The pollen specific LIM gene for pollen germination and pollen tube growth in Arabidopsis thaliana

Pollen germination and pollen tube growth are important process in plant reproduction. LIM proteins are protein family for actin filament dynamics that induces pollen germination and tip growth in pollen tube. In the Arabidopsis thaliana genome, six genes encode LIM domain-containing proteins, and are classified into 3 groups: AtWLIM1, AtWLIM2 and AtPLIM2. Genes in AtWLIM1 and AtWLIM2 groups expressed in whole plant tissues, and, in contrast, genes in AtPLIM2 group expressed specifically in pollen. The AtPLIM2 group includes three genes, AtPLIM2a, AtPLIM2b and AtPLIM2c. AtPLIM2a and AtPLIM2b were reported their biochemical feature and their interaction with action filaments in growing pollen tube, but their knockdown mutants have little effects in pollen germination and pollen tube growth. Thus, the biological function of LIM proteins in pollen tube growth is still not clear. In this study, we focused on AtPLIM2c. First, we constructed RNA interference (RNAi) mutants, and observed their pollen germination and pollen tube growth in vitro and in vivo. The atplim2c RNAi mutants showed delayed pollen germination, compared to wild type Arabidopsis plant. Speed of pollen tube growth was also decreased in the mutants, although pollen tube finally arrived at an embryo sac with an extended period of time. These results suggested that AtPLIM2c is critical for pollen germination and pollen tube growth, and involved in actin filament polymerization in growing pollen tube.