The STT3a Subunit Isoform of the Arabidopsis Oligosaccharyltransferase Controls Adaptive Responses to Salt/Osmotic Stress

Abstract

Arabidopsis stt3a-1 and stt3a-2 mutations cause NaCl/osmotic sensitivity that is characterized by reduced cell division in the root meristem. Sequence comparison of the STT3a gene identified a yeast ortholog, STT3 , which encodes an essential subunit of the oligosaccharyltransferase complex that is involved in protein N -glycosylation. NaCl induces the unfolded protein response in the endoplasmic reticulum (ER) and cell cycle arrest in root tip cells of stt3a seedlings, as determined by expression profiling of ER stress-responsive chaperone ( BiP -GUS ) and cell division ( CycB1;1 -GUS ) genes, respectively. Together, these results indicate that plant salt stress adaptation involves ER stress signal regulation of cell cycle progression. Interestingly, a mutation ( stt3b-1 ) in another Arabidopsis STT3 isogene ( STT3b ) does not cause NaCl sensitivity. However, the stt3a-1 stt3b-1 double mutation is gametophytic lethal. Apparently, STT3a and STT3b have overlapping and essential functions in plant growth and developmental processes, but the pivotal and specific protein glycosylation that is a necessary for recovery from the unfolded protein response and for cell cycle progression during salt/osmotic stress recovery is associated uniquely with the function of the STT3a isoform.

Specialized Roles of the Conserved Subunit OST3/6 of the Oligosaccharyltransferase Complex in Innate Immunity and Tolerance to Abiotic Stresses

“…In contrast, STT3B deficiency does not lead to an obvious underglycosylation defect, and EFR function is not compromised (Koiwa et al, 2003;Nekrasov et al, 2009;Häweker et al, 2010). However, Arabidopsis stt3a stt3b double knockout plants are gametophytic lethal (Koiwa et al, 2003). These findings highlight the importance of the catalytic OST subunit for protein glycosylation in plants and show that the two putative catalytic subunits have partially overlapping as well as substrate-specific functions.…”

“…In Arabidopsis (Arabidopsis thaliana), two proteins, termed STT3A and STT3B, with homology to the yeast and mammalian catalytic subunits have been identified (Koiwa et al, 2003). STT3A-deficient plants are viable but display a protein underglycosylation defect that affects the biogenesis of heavily glycosylated proteins, such as the pattern recognition receptor EF-TU RECEPTOR (EFR; Nekrasov et al, 2009;Saijo et al, 2009;Häweker et al, 2010).…”

“…STT3A-deficient plants are viable but display a protein underglycosylation defect that affects the biogenesis of heavily glycosylated proteins, such as the pattern recognition receptor EF-TU RECEPTOR (EFR; Nekrasov et al, 2009;Saijo et al, 2009;Häweker et al, 2010). In contrast, STT3B deficiency does not lead to an obvious underglycosylation defect, and EFR function is not compromised (Koiwa et al, 2003;Nekrasov et al, 2009;Häweker et al, 2010). However, Arabidopsis stt3a stt3b double knockout plants are gametophytic lethal (Koiwa et al, 2003).…”

Emerging role of ER quality control in plant cell signal perception

“…The STT3A and STT3B are subunit isoforms of the Arabidopsis oligosaccharyltransferase involved in protein glycosylation. Loss of both STT3A and STT3A resulted in gametophyte developmental defect (Koiwa et al, 2003), suggesting they are important for gametophyte development. The N-glycosylation of EFR by STT3A in the ER plays a key role for its accumulation and ligand recognition during plantpathogen interaction at the plasma membrane.…”

“…In addition, shd pollen tubes fail to elongate in the styles which indicates shd also affects the formation of another protein, receptor or complex required for pollen tube growth in the style. Although the molecular mechanism of STT3A and STT3B is still unclear, it is conceivable that the maturation of a receptor or secretory signal factor essential for the gametophyte development is dependent on these two chaperones (Koiwa et al, 2003). The disulfide isomerase PDIL2-1 has been shown to be involved in embryo sac development (Wang et al, 2008).…”