Autophagy protein 6 (ATG6) is required for pollen germination in Arabidopsis thaliana

Autophagy is an intracellular recycling pathway that extends the life of an organism in hostile growth conditions. Yeast autophagy protein 6 (Atg6Nps30) is required for formation of autophagosomes during starvation. Here we show that the Arabidopsis ATG6 homolog is an essential gene required for pollen germination and plant development. Analysis of multiple atg6 lines of Arabidopsis containing T-DNA inserts indicated that the homozygous atg6 plants were never recovered and heterozygous plants displayed variable growth phenotypes. atg6 heterozygous pollen test crosses confirmed that a male gametophyte defect was responsible for the loss of homozygous segregants. PCR performed on the pollen samples showed that the T-DNA was present, suggesting the defect occurs after microsporogenesis. Furthermore, plants homozygous for qrtl((-/-)) and heterozygous for atg6- produced tetrads that were trinucleate and stained uniformly with Alexander stain. qrt1((-/-))/ atg6((+/-)) pollen grains exhibited greatly decreased germination efficiencies in vitro. In addition, defective pollen grains were positive for GUS activity (encoded by the insertional T-DNA) indicating that they were the atg6(-) segregants. Finally, a series of in vivo pollen tube guidance experiments suggested no additional pollen defects during pollen tube growth or guidance. Whether ATG6 acts in an autophagy-dependent or independent manner during pollen development, these data suggest novel connections between plant stress responses and reproductive biology.