The Ca(2+) status of the endoplasmic reticulum is altered by induction of calreticulin expression in transgenic plants.
To investigate the endoplasmic reticulum (ER) Ca(2+) stores in plant cells, we generated tobacco (Nicotiana tabacum; NT1) suspension cells and Arabidopsis plants with altered levels of calreticulin (CRT), an ER-localized Ca(2+)-binding protein. NT1 cells and Arabidopsis plants were transformed with a maize (Zea mays) CRT gene in both sense and antisense orientations under the control of an Arabidopsis heat shock promoter. ER-enriched membrane fractions from NT1 cells were used to examine how altered expression of CRT affects Ca(2+) uptake and release. We found that a 2.5-fold increase in CRT led to a 2-fold increase in ATP-dependent (45)Ca(2+) accumulation in the ER-enriched fraction compared with heat-shocked wild-type controls. Furthermore, after treatment with the Ca(2+) ionophore ionomycin, ER microsomes from NT1 cells overproducing CRT showed a 2-fold increase in the amount of (45)Ca(2+) released, and a 2- to 3-fold increase in the amount of (45)Ca(2+) retained compared with wild type. These data indicate that altering the production of CRT affects the ER Ca(2+) pool. In addition, CRT transgenic Arabidopsis plants were used to determine if altered CRT levels had any physiological effects. We found that the level of CRT in heat shock-induced CRT transgenic plants correlated positively with the retention of chlorophyll when the plants were transferred from Ca(2+)-containing medium to Ca(2+)-depleted medium. Together these data are consistent with the hypothesis that increasing CRT in the ER increases the ER Ca(2+) stores and thereby enhances the survival of plants grown in low Ca(2+) medium.
Persson
S
S
Dpartment of Botany, North Carolina State University, Raleigh, North Carolina 27695-7612, USA.
Wyatt
S E
SE
Love
J
J
Thompson
W F
WF
Robertson
D
D
Boss
W F
WF
D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000096:biosynthesis*; D037282:Calreticulin; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D018869:Heat-Shock Response; D010641:Phenotype; D010940:Plant Proteins / Q000378:metabolism; D030821:Plants, Genetically Modified; D010947:Plants, Toxic; D012261:Ribonucleoproteins / Q000096:biosynthesis*; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism*; D003313:Zea mays / Q000235:genetics / Q000378:metabolism*
D002135:Calcium-Binding Proteins; D037282:Calreticulin; D010940:Plant Proteins; D012261:Ribonucleoproteins; D002118:Calcium