Molecular cloning, expression and sequence analysis of a phenylalanine ammonia-lyase gene from Poncirus trifoliata under iron deficiency

Abstract

Phenylalanine ammonia-lyase (PAL) is a specific branch point enzyme of primary and secondary metabolism. It is deemed to play a key role in plant development and defence. Homology cloning of the cDNA sequence of PAL gene, Pt-PAL1, from Poncirus trifoliata found a complete open reading frame (ORF) of 2166 bp, with 721 encoded amino acids. The sequence alignment indicated that the amino acid sequence of Pt-PAL1 shared a high identity with PAL genes found in other plants. Both the dominant and catalytic active sites of Pt-PAL1 were similar to PAL proteins observed in Petroselinum crispum. Phylogenetic tree analysis indicated that Pt-PAL1 was more closely related to PALs in Citrus clementina × C. reticulata than to those from other plants. Real-time polymerase chain reaction showed that the expression of Pt-PAL1 gene in roots under iron (Fe) deficiency (0 μM o,o-FeEDDHA) was significantly higher than that under Fe sufficiency (50 μM o,o-FeEDDHA). The same result was noted for total phenolic content. Phenolic compounds play an important role in response to iron deficiency in Strategy I plants. In the present study, root exudates of Poncirus trifoliata strongly promoted the reutilisation of apoplastic Fe in roots. Furthermore, more Fe was desorbed from the cell wall under Fe deficiency than during Fe sufficiency, indicating a relationship between Fe and total phenolics in Strategy I plants under Fe deficiency.