LoBLH6 interacts with LoMYB65 to regulate anther development through feedback regulation of gibberellin synthesis in lily

The homeostasis of gibberellin (GA) is crucial for the normal development of anthers, but its underlying regulatory mechanisms are not clear. The GA-induced v-Myb myeloblastosis viral oncogene homolog (MYB) transcription factor LoMYB65 is involved in anther development. In this study, we screened and identified an interacting protein of LoMYB65, <i>Lilium</i> Oriental Hybrids BEL1-Like Homeodomain6 (LoBLH6). LoBLH6 was localized in both the nucleus and cytoplasm, and it interacted with LoMYB65 through its BELL domain, exhibiting transcriptional repression activity. <i>LoBLH6</i> was continuously expressed during anther development, with particularly high expression in the mid and late stages. <i>In situ</i> hybridization revealed high expression of <i>LoBLH6</i> in the tapetum and microspores, with the same tissue specificity as <i>LoMYB65</i>. Silencing of <i>LoBLH6</i> in lilies resulted in abnormal anther development, reduced pollen, and increased GA content. The application of GA-induced phenotypes in the anthers and pollen of lily that were similar to the silencing of <i>LoBLH6</i>. Further research showed that LoBLH6 directly binds to the promoter of <i>Lilium</i> Oriental Hybrids <i>GA 20-oxidase1</i> (<i>LoGA20ox1</i>) to suppress its expression, and coexpression with LoMYB65 enhances this repression. Additionally, GA treatment enhanced the interaction between LoBLH6 and LoMYB65 and their complex's inhibitory effect on downstream target genes. During the transition from microspores to mature pollen grains in lily anthers, GA levels maintain a steady state, which is disrupted by silencing <i>LoBLH6</i>, leading to abnormal pollen development. Overall, our results reveal that the interaction between LoBLH6 and LoMYB65 regulates anther development through feedback regulation of GA synthesis.