Flavone Biosynthesis and salicylic acid hydroxylation in maize

RIGHINI, S; EMILIANI, J; RODRIGUEZ, E.; GROTEWOLD, E; CASATI, P.; FALCONE FERREYRA, M.L.

Rosario

Taller; Taller de Biología Molecular de Plantas y sus Aplicaciones Biotecnológicas; 2018

CEFOBI (CONICET-UNR)/IBR(CONICET-UNR)/IICAR (CONICET-UNR)

Salicylic acid (SA) plays roles both in plant physiological responses and defense. Although much research has been carried out on SA biosynthesis, some aspects of its catabolism remain unknown. Recently, a salicylic-3-hydroxylase, a 2- oxoglutarate dependent dioxygenase (2ODD), was characterized in Arabidopsis thaliana (AtS3H). In vivo, this enzyme converts SA to 2,3dihydroxybenzoic acid. In order to study this enzyme in maize, we searched for putative 2-ODD enzymes in the maize genome based on sequence homology. We identified one putative gene encoding a S3H, and its protein sequence was used in phylogenetic reconstructions with several other plant 2-ODD proteins, primarily involved in phenolic metabolism. The tree showed different clusters; and because the putative ZmS3H grouped with the characterized AtS3H, we aimed to demonstrate that the identified gene encoded a S3H enzyme. First, to determine its activity in planta, we generated A. thaliana transgenic plants expressing ZmS3H in the s3h background (mutants in the S3H gene). Then, we investigated the role of the putitative ZmS3H in pathogen infection responses by infection of three independent transgenic lines with P. syringaepv tomato DC3000. Transgenic plants were more susceptible to the pathogen infection than Wild Type Col-0 plants, suggesting that these plants would have decreased SA levels due to higher hydroxylation of it, supporting ZmS3H activity in planta. Moreover, to characterize ZmS3H activity, we cloned the ZmS3H coding region and expressed it in E. coli for further in vivo activity assays. We are testing its activity by feeding SA as substrate followed by the identification of products by HPLC