Geminating pollen has tubular vacuoles, displays highly dynamic vacuole biogenesis, and requires VACUOLESS1 for proper function.
Vacuoles perform multiple functions in plants, and VCL1 (VACUOLESS1) is essential for biogenesis with loss of expression in the vcl1 mutant leading to lethality. Vacuole biogenesis plays a prominent role in gametophytes, yet is poorly understood. Given the importance of VCL1, we asked if it contributes to vacuole biogenesis during pollen germination. To address this question, it was essential to first understand the dynamics of vacuoles. A tonoplast marker, delta-TIP::GFP, under a pollen-specific promoter permitted the examination of vacuole morphology in germinating pollen of Arabidopsis. Our results demonstrate that germination involves a complex, yet definable, progression of vacuole biogenesis. Pollen vacuoles are extremely dynamic with remarkable features such as elongated (tubular) vacuoles and highly mobile cytoplasmic invaginations. Surprisingly, vcl1 did not adversely impact vacuole morphology in pollen germinated in vitro. To focus further on VCL1 in pollen, reciprocal backcrosses demonstrated reduced transmission of vcl1 through male gametophytes, indicating that vcl1 was expressive after germination. Interestingly, vcl1 affected the fertility of female gametophytes that undergo similarly complex vacuole biogenesis. Our results indicate that vcl1 is lethal in the sporophyte but is not fully expressive in the gametophytes. They also point to the complexity of pollen vacuoles and suggest that the mechanism of vacuole biogenesis in pollen may differ from that in other plant tissues.
Center for Plant Cell Biology and Department of Botany and Plant Sciences, University of California, Riverside, Riverside, California 92521, USA.
Glenn R
GR
Hicks
Enrique
E
Rojo
Seho
S
Hong
David G
DG
Carter
Natasha V
NV
Raikhel
D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology*; D001483:Base Sequence; D018744:DNA, Plant / Q000235:genetics; D017343:Genes, Plant; D017930:Genes, Reporter; D018525:Germination; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics; D030821:Plants, Genetically Modified; D011058:Pollen / Q000502:physiology / Q000648:ultrastructure; D011993:Recombinant Fusion Proteins / Q000235:genetics; D014617:Vacuoles / Q000502:physiology / Q000648:ultrastructure
D029681:Arabidopsis Proteins; D018744:DNA, Plant; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; C440208:VCL1 protein, Arabidopsis; D049452:Green Fluorescent Proteins