Identification and characterization of ZmS5H: Elucidation of its role in biotic stress response

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

Mendoza

Congreso; LVIII Reunión anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular; 2022

Salicylic acid (SA) is a phytohormone that regulates multiple aspects of plant life, including disease resistance, leaf senescence, flowering, and thermogenesis. Levels of salicylic acid are regulated not only by activation of its biosynthetic pathway, but also through its modification by metabolic modifications, such as glycosylation, methylation, amino acid conjugation and hydroxylation. SA can be hydroxylated to 2,3-dihydroxybenzoic acid (2,3-DHBA) or 2,5-dihydroxybenzoic acid (2,5-DHBA), being these hydroxylated acids the major degradation products of SA. The reaction is catalyzed by enzymes known as SALICILYC ACID HYDROXYLASES (SHs). In this study, we report the characterization of the first SA hydroxylase in maize plants: salicylic acid 5-hydroxylase (ZmS5H), a 2-oxoglutarate dependent dioxygenase that catalyzes the formation of 2,5-DHBA by hydroxylating SA at the C5 position of its phenyl ring. Unlike other ZmS5Hs reported in rice and Arabidopsis thaliana, this enzyme does not show substrate inhibition. We also demonstrate that maize mutant plants in S5H accumulate SA. Next, we studied the role of S5H in the susceptibility against the infection with the fungal pathogen Colletotrichum graminiciola. s5h maize mutant plants exhibited less susceptibility against the pathogen attack compared to wild type plants (W22 ecotype) without showing any growth penalty. Moreover, the expression of genes associated with the development of the immune response mediated by SA,including PATHOGENESIS RELATED 1 and 5 and MITOGEN-ACTIVATED KINASE PROTEIN 1 was induced in s5h plants after the infection. We also performed infection experiments in transgenic Arabidopsis thaliana lines expressing ZmS5H in both dmr6 and s3h mutant backgrounds. DOWNY MILDEW RESISTANCE 6 (DMR6) and SALICYLIC ACID HYDROXYLASE 3 (S3H) catalyze the conversion of the flavanone naringenin to the flavone apigenin and SA to 2,3-DHBA, respectively. It is also reported that AtDMR6 has also salicylic acid 5-hydroxylase activity. dmr6 and s3h mutant plants accumulate SA, displaying less susceptibility against pathogen attack. However, when ZmS5H is expressed in either of the Arabidopsis mutants, susceptibility against Pseudomonas syringae was restored. Together, these results provide evidence that ZmS5H has an important role during defense responses in maize plants