The ScFRK2 Mitogen-activated Protein Kinase Kinase Kinase (MAP3K) is Involved in Early Embryo Sac Development in

Fertilization-related kinase (FRK) is a group of the mitogen-activated protein kinase kinase kinase (MAP3K or MEKK) that has proliferated in species. Studies on the wild potato have shown that three ScFRKs are directly involved in female gametophyte development. Decreasing the expression of and by RNA interference lead to embryonic sac development arrest at the functional megaspore (FM) stage. As for , the first FRK studied, antisense and co-suppression lines showed no abnormality, while overexpression lines lead to a drastic decrease in seed numbers, presumably caused by a conversion of the ovule into a carpel-like structure. Here we show that in overexpression lines, carpel-like structures from the ovule cannot explain the drastic decrease in seeds considering the low percentage of these carpel-like structures but occurs in early ovule development as observed in and knockdown mutants were most ovules are arrested at the FM stage. The highly similar phenotype from knockdown mutants ( and ) and overexpression lines suggests that these MAP kinases could operate antagonistically through a balance between and on one side and on the other. This study strongly suggests the importance of the FRK family expression levels during early stages of ovule development in embryo sac.