Cloning and functional analysis of flavanone 3-hydroxylase gene related to allelopathy in tillered onion

The putative allelochemicals of tillered onion (Allium cepa L. var. multiplicans Baileysyn. var. aggregatum Don) are mainly produced in the phenylpropanoid biosynthesis pathway, inwhich flavanone 3-hydroxylase (F3H) is the key enzyme. A novel cDNA sequence encoding anF3H gene in tillered onion (AcF3H, GenBank: MF805715) was isolated. The open reading frameof AcF3H comprised 1104bp encoding a protein of 367 amino acids with a molecular weight of41.3kD and an isoelectric point of 5.24, according to the ProtParam software. The phylogenetictree of AcF3H showed that the tillered onion protein was closely related to Allium cepa from thesame family, Liliaceae, followed by Lycoris chinensis and Narcissus tazetta var. chinensis.AcF3H was found to contain two conserved motifs: HxDxnH (His220, Asp222 and His278) forbinding FeII and RXS (Arg288) for binding 2-oxoglutarate. To understand the allelopathicpotential of the AcF3H gene, it was over expressed in Arabidopsis thaliana. The contents ofdihydrokaempferol (DHK) and quercetin (Q) were significantly increased in the transgenic A.thaliana over expressing AcF3H by HPLC analysis. The root exudates of transgenic A. thalianastimulated the growth of cucumber radicles, plant height and single-plant fresh weight at lowconcentrations but were inhibitory at high concentrations. Our results first time had provided theidentification of full-length AcF3H gene from tillered onion and it regulates the properaccumulation of flavonoids as antioxidants to promote the growth of cucumber (Cucumis sativusL.) seedlings.