LpNOL‐knockdown suppression of heat‐induced leaf senescence in perennial ryegrass involving regulation of amino acid and organic acid metabolism

Abstract The nonyellow COLORING 1‐like gene ( NOL ) is known for its roles in accelerating leaf senescence, but the underlying metabolic mechanisms for heat‐induced leaf senescence remain unclear. The objectives of this study were to identify metabolites and associated metabolic pathways regulated by knockdown of NOL in perennial ryegrass ( Lolium perenne ) and to determine the metabolic mechanisms of NOL controlling heat‐induced leaf senescence. Wild‐type (WT; cv. “Pinnacle”) and two lines (Noli‐1 and Noli‐2) of perennial ryegrass with LpNOL knockdown were exposed to heat stress at 35/33°C (day/night) or nonstress control temperatures at 25/22°C (day/night) for 30 days in growth chambers. Leaf electrolyte leakage, chlorophyll (Chl) content, photochemical efficiency ( F v / F m ), and net photosynthetic rate (Pn) were measured as physiological indicators of leaf senescence, while gas chromatography‐mass spectrometry was performed to identify metabolites regulated by LpNOL . Knockdown of LpNOL suppressed heat‐induced leaf senescence and produced a stay‐green phenotype in perennial ryegrass, as manifested by increased Chl content, photochemical efficiency, net photosynthetic rate, and cell membrane stability in Noli‐1 and Noli‐2. Five metabolites (valine, malic acid, threonic acid, shikimic acid, chlorogenic acid) were uniquely upregulated in LpNOL plants exposed to heat stress, and six metabolites (aspartic acid, glutamic acid, 5‐oxoproline, phenylalanine, proline, tartaric acid) exhibited more pronounced increases in their content in LpNOL plants than the WT. LpNOL could regulate heat‐induced leaf senescence in perennial ryegrass through metabolic reprogramming in the pathways of respiration, secondary metabolism, antioxidant metabolism, and protein synthesis.