TcPHYLL, a cacao phylloplanin expressed in young tissues and glandular trichomes

Abstract

Phylloplanins are potential antimicrobial compounds that can be found on the surface of some plants. These compounds were initially identified in Nicotiana tabacum as proteins secreted by short glandular trichomes (STG), which play an important role in controlling infection caused by Peronospora tabacina, especially by acting on the phylloplane, the first site of plant-pathogen interaction. A protein similar to phylloplanins, containing an Ole e 1 domain, was identified in the Theobroma cacao genome database. In this study, we analyzed the Open Read Frame (ORF) and the promoter of T. Cacao phylloplanin (Tcphyll) using bioinformatics tools, the expression pattern of its transcript by RT-qPCR and the promoter activity driving the β-glucuronidase (GUS) expression in transgenic tobacco. The results indicate that Tcphyll encodes a protein of 158 amino acid residues, with signal peptide and potential glycosylation and phosphorylation sites, which are grouped with phylloplanins instead of allergenic pollen grain proteins. Lower levels of Tcphyll transcripts were found in flowers, and higher levels were found in shoot apical meristem, 2–3 cm segment with leaf primordia and, rich in glandular trichomes. Accumulation of transcripts in meristems increased on the first day after inoculation with Moniliophthora perniciosa, and it was reduced after the second day. Promoter analysis identified 40 cis-acting regulatory elements; the GUS expression, under the control of 731 base pairs of the Tcphyll promoter, was observed in tall and short glandular trichomes. The results indicate that TcPHYLL is the first characterized phylloplanin from a perennial tree.