Functional characterisation of the <i>EgPAL5</i> promoter from oil palm (<i>Elaeis guineensis</i> Jacq.) reveals its potential roles in plant growth and adaptation to drought

Oil palm (<i>Elaeis guineensis</i>) is a globally important oil crop whose genome contains five <i>phenylalanine ammonia lyase</i> (<i>EgPAL</i>) genes. In this study, we characterised the regulatory architecture of the <i>EgPAL5</i> promoter by generating transgenic plants carrying the <i>EgPAL5</i> promoter fused to GUS. We first conducted an <i>in silico</i> analysis of the 2.3 kb 5’ flanking region, identifying multiple <i>cis-</i>regulatory motifs involved in monolignol biosynthesis, osmotic stress response, and hormone signalling. Reporter assays under normal growth conditions revealed broad promoter activity throughout the seedling and adult plant, with developmental modulation manifested as higher GUS expression detected in expanding leaves and developing siliques. Under simulated drought stress, GUS activity increased markedly, indicating strong promoter induction. Moreover, overexpression of the Arabidopsis <i>AtMYB58</i> transcription factor significantly enhanced <i>EgPAL5</i> promoter activity, further implying that the <i>EgPAL5</i> promoter was responsive to regulatory cues associated with lignin biosynthesis. Promoter deletion mapping localised essential <i>cis-</i>elements required for full transcriptional activity to the −1033 to −651 bp region upstream of the transcription start site. Together, these results demonstrate that the <i>EgPAL5</i> promoter integrates developmental cues and environmental stimuli to modulate phenylpropanoid metabolism.