%0 Generic
%A Röhrich, Rachel Maria
%C Heidelberg
%D 2024
%F heidok:32714
%R 10.11588/heidok.00032714
%T The V-ATPase at the trans-Golgi network/early endosome during vegetative and reproductive development
%U https://archiv.ub.uni-heidelberg.de/volltextserver/32714/
%X V-ATPases are highly conserved proton pumps that function not only as proton pumps but are involved in many processes through interactions with different proteins. In plant cells, the trans-Golgi network/early endosome (TGN/EE) is a compartment of specific significance, as trafficking pathways converge there. Cargo from secretory, endocytic and recycling trafficking pathways travel through the TGN/EE. Acidification of the TGN/EE is accomplished by V-ATPase complexes with the VHA-a subunit isoform VHA-a1 in Arabidopsis. While V-ATPases which contain VHA-a1 localize to the TGN/EE, V-ATPases with VHA-a2 or VHA-a3 are targeted to the tonoplast, the limiting membrane of the vacuole. This thesis describes the mutant phenotype of the gene encoding the subunit VHA-a1. Strikingly, during vegetative development vha-a1 is wildtype like. It is shown that VHA-a2/VHA-a3-containing V-ATPases can compensate for the lack of VHA-a1 during vegetative growth. Given the subcellular specialization of VHA-a1 versus VHA-a2 and VHA-a3 this is astonishing and represents a striking example of functional redundancy of isoforms despite differential localization. I further show that VHA-a1 is essential for pollen development. VHA-a3-containing V-ATPases are not able to compensate for the lack of VHA-a1 in pollen development. Microspores in the vha-a1 mutant are defective in pollen wall formation. As early as at the tetrad stage, when pollen wall development starts with the formation of the primexine, defects are visible in vha-a1. Rescue experiments with VHA-a1 expressed under the control of different promoters revealed that tapetum-specific expression of VHA-a1 does not rescue pollen development of vha-a1. For the process of primexine formation the results of this work suggest that primexine formation is largely governed by the gametophyte. In addition to the early defect, absence of VHA-a1 leads to a late defect, as seen from the lack of transmission of the mutant allele via the male gametophyte despite at the time of pollen release vha-a1 and wildtype microspores in vha-a1/+ anthers are indistinguishable. Furthermore, the potential capability of pH sensing of the TGN/EE resident V-ATPase in Arabidopsis and the underlying molecular mechanism was analyzed by mutation of VHA-a1 histidine residues. While some VHA-a1 histidine substitution variants were able to rescue the defect in pollen development of vha-a1, others possibly cannot, suggesting that these histidine residues have an essential function. Moreover, this thesis shows that also the V-ATPase-associated VHA-AP1 is essential for the male gametophyte and that its knock-down results in reduced cell expansion.