The FRK1 mitogen-activated protein kinase kinase kinase (MAPKKK) from Solanum chacoense is involved in embryo sac and pollen development.

The fertilization-related kinase 1 (ScFRK1), a nuclear-localized mitogen-activated protein kinase kinase kinase (MAPKKK) from the wild potato species Solanum chacoense, belongs to a small group of pMEKKs that do not possess an extended N- or C-terminal regulatory domain. Initially selected based on its highly specific expression profile following fertilization, in situ expression analyses revealed that the ScFRK1 gene is also expressed early on during female gametophyte development in the integument and megaspore mother cell and, later, in the synergid and egg cells of the embryo sac. ScFRK1 mRNAs are also detected in pollen mother cells. Transgenic plants with lower or barely detectable levels of ScFRK1 mRNAs lead to the production of small fruits with severely reduced seed set, resulting from a concomitant decline in the number of normal embryo sacs produced. Megagametogenesis and microgametogenesis were affected, as megaspores did not progress beyond the functional megaspore (FG1) stage and the microspore collapsed around the first pollen mitosis. As for other mutants that affect embryo sac development, pollen tube guidance was severely affected in the ScFRK1 transgenic lines. Gametophyte to sporophyte communication was also affected, as observed from a marked change in the transcriptomic profiles of the sporophytic tissues of the ovule. The ScFRK1 MAPKKK is thus involved in a signalling cascade that regulates both male and female gamete development.

ScORK17, a transmembrane receptor-like kinase predominantly expressed in ovules is involved in seed development.

The mRNA expression of the Solanum chacoense Ovule Receptor Kinase 17 (ScORK17), a receptor kinase of the LRR-VI subfamily, is highly specific to the female reproductive tissues. No LRR-VI subfamily members in any plant species have yet been attributed a function. A phylogenetic tree inferred using the kinase domain of LRR-VI subfamily members separated the family into two clades: one containing an average of 8.2 LRR per protein and a second clade containing an average of 2.7. In situ hybridization analyses showed that the ScORK17 signal was mainly detected in the single ovule integument and in the endothelium. Transient expression analysis also revealed that ScORK17 was N-glycosylated in planta. Overexpression of ScORK17 in S. chacoense did not produce plants with an altered phenotype. However, when heterologous transformation was performed with a full-length ScORK17 clone in A. thaliana, the resulting transgenic plants showed reduced seed set, mainly due to aberrant embryo sac development, thus supporting a developmental role for ScORK17 in ovule and seed development.