Abstract
In the primary root and young hypocotyl of Arabidopsis, ACAULIS5 promotes translation of SUPPRESSOR OF ACAULIS51 (SAC51) and thereby inhibits cytokinin biosynthesis and vascular cell division. In this study, the relationships between ACAULIS5, SAC51 and cytokinin biosynthesis were investigated during secondary growth of Populus stems. Overexpression of ACAULIS5 from the constitutive 35S promoter in hybrid aspen (Populus tremula × Populus tremuloides) trees suppressed the expression level of ACAULIS5, which resulted in low levels of the physiologically active cytokinin bases as well as their direct riboside precursors in the transgenic lines. Low ACAULIS5 expression and low cytokinin levels of the transgenic trees coincided with low cambial activity of the stem. ACAULIS5 therefore, contrary to its function in young seedlings in Arabidopsis, stimulates cytokinin accumulation and cambial activity during secondary growth of the stem. This function is not derived from maturing secondary xylem tissues as transgenic suppression of ACAULIS5 levels in these tissues did not influence secondary growth. Interestingly, evidence was obtained for increased activity of the anticlinal division of the cambial initials under conditions of low ACAULIS5 expression and low cytokinin accumulation. We propose that ACAULIS5 integrates auxin and cytokinin signalling to promote extensive secondary growth of tree stems.
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Claims 7
Claim · model-written summary
Constitutive ACAULIS5 overexpression suppressed ACAULIS5 expression in hybrid aspen.
- Taxon
- hybrid aspene0
- Treatment
- Overexpression of ACAULIS5 from the constitutive 35S promotere0
- Gene
- ACAULIS5e0
- Outcome
- expression level of ACAULIS5e0
- Direction
- suppressede0
Not reportedComparator
Verbatim
e0“Overexpression of ACAULIS5 from the constitutive 35S promoter in hybrid aspen (Populus tremula × Populus tremuloides) trees suppressed the expression level of ACAULIS5”
Claim · model-written summary
The ACAULIS5 transgenic lines had low physiologically active cytokinin base levels.
PopulusOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“low levels of the physiologically active cytokinin bases as well as their direct riboside precursors in the transgenic lines”
t0“Populus Trees”
Claim · model-written summary
The ACAULIS5 transgenic lines had low cytokinin riboside precursor levels.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“low levels of the physiologically active cytokinin bases as well as their direct riboside precursors in the transgenic lines”
t0“Populus Trees”
Claim · model-written summary
Low ACAULIS5 expression and cytokinin levels coincided with low stem cambial activity.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Low ACAULIS5 expression and low cytokinin levels of the transgenic trees coincided with low cambial activity of the stem.”
t0“Populus Trees”
Claim · model-written summary
Suppressing ACAULIS5 in maturing secondary xylem did not influence secondary growth.
- Organ / stage
- maturing secondary xylem tissuese1
- Treatment
- transgenic suppression of ACAULIS5 levelse0
- Gene
- ACAULIS5e0
- Outcome
- secondary growthe0
- Direction
- did not influencee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“transgenic suppression of ACAULIS5 levels in these tissues did not influence secondary growth.”
e1“maturing secondary xylem tissues”
t0“Populus Trees”
Claim · model-written summary
Low ACAULIS5 expression and cytokinin accumulation were associated with increased anticlinal division of cambial initials.
- Gene
- ACAULIS5e0
- Outcome
- activity of the anticlinal division of the cambial initialse0
- Direction
- increasede0
- Qualifier
- low ACAULIS5 expression and low cytokinin accumulatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“increased activity of the anticlinal division of the cambial initials under conditions of low ACAULIS5 expression and low cytokinin accumulation.”
t0“Populus Trees”
Claim · model-written summary
The authors propose that ACAULIS5 integrates auxin and cytokinin signalling to promote secondary stem growth.
- Gene
- ACAULIS5e0
- Outcome
- extensive secondary growth of tree stemse0
- Qualifier
- integrates auxin and cytokinin signallinge0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We propose that ACAULIS5 integrates auxin and cytokinin signalling to promote extensive secondary growth of tree stems.”
t0“Populus Trees”
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