KIN10-mediated phosphorylation attenuates cooperative repression of oil accumulation by AHL14 and AHL29 in Arabidopsis seeds

In many higher plants, seed oil accumulation is strictly controlled by complex multilevel regulatory networks, among which transcriptional and post-transcriptional regulations are indispensable. In this study, we identified 2 Arabidopsis thaliana AT-HOOK MOTIF NUCLEAR LOCALIZED (AHL) transcription factors, AHL14 and AHL29, which are highly expressed in developing embryos and act as key repressors of oil accumulation in seeds. AHL14 and AHL29 physically interact with each other as well as with themselves. They cooperatively repress seed oil deposition by directly inhibiting the expression of the key fatty acid biosynthesis genes PYRUVATE DEHYDROGENASE-E1 β1 (PDH-E1 β1) and BIOTIN CARBOXYL CARRIER PROTEIN2 (BCCP2), as validated by genetic and enzyme activity analyses. Furthermore, we demonstrated that SUCROSE NON-FERMENTING1-KINASE HOMOLOG10 (KIN10) physically interacts with and phosphorylates AHL14, but not AHL29. This interaction facilitates the proteasomal degradation of AHL14, thereby alleviating its inhibitory effect on PDH-E1 β1 and BCCP2 expression and ultimately attenuating the cooperative repression of oil accumulation by AHL14 and AHL29 in seeds. Additionally, we showed that AHL14 and AHL29 indirectly suppress the expression of the hub transcription factor gene WRINKLED1 (WRI1) during seed oil production, whose protein stability has been previously proven to be negatively regulated by KIN10-mediated phosphorylation. Our findings reveal a KIN10-AHL14-AHL29 module that complements the KIN10-WRI1 pathway in fine-tuning oil production in seeds.