No abstract

Background: Lotus is an aquatic horticultural crop, and widely cultivated in most regions of China.Lotus is often used as a kind of an important off-season vegetable with various nutrients. Principle root of lotus is degenerated, and the role of adventitious roots (ARs) is Irreplaceable for plant growth.We found that no ARs could be formed under darkness condition, and high light significantly promote the development of root primordium. Therefore, four libraries with three light intensities were constructed to monitor metabolism changes, especially in IAA and sugar metabolism.Results: We found that ARs formation was significantly affected by light, high light intensity accelerated ARs development. The change of metabolism during ARs formation under different light intensity was evaluated according to gene expression profiling by high-throughput tag-sequencing. It was shown that more than 2.2× 10 4 genes was obtained in each library, and the expression level of most genes were distributed between 1e-01 and 1e+03 (FPKF value). Among these identified genes, 1739, 1683 and 1462 genes were up-regulated, and 1533, 995 and 834 genes were down-regulated in D/CK, E/CK and F/CK libraries respectively. In addition, we also found that 1454 and 478 genes changed expression in D/CK and F/CK libraries when compared D/CK with F/CK libraries. In F/D libraries, the transcriptional level of most differentially expressed genes was between -5~5 fold, and twenty differentially expressed genes were involved in signal transduction pathway. Twenty-eight genes related with IAA response and thirty-five genes involved in sugar metabolism were found to change expression. It was elucidated that IAA content was enhanced after seed germinated, even in darkness condition, which was responsible for ARs formation.Conclusion: The process of ARs formation was very complex, and regulated by multiple factors. The ARs formation was regulated by IAA, even in the dark, induction and developmental process could also be completed. In addition, the genes (36 genes) changed expression level in carbohydrate metabolism showed the third number, so sucrose metabolism was involved in the ARs development (expressed stage) according to genes expression and content change characteristic.

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.