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Scooped by Ryohei Thomas Nakano
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Origin and function of stomata in the moss Physcomitrella patens

Origin and function of stomata in the moss Physcomitrella patens | Development | Scoop.it
Stomata are microscopic valves on plant surfaces that originated over 400 million years (Myr) ago and facilitated the greening of Earth's continents by permitting efficient shoot–atmosphere gas exchange and plant hydration1. However, the core genetic machinery regulating stomatal development in non-vascular land plants is poorly understood2,​3,​4 and their function has remained a matter of debate for a century5. Here, we show that genes encoding the two basic helix–loop–helix proteins PpSMF1 (SPEECH, MUTE and FAMA-like) and PpSCREAM1 (SCRM1) in the moss Physcomitrella patens are orthologous to transcriptional regulators of stomatal development in the flowering plant Arabidopsis thaliana and essential for stomata formation in moss. Targeted P. patens knockout mutants lacking either PpSMF1 or PpSCRM1 develop gametophytes indistinguishable from wild-type plants but mutant sporophytes lack stomata. Protein–protein interaction assays reveal heterodimerization between PpSMF1 and PpSCRM1, which, together with moss–angiosperm gene complementations6, suggests deep functional conservation of the heterodimeric SMF1 and SCRM1 unit is required to activate transcription for moss stomatal development, as in A. thaliana7. Moreover, stomata-less sporophytes of ΔPpSMF1 and ΔPpSCRM1 mutants exhibited delayed dehiscence, implying stomata might have promoted dehiscence in the first complex land-plant sporophytes.
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Plant development regulated by cytokinin sinks

Plant development regulated by cytokinin sinks | Development | Scoop.it
Morphogenetic signals control the patterning of multicellular organisms. Cytokinins are mobile signals that are perceived by subsets of plant cells. We found that the responses to cytokinin signaling during Arabidopsis development are constrained by the transporter PURINE PERMEASE 14 (PUP14). In our experiments, the expression of PUP14 was inversely correlated to the cytokinin signaling readout. Loss of PUP14 function allowed ectopic cytokinin signaling accompanied by aberrant morphogenesis in embryos, roots, and the shoot apical meristem. PUP14 protein localized to the plasma membrane and imported bioactive cytokinins, thus depleting apoplastic cytokinin pools and inhibiting perception by plasma membrane–localized cytokinin sensors to create a sink for active ligands. We propose that the spatiotemporal cytokinin sink patterns established by PUP14 determine the cytokinin signaling landscape that shapes the morphogenesis of land plants.
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Nature Genetics: Genome-wide association study using cellular traits identifies a new regulator of root development in Arabidopsis

Nature Genetics: Genome-wide association study using cellular traits identifies a new regulator of root development in Arabidopsis | Development | Scoop.it

With the increased availability of high-resolution sequence information, genome-wide association (GWA) studies have become feasible in a number of species1, 2, 3, 4, 5, 6, 7, 8. The vast majority of these studies are conducted in human populations, where it is difficult to provide strong evidence for the functional involvement of unknown genes that are identified using GWA. Here we used the model organism Arabidopsis thaliana to combine high-throughput confocal microscopy imaging of traits at the cellular level, GWA and expression analyses to identify genomic regions that are associated with developmental cell–type traits. We identify and characterize a new F-box gene, KUK, that regulates meristem and cell length. We further show that polymorphisms in the coding sequence are the major causes of KUKallele–dependent natural variation in root development. This work demonstrates the feasibility of GWA using cellular traits to identify causal genes for basic biological processes such as development.

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Cell: Retraction Notice to: A PLETHORA-Auxin Transcription Module Controls Cell Division Plane Rotation through MAP65 and CLASP

Refers To

Pankaj Dhonukshe, Daan A. Weits, Alfredo Cruz-Ramirez, Eva E. Deinum, Simon H. Tindemans, Klementina Kakar, Kalika Prasad, Ari Pekka Mähönen, Chris Ambrose, Michiko Sasabe, Guy Wachsmann, Marijn Luijten, Tom Bennett, Yasunori Machida, Renze Heidstra, Geoffrey Wasteneys, Bela M. Mulder, Ben Scheres

 

RETRACTED: A PLETHORA-Auxin Transcription Module Controls Cell Division Plane Rotation through MAP65 and CLASP

 

Cell, Volume 149, Issue 2, 13 April 2012, Pages 383-396

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TPC: Rho of Plant GTPase Signaling Regulates the Behavior of Arabidopsis Kinesin-13A to Establish Secondary Cell Wall Patterns

Plant cortical microtubule arrays determine the cell wall deposition pattern and proper cell shape and function. Although various microtubule-associated proteins regulate the cortical microtubule array, the mechanisms underlying marked rearrangement of cortical microtubules during xylem differentiation are not fully understood. Here, we show that local Rho of Plant (ROP) GTPase signaling targets an Arabidopsis thaliana kinesin-13 protein, Kinesin-13A, to cortical microtubules to establish distinct patterns of secondary cell wall formation in xylem cells. Kinesin-13A was preferentially localized with cortical microtubules in secondary cell wall pits, areas where cortical microtubules are depolymerized to prevent cell wall deposition. This localization of Kinesin-13A required the presence of the activated ROP GTPase, MICROTUBULE DEPLETION DOMAIN1 (MIDD1) protein, and cortical microtubules. Knockdown of Kinesin-13A resulted in the formation of smaller secondary wall pits, while overexpression of Kinesin-13A enlarged their surface area. Kinesin-13A alone could depolymerize microtubules in vitro; however, both MIDD1 and Kinesin-13A were required for the depolymerization of cortical microtubules in vivo. These results indicate that Kinesin-13A regulates the formation of secondary wall pits by promoting cortical microtubule depolymerization via the ROP-MIDD1 pathway.

