TCP8 transcription factor negatively regulates Arabidopsis seed germination and antagonizes the function of TCP14

Abstract Teosinte Branched 1/Cycloidea/proliferating cell factors (TCPs) are plant-specific transcription factors that regulate key plant biological processes. So far, only TCP14/TCP15, two members of TCP Class I subfamily, have been characterized as positive regulators of seed germination. In this study, we evidenced that Class I TCP8 negatively regulates seed germination in Arabidopsis. The tcp8.1 mutant seeds exhibited a weaker primary dormancy together with altered expressions of ABA and GA-related genes. Transcriptomic analyses identified 270 genes associated with seed dormancy and germination, differentially expressed in 24h-imbibed tcp8.1 seeds. Strikingly, genes preferentially expressed in the endosperm were overrepresented in tcp8.1 DEGs. Moreover, the germination phenotypes of tcp8.1 and tcp14.4 seeds were abolished in tcp8.1tcp14.4 double mutant, indicating that TCP14 and TCP8 have antagonistic functions. As reported for TCP14, TCP8 interacted with and was phosphorylated by the MAP kinase MPK8. Knocking out MPK8 in tcp8.1, tcp14.4 and tcp8.1tcp14.4 backgrounds did not modify the phenotypes of the corresponding tcp mutants suggesting that MPK8 functions upstream of TCP8 and TCP14. As a whole this study identified a new regulator of germination capacity and shed light on opposite functions for TCP8 and TCP14 in this process that may be coordinated by MPK8.