RELATIONSHIP BETWEEN FLAVONE SYNTHESIS AND SALICYLIC ACID METABOLISM

DILLON, F; CASATI, P; SERRA, P; FALCONE FERREYRA, ML; RIGHINI ARAMBURU, S; GROTEWOLD, E

Congreso; LVI Reunión Anual de SAIB; 2020

One of the main groups of specialized metabolites synthesized in plants corresponds to flavonoids. Depending on chemical variations present in the central backbone of its structure, these molecules are classified into six main groups. Flavones, one of the most important groups, are synthesized by enzymes known as flavone synthases (FNSs). Two distinct FNS enzymes were identified, capable of using equivalent substrates and synthesize the same products by different mechanisms. On one hand, flavone synthase I (FNSI) enzymes belong to a superfamily of soluble Fe+2/2-oxoglutarate-dependent dioxygenases (2-ODDs). The second group of enzymes that catalyze the formation of flavones are flavone synthases II (FNSII), which belongs to a family of NADPH- and oxygen-dependent cytochrome P450 membrane-bound monooxygenases. In the model organism Arabidopsis thaliana, Downey Mildew Resistant 6 (DMR6) encodes an FNSI type enzyme. dmr6 mutant plants show increased resistance against the attack of 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 enzymes from maize. The main goal 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. Preliminary results showed that two of the lines that showed restoration of susceptibility also had decreased 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. We observed that apigenin represses the expression of at least four genes associated with SA metabolism: PATHOGENESIS-RELATED GENE 1 (PR1), PR5, SALICYLIC ACID 5-HIDROXYLASE and ISOCHORISMATE SYNTHASE. Together, our results validate the hypothesis of a possible connection between flavone synthesis and SA metabolism.