, pectinase is an important determinant modulating rice early infection by the plant growth promoting bacteria Bradyrhizobium sp. SUTN9-2, which originally formed symbiotic relationships with the leguminous weed Aeschynomene americana (Piromyou et al, 2015). Pectinesterase expression in this bacterium was up-regulated after being inoculated on rice seedlings (Piromyou et al, 2015).…”

“…However, T3SS and T4SS are crucial for Bradyrhizobium sp. SUTN9-2 (isolated from the leguminous grass Aeschynomene americana L.) to colonize the roots of rice seedlings (Piromyou et al, 2015). The function of T6SS is largely unknown but they may also be important for plantendophytic interactions (Mitter et al, 2013;Sessitsch et al, 2012).…”