Abstract
The physiological role and mechanism of nutrient storage within vacuoles of specific cell types is poorly understood. Transcript profiles from Arabidopsis thaliana leaf cells differing in calcium concentration ([Ca], epidermis <10 mM versus mesophyll >60 mM) were compared using a microarray screen and single-cell quantitative PCR. Three tonoplast-localized Ca(2+) transporters, CAX1 (Ca(2+)/H(+)-antiporter), ACA4, and ACA11 (Ca(2+)-ATPases), were identified as preferentially expressed in Ca-rich mesophyll. Analysis of respective loss-of-function mutants demonstrated that only a mutant that lacked expression of both CAX1 and CAX3, a gene ectopically expressed in leaves upon knockout of CAX1, had reduced mesophyll [Ca]. Reduced capacity for mesophyll Ca accumulation resulted in reduced cell wall extensibility, stomatal aperture, transpiration, CO(2) assimilation, and leaf growth rate; increased transcript abundance of other Ca(2+) transporter genes; altered expression of cell wall-modifying proteins, including members of the pectinmethylesterase, expansin, cellulose synthase, and polygalacturonase families; and higher pectin concentrations and thicker cell walls. We demonstrate that these phenotypes result from altered apoplastic free [Ca(2+)], which is threefold greater in cax1/cax3 than in wild-type plants. We establish CAX1 as a key regulator of apoplastic [Ca(2+)] through compartmentation into mesophyll vacuoles, a mechanism essential for optimal plant function and productivity.
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Claims 15
Claim · model-written summary
Leaf epidermis had less than 10 mM calcium and mesophyll more than 60 mM.
- Taxon
- Arabidopsis thaliana
Arabidopsis thalianae0 - Organ / stage
- leaf cellse0
- Outcome
- calcium concentratione0
- Value
- epidermis <10 mM versus mesophyll >60 mMe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis thaliana leaf cells differing in calcium concentration ([Ca], epidermis <10 mM versus mesophyll >60 mM)”
Claim · model-written summary
CAX1, ACA4 and ACA11 were preferentially expressed in calcium-rich mesophyll.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- mesophylle0
- Gene
- CAX1e0
- Outcome
- preferentially expressede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“CAX1 (Ca(2+)/H(+)-antiporter), ACA4, and ACA11 (Ca(2+)-ATPases), were identified as preferentially expressed in Ca-rich mesophyll”
t0“Arabidopsis”
t1“Arabidopsis”
Claim · model-written summary
Only the double loss of CAX1 and CAX3 reduced mesophyll calcium.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- lacked expression of both CAX1 and CAX3e0
- Gene
- CAX1 and CAX3e0
- Outcome
- mesophyll [Ca]e0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“only a mutant that lacked expression of both CAX1 and CAX3, a gene ectopically expressed in leaves upon knockout of CAX1, had reduced mesophyll [Ca]”
t0“Arabidopsis”
t1“Arabidopsis”
Claim · model-written summary
CAX3 was ectopically expressed in leaves after CAX1 knockout.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- leavese0
- Treatment
- knockout of CAX1e0
- Gene
- CAX3e0
- Outcome
- CAX3, a gene ectopically expressede0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“CAX3, a gene ectopically expressed in leaves upon knockout of CAX1”
t0“Arabidopsis”
t1“Arabidopsis”
Claim · model-written summary
Reduced mesophyll calcium accumulation reduced cell-wall extensibility.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- mesophylle0
- Compound
- Cae0
- Outcome
- cell wall extensibilitye0
- Direction
- reducede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Reduced capacity for mesophyll Ca accumulation resulted in reduced cell wall extensibility”
t0“Arabidopsis”
t1“Arabidopsis”
Claim · model-written summary
Reduced mesophyll calcium accumulation reduced stomatal aperture.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- mesophylle0
- Compound
- Cae0
- Outcome
- stomatal aperturee0
- Direction
- reducede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Reduced capacity for mesophyll Ca accumulation resulted in reduced cell wall extensibility, stomatal aperture”
t0“Arabidopsis”
t1“Arabidopsis”
Claim · model-written summary
