Flavone synthesis and its connection with salicylic acid metabolism in maize plants

SERRA, PALOMA; RIGHINI, S; DILLON, FRANCISCO; FALCONE FERREYRA, MARÍA LORENA; GROTEWOLD, E; CASATI, PAULA

Congreso; 63rd Annual Maize Genetics Conference; 2021

Flavonoids are one of the main groups of specialized metabolites in plants. Flavones, one of the most important flavonoids, are synthesized by enzymes known as flavone synthases (FNSs). There are two different types of FNS enzymes, flavone synthase I (FNSI) enzymes are soluble Fe+2/2-oxoglutarate-dependent dioxygenases; while flavone synthases II (FNSII) belong to a family of NADPH- and oxygen-dependent cytochrome P450 membrane-bound monooxygenases. In Arabidopsis thaliana, Downey Mildew Resistant 6 (DMR6) encodes an FNSI enzyme. dmr6 mutants show increased resistance against the multiple pathogens, including Pseudomonas syringae. This particular phenotype can be associated to an accumulation of the hormone salicylic acid (SA) in dmr6 mutants. Furthermore, there is a restoration of susceptibility to the pathogen attack when dmr6 plants are complemented with FNS I and II from maize. The aim of this work is to study the possible interconnection between flavone synthesis and salicylic acid metabolism. Thus, we analyzed the susceptibility against the attack of the pathogen Pseudomonas syringae in Arabidopsis wild type (Col-0 ecotype) and mutant plants in SALICYLIC ACID 3-HIDROXYLASE (S3H) gene. Salicylic acid 3-hydroxylase enzyme catalyzes the conversion of salicylic acid to 2,3-dihydrobenzoic acid. Therefore, s3h mutants accumulate higher levels of salicylic acid that results in enhanced resistance to infection by pathogens. The infection experiments were also carried out in s3h mutant plants expressing FNS I and II enzymes from maize. Transgenic lines exhibited restoration of susceptibility to Pseudomonas infection. We also quantified the level of salicylic acid in transgenic lines post-infection. Results show that expression of either ZmFNSI or II restore pathogen susceptibility and also increase SA levels. In addition, we analyzed the possible regulatory effect of the flavone apigenin on the expression of genes associated with SA metabolism using RT-qPCR. Together, our results suggest that there is a connection between flavone synthesis and SA metabolism.