NnDREB2 regulated by NnWOX1-1 is involved in adventitious root formation in lotus root (Nelumbo nucifera Gaertn.)

Lotus root, a crucial aquatic cash crop, demonstrates primary root atrophy, while developing adventitious roots critically mediate nutrient acquisition and product organ development. Previous investigation reveals the functional involvement of NnWOX1-1 in root development through transgenic Arabidopsis models.

In this study, we demonstrated nuclear and membrane co-localization of NnWOX1-1 fluorescence signals in tobacco leaf epidermal cells. NnWOX1-1 overexpression significantly enhanced root elongation and increased root primordia formation in transgenic lotus root and Sagittaria trifolia plants. We identified NnDREB2C as a downstream target gene of NnWOX1-1. The 615 bp nucleotide sequence of NnDREB2C encoded a 205-amino acid polypeptide containing a conserved AP2 domain. Subcellular localization assays revealed exclusive nuclear accumulation of NnDREB2C-GFP fusion proteins in tobacco mesophyll cells. NnDREB2C transcription was significantly upregulated under 200 mg/L ethephon treatment and 20 g/L sucrose exposure, while remaining unresponsive to 10 µM indole-3-acetic acid (IAA). Tissue-specific expression analysis showed maximum transcript abundance in leaves, floral organs, and internodal segments, with minimal expression in fruits and petioles. Transgenic manipulation experiments established that NnDREB2C overexpression enhanced the number and length of adventitious root in both lotus and S. trifolia plants. Conversely, RNAi-mediated knockdown lines exhibited significant reductions in the adventitious root development compared to wild-type counterparts.

Through functional analysis of NnWOX1-1, NnDREB2C and the measurement of ethylene content in transgenic plants, we demonstrated that NnDREB2C regulated by NnWOX1-1 was involved in the formation of adventitious roots in lotus seedling. Additionally, NnWOX1-1 and NnDREB2C affected synthesis of ethylene which was also an important regulator of adventitious roots.