Oroxylum indicum subsp. root, (L.) Kurz

Deshmukh, Aaditi B., Datir, Sagar S., Bhonde, Yogesh, Kelkar, Natasha, Samdani, Pawan & Tamhane, Vaijayanti A., 2018, De novo root transcriptome of a medicinally important rare tree Oroxylum indicum for characterization of the flavonoid biosynthesis pathway, Phytochemistry 156, pp. 201-213 : 205

2.6. Transcription factor analysis in the O. indicum root transcriptome

At least six distinct transcription factors (TFs) namely myeloblastosis (MYB), basic helix-loop-helix (bHLH), WD or beta-transducin repeat (WD40), WRKY, Zinc finger and MADS box proteins are involved in flavonoid biosynthesis regulation (Terrier et al., 2009). Of these, three transcription factors MYB, bHLH and WD40 (MBW) were detected in the root transcriptome of O. indicum ( Table 6 ; Supplementary Table 3 ). MYB11, MYB12 and MYB111 are known to control flavonol biosynthesis by activating the early biosynthetic steps ( Nesi et al., 2002; Gou et al., 2011), while the MBW complex activates the late biosynthetic genes of flavonoid biosynthesis ( Mehrtens et al., 2005; Stracke et al., 2007; Li, 2014). In the O. indicum root, the MYB transcription factor family was represented prominently, followed by WD40 and bHLH ( Table 6 ; Supplementary Table 3 ). These transcription factors can either work individually or synergistically in controlling the multiple enzymatic steps involved in the flavonoid biosynthesis ( Mano et al., 2007; Hichri et al., 2011).

Among the MYB family TFs, MYB 4 and R2R3-MYB were highly abundant in O. indicum root ( Table 6 ). R2R3-MYB protein is known to participate in the regulation of specialized metabolism including production of phenylpropanoids and flavonoids in plants (Vom Endt et al., 2002; Bomal et al., 2008; Taylor and Grotewold, 2005). The putative TF bHLH was highly expressed in the root transcriptome of O. indicum . bHLH interacts with R3 repeat domains of MYB proteins at the Nterminal acidic region to form the MYB –bHLH complex, involved in flavonoid biosynthesis pathway regulation ( Feller et al., 2011). Transducin/WD-40 family isoform 5, of the WD40 family was abundant in O. indicum roots. WD40 proteins do not possess any catalytic activity, but it has been hypothesized that they act as a docking platform for regulating the anthocyanin and phenylalanine biosynthesis pathways ( Feller et al., 2011).