Novel flavin-containing monooxygenase protein FMO1 interacts with CAT2 to negatively regulate drought tolerance through ROS homeostasis and ABA signaling pathway in tomato

Abstract

Drought stress is the major abiotic factor that can seriously affect plant growth and crop production. The functions of flavin-containing monooxygenases (FMOs) are known in animals. They add molecular oxygen to lipophilic compounds or produce reactive oxygen species (ROS). However, little information on FMOs in plants is available. Here, we characterized a tomato drought-responsive gene that showed homology to FMO, and it was designated as <i>FMO1</i>. <i>FMO1</i> was downregulated promptly by drought and ABA treatments. Transgenic functional analysis indicated that RNAi suppression of the expression of <i>FMO1</i> (<i>FMO1</i>-Ri) improved drought tolerance relative to wild-type (WT) plants, whereas overexpression of <i>FMO1</i> (<i>FMO1</i>-OE) reduced drought tolerance. The <i>FMO1</i>-Ri plants exhibited lower ABA accumulation, higher levels of antioxidant enzyme activities, and less ROS generation compared with the WT and <i>FMO1</i>-OE plants under drought stress. RNA-seq transcriptional analysis revealed the differential expression levels of many drought-responsive genes that were co-expressed with <i>FMO1</i>, including <i>PP2Cs</i>, <i>PYLs</i>, <i>WRKY</i>, and <i>LEA</i>. Using Y2H screening, we found that <i>FMO1</i> physically interacted with catalase 2 (CAT2), which is an antioxidant enzyme and confers drought resistance. Our findings suggest that tomato <i>FMO1</i> negatively regulates tomato drought tolerance in the ABA-dependent pathway and modulates ROS homeostasis by directly binding to SlCAT2.