A Reciprocal Feedback Loop Between Growth-Regulating Factor 9 and SNF1-Related Protein Kinase 1 Integrates Shade Signaling with Autophagy-Mediated Flower Bud Abortion in Lotus

Precise regulation of reproductive growth is vital for plant reproductive success and resource management. Here, we characterize Growth Regulating Factor 9 (NnGRF9), an atypical 14-3-3 family protein in lotus (Nelumbo nucifera), and demonstrate its positive role in shade-induced flower bud abortion. Overexpression of NnGRF9 increases, while silencing reduces, bud abortion, with evidence suggesting that NnGRF9 promotes autophagy during this process. We further identified a reciprocal regulatory loop between NnGRF9 and the energy sensor kinase NnSnRK1, in which NnGRF9 promotes NnSnRK1 expression and activity, whereas NnSnRK1 interacts with NnGRF9 and may regulate its stability. Functional hierarchy analysis places NnGRF9 upstream of NnSnRK1 in regulating both bud abortion and autophagy. NnSnRK1 directly interacts with NnATG6, but not with NnATG1, and manipulation of NnATG6 expression demonstrates that it functions downstream in the regulation of both autophagy and bud abortion. Population genetic analysis reveals that NnGRF9 has been subject to positive selection during lotus evolution, with its allelic variation correlating with differences in flowering abundance among cultivars. In summary, this study elucidates an NnGRF9-NnSnRK1-NnATG6 regulatory pathway that connects shade stress to reproductive fate, and provides population genetic evidence for its role in lotus adaptation and domestication.