NnLAC17, a Gene Related to Lignin Synthesis, is Involved in Adventitious Root Formation in the Seedlings of Lotus (Nelumbo Nucifera Gaertn)

Abstract BarkgroundAdventitious roots (ARs), which are considered as an important member of root system, have an unmatched status in plant growth and metabolism due to the degeneration of primary roots in lotus. The regulation of AR formation was previously revealed and multiple factors were recognized to be involved in this biological process. ResultsIn the present study, we sought to assess the effect of sucrose on AR formation. Based on our results, lignin metabolism, which is regulated by the sucrose signal transduction pathway, is involved in AR development. The lignification degree of the AR primordium was weaker in plants treated with 20 g/L sucrose than in control plants. However, based on the microstructural observation of the AR developmental process, 50 g/L sucrose promoted the lignification process. Lignin content, including monomer and polymer lignin, was determined in the present study. Compared with control plants, the monomer (containing 30%–45% S type and 55%–70% G type) and polymer lignin contents were lower in plants treated with 20 g/L sucrose and higher in plants treated with 50 g/L sucrose. The precursors of monomer lignin were identified in four libraries of differential developmental stages in seedlings using LC-MS/MS technique. The contents of four metabolites, including p-coumaric acid, caffeate, sinapinal aldehyde and ferulic acid for monomer lignin synthsis were lower in the GL50 library than in the GL20 library. Further analysis revealed that the gene expression of these four metabolites had no novel difference in the GL50/GL20 libraries. However, NnLAC17, a gene involved in polymer lignin synthesis, had a higher expression in the GL50 library than in the GL20 library. ConclusionsTherefore, NnLAC17 was cloned, and the overexpression of NnLAC17 was found to directly result in a decrease in AR number in transgenic Arabidopsis plants. These findings suggest that NnLAC17, which is relevant to lignin synthesis, is involved in AR formation in lotus seedlings.