Abstract
Many plants improve their phosphate (Pi) availability by forming mutualistic associations with arbuscular mycorrhizal (AM) fungi. Pi-repleted plants are much less colonized by AM fungi than Pi-depleted plants. This indicates a link between plant Pi signaling and AM development. MicroRNAs (miR) of the 399 family are systemic Pi-starvation signals important for maintenance of Pi homeostasis in Arabidopsis thaliana and might also qualify as signals regulating AM development in response to Pi availability. MiR399 could either represent the systemic low-Pi signal promoting or required for AM formation or they could act as counter players of systemic Pi-availability signals that suppress AM symbiosis. To test either of these assumptions, we analyzed the miR399 family in the AM-capable plant model Medicago truncatula and could experimentally confirm 10 novel MIR399 genes in this species. Pi-depleted plants showed increased expression of mature miR399 and multiple pri-miR399, and unexpectedly, levels of five of the 15 pri-miR399 species were higher in leaves of mycorrhizal plants than in leaves of nonmycorrhizal plants. Compared with nonmycorrhizal Pi-depleted roots, mycorrhizal roots of Pi-depleted M. truncatula and tobacco plants had increased Pi contents due to symbiotic Pi uptake but displayed higher mature miR399 levels. Expression levels of MtPho2 remained low and PHO2-dependent Pi-stress marker transcript levels remained high in these mycorrhizal roots. Hence, an AM symbiosis-related signal appears to increase miR399 expression and decrease PHO2 activity. MiR399 overexpression in tobacco suggested that miR399 alone is not sufficient to improve mycorrhizal colonization supporting the assumption that, in mycorrhizal roots, increased miR399 are necessary to keep the MtPho2 expression and activity low, which would otherwise increase in response to symbiotic Pi uptake.
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Claims 11
Claim · model-written summary
Ten novel MIR399 genes were confirmed in Medicago truncatula.
- Taxon
- Medicago truncatula
Medicago truncatulae0 - Gene
- MIR399e0
- Outcome
- novel MIR399 genese0
- Value
- 10e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we analyzed the miR399 family in the AM-capable plant model Medicago truncatula and could experimentally confirm 10 novel MIR399 genes in this species.”
Claim · model-written summary
Pi depletion increased mature miR399 and multiple pri-miR399 expression.
- Taxon
- Medicago truncatulaMedicago truncatulae1
- Treatment
- Pi-depletede0
- Gene
- miR399e0
- Outcome
- expression of mature miR399 and multiple pri-miR399e0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Pi-depleted plants showed increased expression of mature miR399 and multiple pri-miR399”
e1“Medicago truncatula”
Claim · model-written summary
Five of 15 pri-miR399 species had higher leaf levels in mycorrhizal than nonmycorrhizal plants.
- Taxon
- Medicago truncatulaMedicago truncatulae1
- Organ / stage
- leavese0
- Gene
- pri-miR399e0
- Outcome
- levels of five of the 15 pri-miR399 speciese0
- Direction
- highere0
- Comparator
- nonmycorrhizal plantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“levels of five of the 15 pri-miR399 species were higher in leaves of mycorrhizal plants than in leaves of nonmycorrhizal plants.”
e1“Medicago truncatula”
Claim · model-written summary
Mycorrhizal Medicago roots had increased Pi contents compared with nonmycorrhizal Pi-depleted roots.
- Taxon
- M. truncatulaMedicago truncatulae0
- Organ / stage
- rootse0
- Outcome
- Pi contentse0
- Direction
- increasede0
- Comparator
- nonmycorrhizal Pi-depleted rootse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Compared with nonmycorrhizal Pi-depleted roots, mycorrhizal roots of Pi-depleted M. truncatula and tobacco plants had increased Pi contents due to symbiotic Pi uptake”
Claim · model-written summary
Mycorrhizal tobacco roots had increased Pi contents compared with nonmycorrhizal Pi-depleted roots.
- Taxon
- tobacco
Nicotiana tabacume0 - Organ / stage
- rootse0
- Outcome
- Pi contentse0
- Direction
- increasede0
- Comparator
- nonmycorrhizal Pi-depleted rootse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Compared with nonmycorrhizal Pi-depleted roots, mycorrhizal roots of Pi-depleted M. truncatula and tobacco plants had increased Pi contents due to symbiotic Pi uptake”
Claim · model-written summary
Mycorrhizal Medicago roots displayed higher mature miR399.
- Taxon
- M. truncatulaMedicago truncatulae0
- Organ / stage
- rootse0
- Gene
- miR399e0
- Outcome
- mature miR399 levelse0
- Direction
- highere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“mycorrhizal roots of Pi-depleted M. truncatula and tobacco plants had increased Pi contents due to symbiotic Pi uptake but displayed higher mature miR399 levels.”
Claim · model-written summary
Mycorrhizal tobacco roots displayed higher mature miR399.
- Taxon
- tobaccoNicotiana tabacume0
- Organ / stage
- rootse0
- Gene
- miR399e0
- Outcome
- mature miR399 levelse0
- Direction
- highere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“mycorrhizal roots of Pi-depleted M. truncatula and tobacco plants had increased Pi contents due to symbiotic Pi uptake but displayed higher mature miR399 levels.”
Claim · model-written summary
MtPho2 expression remained low in mycorrhizal roots.
- Taxon
- Medicago truncatulaMedicago truncatulae1
- Gene
- MtPho2e0
- Outcome
- Expression levels of MtPho2e0
- Direction
- remained lowe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Expression levels of MtPho2 remained low and PHO2-dependent Pi-stress marker transcript levels remained high in these mycorrhizal roots.”
e1“Medicago truncatula”
Claim · model-written summary
PHO2-dependent Pi-stress transcripts remained high in mycorrhizal roots.
- Taxon
- Medicago truncatulaMedicago truncatulae1
- Gene
- PHO2e0
- Outcome
- Pi-stress marker transcript levelse0
- Direction
- remained highe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“PHO2-dependent Pi-stress marker transcript levels remained high in these mycorrhizal roots.”
e1“Medicago truncatula”
Claim · model-written summary
The authors infer a mycorrhizal signal increases miR399 expression and decreases PHO2 activity.
- Taxon
- Medicago truncatulaMedicago truncatulae1
- Gene
- miR399e0
- Outcome
- miR399 expression and decrease PHO2 activitye0
- Qualifier
- AM symbiosis-related signale0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“an AM symbiosis-related signal appears to increase miR399 expression and decrease PHO2 activity.”
e1“Medicago truncatula”
Claim · model-written summary
Tobacco miR399 overexpression alone was insufficient to improve mycorrhizal colonization.
- Taxon
- tobaccoNicotiana tabacume0
- Treatment
- MiR399 overexpressione0
- Outcome
- mycorrhizal colonizatione0
- Direction
- not sufficient to improvee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“MiR399 overexpression in tobacco suggested that miR399 alone is not sufficient to improve mycorrhizal colonization”