Molecular Mechanisms Controlling Ovule Development By Receptor Kinases ODKs In Arabidopsis Thaliana

Receptor-like kinases (RLKs) exist on the plasma membrane and play key roles in cell-to-cell and cell-to-environment communications. In the model plant Arabidopsis, there are at least610members of RLKs. Among them leucine-rich repeat receptor-like kinases (LRR-RLKs) form the largest family. Based on the structures and numbers of the extracellular LRR, LRR-RLKs were classified into13subfamilies. Four members of one LRR-RLK subfamily were found to control redundantly the development of Arabidopsis ovule, and were therefore named the Ovule Development Receptor Kinases (ODKs). In higher plants, ovule is an important organ that will form seed after fertilization. Ovule has both vegetative and reproductive organ characteristics, composed of funiculus, inner and outer integuments, nucellus and embryo sac that is the female gametophyte. In this study, the molecular mechanisms controlling Arabidopsis ovule development by ODKs were investigated with microscopic observations, expression pattern analyses, approaches of genetics and molecular biology. Microscopic observations revealed that the ovules failed to develop at the stage of integument extension in the odkl odk2odk3mutants, resulting in female sterility, a similar phenotype displayed by some known brassinosteroid mutants, er and mpk6mpk3/+mutants. Expression analyses showed that ODK1, ODK2, ODK3are expressed in ovule, a similar expression pattern displayed by ER, ERL1, ERL2, YODA, MKK4, MPK3, and MPK6. Triple or quadruple mutants constructed with er, mpk6and odkl odk3mutants showed phenotypes similar to odk1odk2odk3mutant. Yeast two hybrid experiments further revealed interactions between ODK1, ODK2, ODK3and ER, ERL1, ERL2. The current data support a hypothysis that ODKs regulate Arabidopsis ovule development through the ER and MAPK signaling pathways, and the BR signaling pathway also plays a role in this process.