The NtBAG5-CaM complex integrates Ca2+ signals to regulate leaf senescence via the antioxidant system in tobacco.

Leaf yellowing critically impacts tobacco quality and economic value. The Bcl-2-associated athanogene (BAG) gene family regulates plant development and senescence, yet the role of NtBAG5 in tobacco remains poorly understood. Here, we demonstrate that NtBAG5 acts as a key promoter of leaf senescence. CRISPR/Cas9-generated NtBAG5 mutants exhibited delayed senescence, enhanced activities of antioxidant enzymes, and reduced malondialdehyde (MDA) content, whereas NtBAG5-overexpressing plants showed the opposite effects. Promoter-GUS analysis revealed high NtBAG5 expression in roots and stems. Hormone treatments indicated that NtBAG5 expression is upregulated by ABA, ETH, IAA, and GA (at late stage) but downregulated by MeJA. Mechanistically, NtBAG5 interacts with calmodulin (CaM) via its BAG domain and IQ motif, as confirmed by yeast two-hybrid and BiFC assays. Ca2 + was found to modulate CaM conformation and strengthen the NtBAG5-CaM interaction. Silencing NtCaM via VIGS induced severe leaf yellowing and growth defects. Our results reveal that the NtBAG5-CaM complex, regulated by Ca2 + and hormones, modulates leaf senescence through the antioxidant system, providing new insights for improving tobacco quality.