P-690 - Singlet Oxygen Signaling and Fatty Acid Desaturation in the Chloroplast Interact to Modulate Plant Growth and Defense

The chloroplast regulates photosynthesis, growth, and defense through multiple pathways, including reactive oxygen species (ROS) signaling and modulation of lipid metabolism.  Singlet oxygen (¹O₂) is a potent stress-responsive ROS generated in the chloroplast that can reprogram nuclear gene expression through the EXECUTER (EX) retrograde signaling pathway.  FATTY ACID DESATURASE 7 (FAD7) is a chloroplast-localized membrane desaturase that also influences stress adaptation, promoting resistance to certain stresses such as chilling but increasing susceptibility to others such as aphid attack.  Here, we demonstrate that ¹O₂-responsive retrograde signaling inhibits aphid infestation on Arabidopsis, whereas FAD7 downregulates EX-dependent aphid resistance, possibly by influencing plastoquinone redox status. Furthermore, FAD7 and EX-dependent ¹O₂ signaling interact to influence chlorophyll content, vegetative growth, and flowering time.  These findings reveal a novel linkage between lipid metabolism and reactive oxygen species signaling in the chloroplast and demonstrate new roles for FAD7 and ¹O₂ in regulating the balance between photosynthesis, growth, and defense.