Arabidopsis Intracellular NHX-Type Sodium-Proton Antiporters are Required for Seed Storage Protein Processing

Abstract

The Arabidopsis intracellular sodium-proton exchanger (NHX) proteins AtNHX5 and AtNHX6 have a well-documented role in plant development, and have been used to improve salt tolerance in a variety of species. Despite evidence that intracellular NHX proteins are important in vacuolar trafficking, the mechanism of this role is poorly understood. Here we show that NHX5 and NHX6 are necessary for processing of the predominant seed storage proteins, and also influence the processing and activity of a vacuolar processing enzyme. Furthermore, we show by yeast two-hybrid and bimolecular fluorescence complementation (BiFC) technology that the C-terminal tail of NHX6 interacts with a component of Retromer, another component of the cell sorting machinery, and that this tail is critical for NHX6 activity. These findings demonstrate that NHX5 and NHX6 are important in processing and activity of vacuolar cargo, and suggest a mechanism by which NHX intracellular (IC)-II antiporters may be involved in subcellular trafficking.

The Role of Na+ and K+ Transporters in Salt Stress Adaptation in Glycophytes

“…Members of the NHX antiporter family have come to be regarded as key players in intracellular Na + /K + and pH homeostasis, growth and development, stomatal functions, protein and vesicle trafficking and tolerance to abiotic stress (Jiang et al, 2010; Huertas et al, 2013; Andrés et al, 2014; Ashnest et al, 2015; Wang L. et al, 2015; Wang et al, 2016; Wu et al, 2016). These regulatory roles result from the Na + (K + )/H + exchange activity of the transporters, whose mode of action has been depicted as an “alternating access” mode (Bassil et al, 2011).…”

AtNHX5 and AtNHX6: Roles in protein transport

“…Retromer is the cellular sorting machinery that recycles VSRs back to the TGN from the PVC. 7 Therefore, these findings suggest that AtNHX5 and AtNHX6 regulate protein transport by controlling the recycling of VSRs. 7 A recent study by Wu et al examined the role of AtNHX5 and AtNHX6 in regulating a SNARE complex and its function in protein trafficking.…”

“…7 Therefore, these findings suggest that AtNHX5 and AtNHX6 regulate protein transport by controlling the recycling of VSRs. 7 A recent study by Wu et al examined the role of AtNHX5 and AtNHX6 in regulating a SNARE complex and its function in protein trafficking. 8 This SNARE complex, which is composed of VAMP727, SYP22, VTI11 and SYP51, is important for protein transport and PSV biogenesis in Arabidopsis.…”

“…5 Ashnest et al confirmed the notion that AtNHX5 and AtNHX6 regulate the transport and processing of seed storage proteins as well as the biogenesis of the PSVs. 7 In addition, they found that nhx5 nhx6 accumulated in the seeds a high level of the 52 kDa precursor of bVPE, a vacuolar processing enzyme. The catalytic activity of bVPE was reduced in nhx5 nhx6.…”

“…[4][5][6] Accumulating evidence indicates that AtNHX5 and AtNHX6 play an important role in protein transport. 5,[7][8][9] AtNHX5 and AtNHX6 have diversified roles in protein transport Reguera et al examined the role of AtNHX5 and AtNHX6 in protein transport. 5 They found that nhx5 nhx6 produced large, heavy seeds with a dark coat.…”