Expression of the high capacity calcium-binding domain of calreticulin increases bioavailable calcium stores in plants

Transgenic Res. 2002 Feb;11(1):1-10. doi: 10.1023/a:1013917701701.

Abstract

Modulation of cytosolic calcium levels in both plants and animals is achieved by a system of Ca2+-transport and storage pathways that include Ca2+ buffering proteins in the lumen of intracellular compartments. To date, most research has focused on the role of transporters in regulating cytosolic calcium. We used a reverse genetics approach to modulate calcium stores in the lumen of the endoplasmic reticulum. Our goals were two-fold: to use the low affinity, high capacity Ca2+ binding characteristics of the C-domain of calreticulin to selectively increase Ca2+ storage in the endoplasmic reticulum, and to determine if those alterations affected plant physiological responses to stress. The C-domain of calreticulin is a highly acidic region that binds 20-50 moles of Ca2+ per mole of protein and has been shown to be the major site of Ca2+ storage within the endoplasmic reticulum of plant cells. A 377-bp fragment encoding the C-domain and ER retention signal from the maize calreticulin gene was fused to a gene for the green fluorescent protein and expressed in Arabidopsis under the control of a heat shock promoter. Following induction on normal medium, the C-domain transformants showed delayed loss of chlorophyll after transfer to calcium depleted medium when compared to seedlings transformed with green fluorescent protein alone. Total calcium measurements showed a 9-35% increase for induced C-domain transformants compared to controls. The data suggest that ectopic expression of the calreticulin C-domain increases Ca2+ stores, and that this Ca2+ reserve can be used by the plant in times of stress.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Agrobacterium tumefaciens / genetics
  • Arabidopsis / genetics*
  • Arabidopsis / growth & development
  • Biological Availability
  • Calcium / metabolism*
  • Calcium-Binding Proteins / chemistry
  • Calcium-Binding Proteins / metabolism*
  • Calreticulin
  • Genetic Vectors
  • Green Fluorescent Proteins
  • Luminescent Proteins / genetics
  • Phenotype
  • Plants, Genetically Modified
  • Ribonucleoproteins / chemistry
  • Ribonucleoproteins / metabolism*
  • Zea mays / genetics
  • Zea mays / metabolism*

Substances

  • Calcium-Binding Proteins
  • Calreticulin
  • Luminescent Proteins
  • Ribonucleoproteins
  • Green Fluorescent Proteins
  • Calcium