Abstract
Internal compartmentalization of metals is an important metal tolerance mechanism in many organisms. In plants and fungi, sequestration into the vacuole is a major detoxification mechanism for metals. Cation transport into the vacuole can be mediated by CAX (cation exchanger) transporters. The Arabidopsis thaliana AtCAX2 transporter was shown previously to transport Ca(2+), Cd(2+) and Mn(2+). To assess the conservation of the functional and regulatory characteristics of CAX2-like transporters in higher plants, we have characterized AtCAX2 orthologues from Arabidopsis (AtCAX5), tomato (LeCAX2) and barley (HvCAX2). Substrate specificity and regulatory activity were assessed using a yeast heterologous-expression assay. Each CAX could transport Ca(2+) and Mn(2+) into the yeast vacuole, but they each had different cation transport kinetics. Most notably, there was variation in the regulation of the transporters. As found with AtCAX2 previously, only expression of an N-terminally truncated form of AtCAX5 in yeast was able to mediate Ca(2+) and Mn(2+) transport, indicating that activity may be controlled by an autoregulatory region at the N-terminus. In contrast, either full-length or truncated LeCAX2 could efficiently transport Ca(2+), although Mn(2+) transport was controlled by the N-terminus. HvCAX2 did not appear to possess an N-terminal regulatory domain. Expression of AtCAX2 was not significantly modulated by metal stress; however, AtCAX5 and HvCAX2 were transcriptionally up-regulated by high Mn(2+) treatment, and by Ca(2+) and Na(+) stress respectively. It is therefore apparent that, despite the high sequence identity between plant CAX2 orthologues, there is significant diversity in their functional characteristics, particularly with regard to regulatory mechanisms.
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Claims 11
Claim · model-written summary
Only an N-terminally truncated form of AtCAX5 expressed in yeast mediated Ca(2+) and Mn(2+) transport.
- Taxon
- Arabidopsis
Arabidopsise2 - Gene
- AtCAX5e1
- Outcome
- Ca(2+) and Mn(2+) transporte1
- Setting
- yeaste1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“only expression of an N-terminally truncated form of AtCAX5 in yeast was able to mediate Ca(2+) and Mn(2+) transport”
e2“orthologues from Arabidopsis (AtCAX5), tomato (LeCAX2) and barley (HvCAX2)”
Claim · model-written summary
Full-length or truncated LeCAX2 could efficiently transport Ca(2+).
- Taxon
- tomato
Solanum lycopersicume2 - Gene
- LeCAX2e3
- Outcome
- transport Ca(2+)e3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e3“In contrast, either full-length or truncated LeCAX2 could efficiently transport Ca(2+), although Mn(2+) transport was controlled by the N-terminus”
e2“orthologues from Arabidopsis (AtCAX5), tomato (LeCAX2) and barley (HvCAX2)”
Claim · model-written summary
Mn(2+) transport by LeCAX2 was controlled by its N-terminus.
- Taxon
- tomatoSolanum lycopersicume2
- Gene
- LeCAX2e3
- Outcome
- Mn(2+) transporte3
- Qualifier
- was controlled by the N-terminuse3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e3“In contrast, either full-length or truncated LeCAX2 could efficiently transport Ca(2+), although Mn(2+) transport was controlled by the N-terminus”
e2“orthologues from Arabidopsis (AtCAX5), tomato (LeCAX2) and barley (HvCAX2)”
Claim · model-written summary
HvCAX2 did not appear to possess an N-terminal regulatory domain.
- Taxon
- barley
.jpg?width=60)
Hordeum vulgaree2 - Gene
- HvCAX2e4
- Outcome
- N-terminal regulatory domaine4
- Qualifier
- did not appear to possesse4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
.jpg?width=500)
Verbatim
e4“HvCAX2 did not appear to possess an N-terminal regulatory domain”
e2“orthologues from Arabidopsis (AtCAX5), tomato (LeCAX2) and barley (HvCAX2)”
Claim · model-written summary
HvCAX2 transported Ca(2+) and Mn(2+) into the yeast vacuole.
