The late pollen actins are essential for normal male and female development in Arabidopsis

In angiosperms the late pollen actins (LPAs) are strongly expressed in mature pollen and pollen tubes and at much lower levels in ovules. Four Arabidopsis lines with homozygous knockout mutations in the four individual LPA genes displayed normal flowers, pollen, and seed set. However, when all four LPAs were silenced simultaneously with a single RNA interference (RNAi) construct targeting the 3'UTR of each mRNA, obvious reproductive defects were observed. Western analysis of various Late Pollen actin RNA interference (LPRi) epialleles showed total LPA protein and RNA expression levels were knocked down from 0% to 95% compared to wild-type levels. Reciprocal crosses with the RNAi lines demonstrated that lowered LPA expression was associated with defects in both male and female fertility. Strong epialleles showed significant reductions in normal silique and seed production and were nearly sterile. Dissection of the siliques from moderate LPRi epialleles revealed many unfertilized ovules, increased numbers of aborted seeds, and decreased numbers of healthy seeds. Microscopic analysis of LPRi pollen indicated that the pollen shape and size were normal, but pollen germinated poorly. While multiple LPA genes may have some functional redundancy, the combined expression of multiple LPA genes appears essential to normal male and female reproductive development.