AFP2 as the novel regulator breaks high-temperature-induced seeds secondary dormancy through ABI5 and SOM in Arabidopsis thaliana.

Imbibed seeds monitor environmental and endogenous signals to break dormancy and initiate growth under appropriate conditions. In Arabidopsis thaliana, high temperature (HT) induces secondary seed dormancy, but the underlying mechanism remains unclear. In this study, we found that the abi5-1 mutant was insensitive to high temperature, whereas plants overexpressing ABI5 displayed sensitivity. We then identified ABA-insensitive five-binding protein 2 (AFP2), which interacts with ABI5 and is involved in HT-induced secondary seed dormancy. Under HT stress, the loss-of-function afp2 mutant showed lower seeds germination frequency, reversely, AFP2 overexpressing lines (OE-AFP2) showed high germination frequency. Similar to the abi5 mutant, the crossed OE-AFP2 abi5 or afp2 abi5 lines showed high germination under HT, suggesting that ABI5 is epistatic to AFP2. SOM is reported to negatively regulate seeds germination by altering GA/ABA metabolism, here we found that AFP2 and ABI5 altered SOM transcription. Specifically, overexpressing AFP2 suppressed SOM transcription, resulting in high expression of GA biosynthesis-related genes and low expression of ABA biosynthesis-related genes, ultimately promoting seed germination under HT. Thus, our data demonstrate that AFP2 is a novel regulator to control HT-induced secondary seed dormancy through ABI5 and SOM.