Xylem specific activation of 5’ upstream regulatory region of two NAC transcription factors (MusaVND6 and MusaVND7) in banana is regulated by SNBE-like sites

Deposition of secondary cell wall in the xylem elements is controlled by a subgroup of NAC (NAM, ATAF, CUC) family, known as vascular-related NAC transcription factors (VNDs). In the present study, we analyzed the 5’ upstream regulatory region of two banana NAC transcription factors ( MusaVND6 and MusaVND7 ) for tissue specific expression and presence of 19-bp secondary-wall NAC binding element ( SNBE )-like motifs. Transgenic banana plants of Musa cultivar Rasthali harboring either P MusaVND7 :: GUS or P MusaVND6 :: GUS showed specific GUS (β-D-Glucuronidase) activity in cells of the xylem tissue. Approximately 1.2kb promoter region of either MusaVND6 or MusaVND7 showed presence of at least two SNBE -like motifs. This 1.2kb promoter region was retarded in a gel shift assay by three banana VND protein (VND1,VND2 and VND3). The banana VND1-VND3 could also retard the mobility of isolated SNBE -like motifs of MusaVND6 or MusaVND7 in a gel shift assay. Transcript levels of MusaVND6 and MusaVND7 were elevated in transgenic banana overexpressing either banana VND1 , VND2 or VND3 . Present study suggested a probable regulation of banana VND6 and VND7 expression through direct interaction of banana VND1- VND3 with SNBE -like motifs. Our study also indicated two promoter elements for possible utilization in cell wall modifications in plants especially banana, which is being recently considered as a potential biofuel crop.