Phosphorylation of soybean nodulin 26 on serine 262 enhances water permeability and is regulated developmentally and by osmotic signals.
Soybean nodulin 26 is expressed and targeted to the symbiosome membrane of nitrogen-fixing nodules, where it forms an aquaporin channel with a modest water transport rate. In this study, we show that the phosphorylation of nodulin 26 on Ser-262, which is catalyzed by a symbiosome membrane-associated calcium-dependent protein kinase, stimulates its intrinsic water transport rate. Furthermore, using a phosphospecific antibody, we have elucidated the developmental appearance and regulation of nodulin 26 phosphorylation in vivo. Although nodulin 26 protein is detected first in differentiating infected cells (16 days), phosphorylated nodulin 26 does not become pronounced until infected cell maturation (25 days). Phosphorylation is sustained at steady state levels until entry into senescence. Nodulin 26 phosphorylation is enhanced further by osmotic stresses (water deprivation and salinity). Thus, the phosphorylation of nodulin 26 coincides with the establishment of mature nitrogen-fixing symbiosomes, is regulated by osmotic stresses that induce calcium-signaling pathways, and appears to be part of the adaptive responses of infected cells to osmotic challenge.
Guenther
James F
JF
Department of Biochemistry and Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee 37996, USA.
Chanmanivone
Nouth
N
Galetovic
Manker P
MP
Wallace
Ian S
IS
Cobb
Jennifer A
JA
Roberts
Daniel M
DM
D000818:Animals; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology*; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D008565:Membrane Proteins / Q000378:metabolism*; D009154:Mutation; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D009997:Osmotic Pressure; D010766:Phosphorylation; D010940:Plant Proteins / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D013025:Glycine max / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D013559:Symbiosis / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D014867:Water / Q000378:metabolism* / Q000494:pharmacology; D014982:Xenopus laevis / Q000235:genetics / Q000378:metabolism
D008565:Membrane Proteins; D010940:Plant Proteins; C045625:nodulin; D014867:Water; D012694:Serine