Reduced mesophyll calcium accumulation reduced transpiration.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- mesophylle0
- Compound
- Cae0
- Outcome
- transpiratione0
- Direction
- reducede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Reduced capacity for mesophyll Ca accumulation resulted in reduced cell wall extensibility, stomatal aperture, transpiration”
t0“Arabidopsis”
t1“Arabidopsis”
Claim · model-written summary
Reduced mesophyll calcium accumulation reduced CO2 assimilation.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- mesophylle0
- Compound
- Cae0
- Outcome
- CO(2) assimilatione0
- Direction
- reducede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Reduced capacity for mesophyll Ca accumulation resulted in reduced cell wall extensibility, stomatal aperture, transpiration, CO(2) assimilation”
t0“Arabidopsis”
t1“Arabidopsis”
Claim · model-written summary
Reduced mesophyll calcium accumulation reduced leaf growth rate.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- mesophylle0
- Compound
- Cae0
- Outcome
- leaf growth ratee0
- Direction
- reducede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Reduced capacity for mesophyll Ca accumulation resulted in reduced cell wall extensibility, stomatal aperture, transpiration, CO(2) assimilation, and leaf growth rate”
t0“Arabidopsis”
t1“Arabidopsis”
Claim · model-written summary
Reduced mesophyll calcium accumulation increased transcript abundance of other calcium transporter genes.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- mesophylle1
- Outcome
- transcript abundance of other Ca(2+) transporter genese0
- Direction
- increasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“increased transcript abundance of other Ca(2+) transporter genes”
t0“Arabidopsis”
t1“Arabidopsis”
e1“Arabidopsis thaliana leaf cells differing in calcium concentration ([Ca], epidermis <10 mM versus mesophyll >60 mM)”
Claim · model-written summary
Reduced mesophyll calcium accumulation altered expression of cell-wall-modifying proteins.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- pectinmethylesterase, expansin, cellulose synthase, and polygalacturonase familiese0
- Outcome
- expression of cell wall-modifying proteinse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“altered expression of cell wall-modifying proteins, including members of the pectinmethylesterase, expansin, cellulose synthase, and polygalacturonase families”
t0“Arabidopsis”
t1“Arabidopsis”
Claim · model-written summary
Reduced mesophyll calcium accumulation increased pectin concentration.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- mesophylle1
- Outcome
- pectin concentrationse0
- Direction
- highere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“higher pectin concentrations and thicker cell walls”
t0“Arabidopsis”
t1“Arabidopsis”
e1“Arabidopsis thaliana leaf cells differing in calcium concentration ([Ca], epidermis <10 mM versus mesophyll >60 mM)”
Claim · model-written summary
Reduced mesophyll calcium accumulation increased cell-wall thickness.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- mesophylle1
- Outcome
- cell wallse0
- Direction
- thickere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“higher pectin concentrations and thicker cell walls”
t0“Arabidopsis”
t1“Arabidopsis”
e1“Arabidopsis thaliana leaf cells differing in calcium concentration ([Ca], epidermis <10 mM versus mesophyll >60 mM)”
Claim · model-written summary
Apoplastic free calcium was threefold greater in cax1/cax3 than wild type.
- Taxon
- ArabidopsisArabidopsist0
- Material
- cax1/cax3e0
- Outcome
- apoplastic free [Ca(2+)]e0
- Direction
- greatere0
- Value
- threefolde0
- Comparator
- wild-type plantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“apoplastic free [Ca(2+)], which is threefold greater in cax1/cax3 than in wild-type plants”
t0“Arabidopsis”
t1“Arabidopsis”
Claim · model-written summary
Altered apoplastic free calcium explains the mutant phenotypes.
- Taxon
- ArabidopsisArabidopsist0
- Compound
- [Ca(2+)]e0
- Outcome
- these phenotypese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“these phenotypes result from altered apoplastic free [Ca(2+)]”
t0“Arabidopsis”
t1“Arabidopsis”
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