- Taxon
- barleyHordeum vulgaree2
- Gene
- HvCAX2e2
- Outcome
- transport Ca(2+) and Mn(2+)e5
- Setting
- yeaste5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e5“Each CAX could transport Ca(2+) and Mn(2+) into the yeast vacuole, but they each had different cation transport kinetics”
e2“orthologues from Arabidopsis (AtCAX5), tomato (LeCAX2) and barley (HvCAX2)”
Claim · model-written summary
AtCAX5 was transcriptionally up-regulated by high Mn(2+) treatment.
- Taxon
- ArabidopsisArabidopsise2
- Treatment
- high Mn(2+) treatmente6
- Gene
- AtCAX5e6
- Outcome
- transcriptionally up-regulatede6
- Direction
- up-regulatede6
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e6“AtCAX5 and HvCAX2 were transcriptionally up-regulated by high Mn(2+) treatment, and by Ca(2+) and Na(+) stress respectively”
e2“orthologues from Arabidopsis (AtCAX5), tomato (LeCAX2) and barley (HvCAX2)”
Claim · model-written summary
HvCAX2 was transcriptionally up-regulated by high Mn(2+) treatment.
- Taxon
- barleyHordeum vulgaree2
- Treatment
- high Mn(2+) treatmente6
- Gene
- HvCAX2e6
- Outcome
- transcriptionally up-regulatede6
- Direction
- up-regulatede6
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e6“AtCAX5 and HvCAX2 were transcriptionally up-regulated by high Mn(2+) treatment, and by Ca(2+) and Na(+) stress respectively”
e2“orthologues from Arabidopsis (AtCAX5), tomato (LeCAX2) and barley (HvCAX2)”
Claim · model-written summary
AtCAX5 was transcriptionally up-regulated by Ca(2+) stress.
- Taxon
- ArabidopsisArabidopsise2
- Treatment
- Ca(2+) and Na(+) stresse6
- Gene
- AtCAX5e6
- Outcome
- transcriptionally up-regulatede6
- Direction
- up-regulatede6
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Schema note from the model: "respectively" pairing read in listed order (AtCAX5 with Ca(2+), HvCAX2 with Na(+)); treatment field keeps both stresses
Verbatim
e6“AtCAX5 and HvCAX2 were transcriptionally up-regulated by high Mn(2+) treatment, and by Ca(2+) and Na(+) stress respectively”
e2“orthologues from Arabidopsis (AtCAX5), tomato (LeCAX2) and barley (HvCAX2)”
Claim · model-written summary
HvCAX2 was transcriptionally up-regulated by Na(+) stress.
- Taxon
- barleyHordeum vulgaree2
- Treatment
- Ca(2+) and Na(+) stresse6
- Gene
- HvCAX2e6
- Outcome
- transcriptionally up-regulatede6
- Direction
- up-regulatede6
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Schema note from the model: "respectively" pairing read in listed order (AtCAX5 with Ca(2+), HvCAX2 with Na(+)); treatment field keeps both stresses
Verbatim
e6“AtCAX5 and HvCAX2 were transcriptionally up-regulated by high Mn(2+) treatment, and by Ca(2+) and Na(+) stress respectively”
e2“orthologues from Arabidopsis (AtCAX5), tomato (LeCAX2) and barley (HvCAX2)”
Claim · model-written summary
Expression of AtCAX2 was not significantly modulated by metal stress.
- Taxon
- ArabidopsisArabidopsise2
- Treatment
- metal stresse7
- Gene
- AtCAX2e7
- Outcome
- Expressione7
- Direction
- not significantly modulatede7
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e7“Expression of AtCAX2 was not significantly modulated by metal stress”
e2“orthologues from Arabidopsis (AtCAX5), tomato (LeCAX2) and barley (HvCAX2)”
Claim · model-written summary
AtCAX5, LeCAX2 and HvCAX2 differed in cation transport kinetics.
- Taxon
- ArabidopsisArabidopsise2
- Outcome
- cation transport kineticse5
- Qualifier
- they each had differente5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Schema note from the model: comparison across orthologues from three plants; taxon is the first plant named
Verbatim
e5“Each CAX could transport Ca(2+) and Mn(2+) into the yeast vacuole, but they each had different cation transport kinetics”
e2“orthologues from Arabidopsis (AtCAX5), tomato (LeCAX2) and barley (HvCAX2)”
The same questions in other papers
heavy metal · molecular: expression · ArabidopsisPositive and negative results
2 papers in the same direction as this paper · 5 in the opposite direction
- positive
- positive
- positive
4 papers more in this group
See all 8 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.