Senescence-associated genes, usually shortened to SAGs, are genes that become more active or less active as a plant organ enters senescence, the genetically controlled aging process that leads to the breakdown and recycling of tissues. In leaves, SAGs help regulate chlorophyll loss, protein and membrane breakdown, nutrient remobilization, and changes in hormone signaling.
In gardening and plant care, SAG activity is part of why older leaves yellow, dry, and eventually die while the plant redirects nitrogen and other nutrients to new growth, storage organs, flowers, fruits, or seeds. Their expression is influenced by age, darkness, drought, pathogens, and plant hormones such as ეთylene, abscisic acid, cytokinins, and jasmonates.
SAGs are not all “death genes.” Some promote tissue breakdown, while others protect cells, manage stress, or control the timing of senescence so the process happens in an orderly way rather than as sudden injury. This distinguishes senescence from damage caused by rot, scorch, or mechanical injury, which can kill tissue without following the same regulated genetic program.
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