Nitrogen supply influences plant growth and transcriptional responses induced by Enterobacter radicincitans in Solanum lycopersicum

Abstract

The use of plant growth-promoting bacteria (PGPB) to reduce requirements for mineral nitrogen fertilization in sustainable agriculture is an important issue. We studied how reduced nitrogen fertilization affects the growth-promoting capacity of Enterobacter radicincitans, the bacteria’s root colonization behavior, and the regulation of nitrogen, phosphate and hormone marker genes in tomato (Solanum lycopersicum). Tomato seeds inoculated with 107 cfu mL−1 E. radicincitans or 0.05 M NaCl, were grown under two distinct nitrogen fertilization regimes. When treated with E. radicincitans, plant root or shoot dry weight increased by 180 %, or 150 % in high nitrogen (HN) conditions, but increased only by 120 %, or 140 % in low nitrogen (LN) conditions. HN plants were colonized by a higher number of total bacteria, including E. radicincitans, than LN plants. We found that E. radicincitans-treated plants expressed higher levels of a pathogen defense-related marker gene in LN conditions than in HN conditions. Transcription of the oxylipin biosynthesis marker genes was suppressed in E. radicincitans-treated plants under both fertilization regimes. Our findings indicate that drastic reduction in nitrogen fertilization results in modulating plant hormone signaling, thus inhibiting the optimal effect of E. radicincitans on tomato.