AtNHX5 and AtNHX6: Roles in protein transport

Abstract

AtNHX5 and AtNHX6, endosomal Na(+),K(+)/H(+) antiporters in Arabidopsis, are localized in the Golgi, trans-Golgi network, and prevacuolear compartment. It becomes evident that AtNHX5 and AtNHX6 play an important role in protein transport toward the vacuole. Studies have shown that AtNHX5 and AtNHX6 regulate the transport of seed storage proteins as well as the biogenesis of the protein storage vacuoles. Three distinct mechanisms have been revealed for the roles of AtNHX5 and AtNHX6 in protein transport. AtNHX5 and AtNHX6 control: (i) the binding of VSR to its cargoes; (ii) the recycling of VSRs; and (iii) subcellular localization of the SNARE complex. Moreover, it has been found that the endosomal pH homeostasis maintained by AtNHX5 and AtNHX6 is critical for the transport of seed storage proteins. Taken together, AtNHX5 and AtNHX6 regulate the trafficking of seed storage proteins into the vacuole; the H(+) leak pathway conducted by AtNHX5 and AtNHX6 is critical for protein transport.

Keywords: Arabidopsis; AtNHX5 and AtNHX6; H+ leak pathway; K+/H+ antiporters; endosomal Na+; pH homeostasis; protein transport.

Figure 1.

A schematic model for the roles of AtNHX5 and AtNHX6 in protein transport into the vacuole. Three distinct mechanisms have been revealed. AtNHX5 and AtNHX6 control: (i) the binding of VSR to its cargoes; (ii) the recycling of VSRs; and (iii) subcellular localization of the SNARE complex. TGN, trans-Golgi network; PVC, prevacuolear compartment; MVB, multivesicular body; PSV, protein storage vacuole; VSR, vacuolar sorting receptor.