NnWOX1-1, NnWOX4-3, and NnWOX5-1 of lotus (Nelumbo nucifera Gaertn)promote root formation and enhance stress tolerance in transgenic Arabidopsis thaliana.

Background: Adventitious roots (ARs) represent an important organ system for water and nutrient uptake in lotus plants because of degeneration of the principal root. The WUSCHEL-related homeobox (WOX) gene regulates plant development and growth by affecting the expression of several other genes. In this study, three WOX genes, NnWOX1-1, NnWOX4-3, and NnWOX5-1, were isolated and their functions were assessed in Arabidopsis plants.

Results: The full lengths of NnWOX1-1, NnWOX4-3, and NnWOX5-1 were 1038, 645, and 558 bp, encoding 362, 214, and 185 amino acid residues, respectively. Phylogenetic analysis classified NnWOX1-1 and NnWOX4-3 encoding proteins into one group, and NnWOX5-1 and MnWOX5 encoding proteins exhibited strong genetic relationships. The three genes were induced by sucrose and indoleacetic acid (IAA) and exhibited organ-specific expression characteristics. In addition to improving root growth and salt tolerance, NnWOX1-1 and NnWOX4-3 promoted stem development in transgenic Arabidopsis plants. A total of 751, 594, and 541 genes, including 19, 19, and 13 respective genes related to ethylene and IAA metabolism and responses, were enhanced in NnWOX1-1, NnWOX4-3, and NnWOX5-1 transgenic plants, respectively. Further analysis showed that ethylene production rates in transgenic plants increased, whereas IAA, peroxidase, and lignin content did not significantly change. Exogenous application of ethephon on lotus seedlings promoted AR formation and dramatically increased the fresh and dry weights of the plants.

Conclusions: NnWOX1-1, NnWOX4-3, and NnWOX5-1 influence root formation, stem development, and stress adaptation in transgenic Arabidopsis plants by affecting the transcription of multiple genes. Among these, changes in gene expression involving ethylene metabolism and responses likely critically affect the development of Arabidopsis plants. In addition, ethylene may represent an important factor affecting AR formation in lotus seedlings.