ZmS5H: A MULTI-FUNCTIONAL ENZYME REGULATING PLANT DEVELOPMENT AND SENESCENCE IN MAIZE

PALOMA SERRA; JULIETA PETRICH; SILVANA RIGHINI ARAMBURU; FALCONE FERREYRA, MARÍA LORENA; PAULA CASATI

Congreso; XXXIV Reunión Argentina de Fisiología Vegetal; 2023

Salicylic acid (SA) is a phytohormone that plays a crucial role regulating various aspects of plant life, including disease resistance, leaf senescence, flowering time, and thermogenesis. SA undergoes chemical modifications such as methylation, hydroxylation, or conjugation with sugars or amino acids. SA hydroxylation is catalyzed by enzymes known as SALICYLIC ACID HYDROXYLASES (SHs) and plays an essential role in plant development and response to pathogens. In our lab, we successfully identified the first SA hydroxylase in maize plants, known as salicylic acid 5-hydroxylase (ZmS5H), a 2-oxoglutarate dependent dioxygenase (2-ODD) that catalyzes the conversion of SA into 2,5-dihydroxybenzoic acid (2,5-DHBA) by hydroxylating the C5 position of its phenyl ring. Since some 2-ODD enzymes involved in plant phenolic metabolism can accept various phenolic compounds as substrates, we tested two flavanones (naringenin and eriodictyol) and one dihydroflavonol (dihydroquercetin, DHQ) as putative substrates of ZmS5H. We observed that ZmS5H also exhibits flavonol synthase activity, as it can convert dihydroquercetin (DHQ) into the flavonol quercetin (QUE). To validate the dual functionality of ZmS5H, we quantified SA, 2,5-DHBA, and QUE levels by LC-MS in young maize leaves of wild type (W22) and mutant s5h plants, quantifying reduced levels of both 2,5-DHBA and QUE in the absence of S5H. However, in adult maize leaves, the s5h mutant lines showed an accumulation of QUE. Furthermore, a phenotypic characterization of maize plants indicated that s5h mutant lines exhibited increased senescence and affected plant growth. These findings strongly suggest that ZmS5H adapts its functionality based on the specific needs of each stage of plant development, playing a pivotal role in both plant growth and senescence.