Poster: Protein targeting & vesicular trafficking

Abs # 664: Vacuolar biogenesis in germinating pollen differs from that of sporophytes but nevertheless requires VACUOLESS1 for proper function

Presenter:	Hicks, Glenn R., ghicks@citrus.ucr.edu
Authors	Hicks, Glenn R. (A)   Rojo, Enrique  (A)   Hong, Seho  (A)   Carter, David  (A)   Raikhel, Natasha V. (A)
Affiliations:	(A): Dept of Botany & Plant Sciences and Center for Plant Cell Biology, University of California, Riverside, CA

Vacuoles perform multiple functions and VACUOLESS1 (VCL1) is essential for biogenesis with loss of expression in the vcl1 mutant leading to embryo lethality (Rojo et al, 2001 Dev Cell 1:303-310). VCL1 is a member of a protein complex, the AtC-VPS complex, found at the tonoplast and pre-vacuolar compartment and is likely involved in regulation of membrane fusion (Rojo et al, 2003 Mol Biol Cell 14:361-369). Vacuolar biogenesis is prominent in the development of gametophytes yet is poorly understood. Given the importance of VCL1, we asked if it contributes to vacuolar biogenesis during pollen germination. However, it was essential to first understand the dynamics of vacuoles. A tonoplast marker, δ-TIP::GFP, under a pollen promoter permitted the examination of vacuolar morphology in germinating Arabidopsis pollen. In examining the progression of biogenesis we found that pollen vacuoles are extremely dynamic with remarkable features such as elongated vacuoles and highly mobile cytoplasmic invaginations. Surprisingly, although there are no homologs of VCL1 in Arabidopsis, vcl1 does not appear to impact vacuolar morphology in pollen germinated in vitro. Nevertheless, genetic and other approaches demonstrate reduced transmission of vcl1 through pollen and suggest that vcl1 is expressive after germination. Interestingly, vcl1 affected the fertility of female gametophytes which undergo complex vacuolar biogenesis. Our results point to the complexity of pollen vacuoles and suggest that the mechanism of vacuolar biogenesis in pollen may differ from that of sporophytes (Hicks et al, 2004, Plant Physiol 134:1-13). We will present our recent approaches for understanding the nature of the vcl1 defect in pollen and the role of VCL1 in the mechanism of vacuolar biogenesis.