Gene expression analysis of maize seedlings (DKB240 variety) inoculated with plant growth promoting bacterium Herbaspirillum seropedicae

Herbaspirillum seropedicae is an endophytic diazotrophic bacterium. We investigated the gene expression of Zea mays roots inoculated with the plant growth-promoting bacterium H. seropedicae. Maize seedlings (cv. DKB240) were inoculated with H. seropedicae strain SmR1, grown in sterilized sand and collected 1, 4, 7 and 10 days after inoculation (DAI). The study was repeated three times and it was found that the number of lateral roots was significantly higher in inoculated seedlings than in controls at 7 and 10 DAI. The transcript levels of 10 maize genes (actin1, chalcone synthase, ent-copalyl diphosphate synthase, ent-kaurene oxidase, gibberellin 20 oxidase 4, auxin transporter-like protein 1, mitogen-activated protein kinase 5, respiratory burst oxidase proteins A, B and C) were quantified by qRT-PCR. A significant increase of transcript levels was observed for ent-kaurene oxidase and for respiratory burst oxidase protein C in inoculated seedlings compared to controls at 4 DAI. It was concluded that at the beginning of the interaction, the presence of Herbaspirillum seropedicae SmR1 in maize roots modulates transiently the expression of one gene involved in gibberellin biosynthesis pathway and another gene of NADPH oxidase.