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Quiescent center initiation in the Arabidopsis lateral root primordia is dependent on the SCARECROW transcription factor

Quiescent center initiation in the Arabidopsis lateral root primordia is dependent on the SCARECROW transcription factor | Development | Scoop.it
Lateral root formation is an important determinant of root system architecture. In Arabidopsis, lateral roots originate from pericycle cells, which undergo a program of morphogenesis to generate a new lateral root meristem. Despite its importance for root meristem organization, the onset of quiescent center (QC) formation during lateral root morphogenesis remains unclear. Here, we used live 3D confocal imaging to monitor cell organization and identity acquisition during lateral root development. Our dynamic observations revealed an early morphogenesis phase and a late meristem formation phase as proposed in the bi-phasic growth model. Establishment of lateral root QCs coincided with this developmental phase transition. QC precursor cells originated from the outer layer of stage II lateral root primordia, within which the SCARECROW (SCR) transcription factor was specifically expressed. Disrupting SCR function abolished periclinal divisions in this lateral root primordia cell layer and perturbed the formation of QC precursor cells. We conclude that de novo QC establishment in lateral root primordia operates via SCR-mediated formative cell division and coincides with the developmental phase transition.
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A Secreted Peptide and Its Receptors Shape the Auxin Response Pattern and Leaf Margin Morphogenesis

Highlights 
•EPFL2 peptide and ERECTA family receptors are required for leaf tooth growth 
•EPFL2 peptide and ERECTA family proteins constitute ligand-receptor pairs 
•The EPFL2-ERECTA family system represses auxin response in growing leaf margin 
•Auxin represses the EPFL2 expression, forming a negative feedback circuit 

Summary 
Secreted peptides mediate intercellular communication [ 1, 2 ]. Several secreted peptides in the EPIDERMAL PATTERNING FACTOR-LIKE (EPFL) family regulate morphogenesis of tissues, such as stomata and inflorescences in plants [ 3–15 ]. The biological functions of other EPFL family members remain unknown. Here, we show that the EPFL2 gene is required for growth of leaf teeth. EPFL2 peptide physically interacts with ERECTA (ER) family receptor-kinases and, accordingly, the attenuation of ER family activities leads to formation of toothless leaves. During the tooth growth process, responses to the phytohormone auxin are maintained at tips of the teeth to promote their growth [ 16–19 ]. In the growing tooth tip of epfl2 and multiple er family mutants, the auxin response becomes broader. Conversely, overexpression of EPFL2 diminishes the auxin response, indicating that the EPFL2 signal restricts the auxin response to the tooth tip. Interestingly, the tip-specific auxin response in turn organizes characteristic expression patterns of ER family and EPFL2 by enhancing ER family expression at the tip while eliminating the EPFL2 expression from the tip. Our findings identify the novel ligand-receptor pairs promoting the tooth growth, and further reveal a feedback circuit between the peptide-receptor system and auxin response as a mechanism for maintaining proper auxin maxima during leaf margin morphogenesis.

Via Pierre-Marc Delaux
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TPC: Plastid-Localized Glutathione Reductase2–Regulated Glutathione Redox Status Is Essential for Arabidopsis Root Apical Meristem Maintenance

Glutathione is involved in thiol redox signaling and acts as a major redox buffer against reactive oxygen species, helping to maintain a reducing environment in vivo. Glutathione reductase (GR) catalyzes the reduction of glutathione disulfide (GSSG) into reduced glutathione (GSH). The Arabidopsis thaliana genome encodes two GRs: GR1 and GR2. Whereas the cytosolic/peroxisomal GR1 is not crucial for plant development, we show here that the plastid-localized GR2 is essential for root growth and root apical meristem (RAM) maintenance. We identify a GR2 mutant, miao, that displays strong inhibition of root growth and severe defects in the RAM, with GR activity being reduced to ∼50%. miaoaccumulates high levels of GSSG and exhibits increased glutathione oxidation. The exogenous application of GSH or the thiol-reducing agent DTT can rescue the root phenotype of miao, demonstrating that the RAM defects in miao are triggered by glutathione oxidation. Our in silico analysis of public microarray data shows that auxin and glutathione redox signaling generally act independently at the transcriptional level. We propose that glutathione redox status is essential for RAM maintenance through both auxin/PLETHORA (PLT)-dependent and auxin/PLT-independent redox signaling pathways.

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