The class VIII myosin ATM1 is required for root apical meristem function
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Abstract
Myosins are evolutionarily conserved motor proteins that interact with actin filaments to regulate organelle transport, cytoplasmic streaming and cell growth. Plant-specific class XI myosin proteins direct cell division and root organogenesis. However, the roles of plant-specific class VIII myosin proteins in plant growth and development are less understood. Here, we investigated the function of an auxin-regulated class VIII myosin, Arabidopsis thaliana MYOSIN 1 (ATM1), using genetics, transcriptomics and live cell microscopy. ATM1 is associated with the plasma membrane and plasmodesmata within the root apical meristem (RAM). Loss of ATM1 function results in decreased RAM size and reduced cell proliferation in a sugar-dependent manner. Auxin signaling and transcriptional responses were dampened in atm1-1 roots. Complementation of atm1-1 with a tagged ATM1 driven under the native ATM1 promoter restored root growth and cell cycle progression. Genetic analyses of atm1-1 seedlings with HEXOKINASE 1 (HXK1) and TARGET OF RAPAMYCIN COMPLEX 1 (TORC1) overexpression lines indicate that ATM1 is downstream of TOR. Collectively, these results provide previously unreported evidence that ATM1 functions to influence cell proliferation in primary roots in response to auxin and sugar cues.
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Transcriptomic analysis of atm1-1 seedlings in response to sugars
Was there altered expression of other myosins? or cytoskeletal proteins?
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(Fig. S1)
Is there a reason the +Suc propidium iodide staining is so much brighter than +Mock WT? is Propidium iodide staining just pretty inconsistent in these cells?
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florescence
Just a minor point. I think y'all meant fluorescence.
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ATM1 promoter is expressed during post-embryogenic root organogenesis in Arabidopsis thaliana.
What is marked in red? is that propidium iodide like in Fig 2D?
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Compared to WT, under sugar-free conditions, the layer of columella stem cell daughter cells (CSCDs) was absent in atm1-1 (Fig. 4E), suggesting that the competence of these cells to properly differentiate is altered. Under sugar supplementation conditions, the size of the CSCDs and the fully differentiated columella cells (DCCs) were reduced in atm1-1 compared to WT plants but not the number of cells (Fig. 4E).
Wow! This is a very striking and exciting finding! Was the cell/layer count consistent across 100% of roots? It'd be great to see quantification of that as well. the Recovered number when sucrose is added is super cool!
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nt center: ***
The first image in Panel E has 2 asterisks instead of the 3. Not sure if intentional.
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(A) Phenotypes of 5-day-old atm1-1 plants with reduced root length compared to wild type on 0.5 X Murashige and Skoog (MS) medium without or with 15 mM Sucrose (Suc) at 45 μmol m-1 s-1 LD conditions. (B) Quantitative analysis of root growth in Col-0 and atm1-1 seedlings. n=10; ***P<0.001, two-way ANOVA and Tukey’s multiple comparison test. (
Is this just redundant w/ Fig 2 BC? I see that the values are a lot higher in Fig 2 BC and those were 6-day old, instead of the 5-day old plants shown here. Sorry if it's an ignorant question.
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(Fig. S1)
Is there a reason the +Suc propidium iodide staining is so much brighter than +Mock WT? is Propidium iodide staining just pretty inconsistent in these cells?
-
Transcriptomic analysis of atm1-1 seedlings in response to sugars
Was there altered expression of other myosins? or cytoskeletal proteins?
-
Compared to WT, under sugar-free conditions, the layer of columella stem cell daughter cells (CSCDs) was absent in atm1-1 (Fig. 4E), suggesting that the competence of these cells to properly differentiate is altered. Under sugar supplementation conditions, the size of the CSCDs and the fully differentiated columella cells (DCCs) were reduced in atm1-1 compared to WT plants but not the number of cells (Fig. 4E).
Wow! This is a very striking and exciting finding! Was the cell/layer count consistent across 100% of roots? It'd be great to see quantification of that as well. the Recovered number when sucrose is added is super cool!
-
florescence
Just a minor point. I think y'all meant fluorescence.
-
nt center: ***
The first image in Panel E has 2 asterisks instead of the 3. Not sure if intentional.
-
(A) Phenotypes of 5-day-old atm1-1 plants with reduced root length compared to wild type on 0.5 X Murashige and Skoog (MS) medium without or with 15 mM Sucrose (Suc) at 45 μmol m-1 s-1 LD conditions. (B) Quantitative analysis of root growth in Col-0 and atm1-1 seedlings. n=10; ***P<0.001, two-way ANOVA and Tukey’s multiple comparison test. (
Is this just redundant w/ Fig 2 BC? I see that the values are a lot higher in Fig 2 BC and those were 6-day old, instead of the 5-day old plants shown here. Sorry if it's an ignorant question.
-
ATM1 promoter is expressed during post-embryogenic root organogenesis in Arabidopsis thaliana.
What is marked in red? is that propidium iodide like in Fig 2D?
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