Arabidopsis BIG1 and BIG5 are crucial for male gametophyte transmission.

Arabidopsis contains five Brefeldin A-inhibited guanine nucleotide exchange factors (BIGs), which play a critical role in vesicle biogenesis for protein traffic from the Golgi to the plasma membrane. Biological processes regulated by BIG1-BIG4 are postulated to be distinct from those by BIG5. However, we show that the self-pollinated BIG1+/- big5 silique do not produce homozygous seeds, and some pollen tubes from BIG1+/- big5 anthers grew slowly in vitro and failed to target nearby ovules in vivo. We identified the big1 big5 homozygote from the progeny of BIG1+/- big5 plants transformed with BIG5, whose expression is driven by a pollen-specific promoter pLat52, indicating that male gametophyte transmission is blocked in the double mutant. Confocal microscopy indicated that BIG1 and BIG5 are co-localized in the Golgi network. Thus, our data indicate that BIG1 and BIG5 are crucial for male gametophyte transmission.