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1. Distinct mechanisms orchestrate the contra-polarity of IRK and KOIN, two LRR-receptor-kinases controlling root cell division

   https://doi.org/10.1038/s41467-021-27913-1  

   Rodriguez-Furlan, Cecilia; Campos, Roya; Toth, Jessica N.; Van Norman, Jaimie M. (January 2022, Nature Communications)

   Abstract In plants, cell polarity plays key roles in coordinating developmental processes. Despite the characterization of several polarly localized plasma membrane proteins, the mechanisms connecting protein dynamics with cellular functions often remain unclear. Here, we introduce a polarized receptor, KOIN, that restricts cell divisions in the Arabidopsis root meristem. In the endodermis, KOIN polarity is opposite to IRK, a receptor that represses endodermal cell divisions. Their contra-polar localization facilitates dissection of polarity mechanisms and the links between polarity and function. We find that IRK and KOIN are recognized, sorted, and secreted through distinct pathways. IRK extracellular domains determine its polarity and partially rescue the mutant phenotype, whereas KOIN’s extracellular domains are insufficient for polar sorting and function. Endodermal expression of an IRK/KOIN chimera generates non-cell-autonomous misregulation of root cell divisions that impacts patterning. Altogether, we reveal two contrasting mechanisms determining these receptors’ polarity and link their polarity to cell divisions in root tissue patterning. 

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2. Outward askew endodermal cell divisions reveal INFLORESCENCE AND ROOT APICES RECEPTOR KINASE functions in division orientation

   https://doi.org/10.1093/plphys/kiae419  

   Rony, R_M_Imtiaz Karim; Campos, Roya; Pérez-Henríquez, Patricio; Van_Norman, Jaimie M (August 2024, Plant Physiology)

   Abstract Oriented cell divisions establish plant tissue and organ patterning and produce different cell types; this is particularly true of the highly organized Arabidopsis (Arabidopsis thaliana) root meristem. Mutant alleles of INFLORESCENCE AND ROOT APICES RECEPTOR KINASE (IRK) exhibit excess cell divisions in the root endodermis. IRK is a transmembrane receptor kinase that localizes to the outer polar domain of these cells, suggesting that directional signal perception is necessary to repress endodermal cell division. Here, a detailed examination revealed many of the excess endodermal divisions in irk have division planes that specifically skew toward the outer lateral side. Therefore, we termed them “outward askew” divisions. Expression of an IRK truncation lacking the kinase domain retains polar localization and prevents outward askew divisions in irk; however, the roots exhibit excess periclinal endodermal divisions. Using cell identity markers, we show that the daughters of outward askew divisions transition from endodermal to cortical identity similar to those of periclinal divisions. These results extend the requirement for IRK beyond repression of cell division activity to include cell division plane positioning. Based on its polarity, we propose that IRK at the outer lateral endodermal cell face participates in division plane positioning to ensure normal root ground tissue patterning. 

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3. Polarly localized receptor-like kinases PXC2 and IRK act redundantly during Arabidopsis root development in the radial axis

   https://doi.org/10.1101/2021.02.11.429611  

   Goff, Jason B (January 2021, bioRxiv)

   In plants, coordination of cell division and differentiation is critical for tissue patterning and organ development. Directional cell signaling and cell polarity have been proposed to participate in coordination of these developmental processes. For instance, a leucine-rich repeat receptor-like kinase (LRR-RLK) named INFLORESCENCE AND ROOT APICES KINASE (IRK) functions to restrict stele area and inhibit longitudinal anticlinal divisions (LADs) in the endodermis where it is polarly localized. The LRR-RLK most closely related to IRK is PXY/TDR CORRELATED 2 (PXC2) and we find that PXC2 shows similar polarized accumulation as IRK in root cell types. To further understand how these proteins operate in directional cell-cell signaling and root development we explored PXC2 function. pxc2 roots have an increase in stele area, indicating that PXC2 also functions to restrict stele size. Additionally, compared to either single mutant, irk pxc2 roots have an enhanced phenotype with further increases in endodermal LADs and stele area indicating redundant activities of these receptors. The double mutant also exhibits abnormal root growth, suggesting broader functions of PXC2 and IRK in the root. However, PXC2 is not functionally equivalent to IRK, as endodermal misexpression of PXC2 did not fully rescue irk. We propose that PXC2 is at least partially redundant to IRK with a more predominant role for IRK in repression of endodermal LADs. Our results are consistent with the hypothesis that repression of specific endodermal cell divisions and stele area through a PXC2/IRK-mediated directional signaling pathway is required for coordinated root growth and development. 

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4. Mutation of BAM2 rescues the sunn hypernodulation phenotype in Medicago truncatula, suggesting that a signaling pathway like CLV1/BAM in Arabidopsis affects nodule number

   https://doi.org/10.3389/fpls.2023.1334190  

   Thomas, Jacklyn; Frugoli, Julia (January 2024, Frontiers in Plant Science)

   The unique evolutionary adaptation of legumes for nitrogen-fixing symbiosis leading to nodulation is tightly regulated by the host plant. The autoregulation of nodulation (AON) pathway negatively regulates the number of nodules formed in response to the carbon/nitrogen metabolic status of the shoot and root by long-distance signaling to and from the shoot and root. Central to AON signaling in the shoots ofMedicago truncatulais SUNN, a leucine-rich repeat receptor-like kinase with high sequence similarity with CLAVATA1 (CLV1), part of a class of receptors inArabidopsisinvolved in regulating stem cell populations in the root and shoot. This class of receptors inArabidopsisincludes the BARELY ANY MERISTEM family, which, like CLV1, binds to CLE peptides and interacts with CLV1 to regulate meristem development.M. truncatulacontains five members of theBAMfamily, but onlyMtBAM1andMtBAM2are highly expressed in the nodules 48 hours after inoculation. Plants carry mutations in individualMtBAMs, and several doubleBAMmutant combinations all displayed wild-type nodule number phenotypes. However,Mtbam2suppressed thesunn-5hypernodulation phenotype and partially rescued the short root length phenotype ofsunn-5 when present in asunn-5background. Grafting determined thatbam2suppresses supernodulation from the roots, regardless of theSUNNstatus of the root. Overexpression ofMtBAM2in wild-type plants increases nodule numbers, while overexpression ofMtBAM2in somesunnmutants rescues the hypernodulation phenotype, but not the hypernodulation phenotypes of AON mutantrdn1-2orcrn. Relative expression measurements of the nodule transcription factor MtWOX5 downstream of the putativebam2 sunn-5complex revealed disruption of meristem signaling; while bothbam2andbam2 sunn-5influenceMtWOX5expression, the expression changes are in different directions. We propose a genetic model wherein the specific root interactions of BAM2/SUNN are critical for signaling in nodule meristem cell homeostasis inM. truncatula. 

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5. Comparative transcriptome analyses of the Drosophila pupal eye

   https://doi.org/10.1093/g3journal/jkaa003  

   DeAngelis, Miles W; Coolon, Joseph D; Johnson, Ruth I (January 2021, G3 Genes|Genomes|Genetics)

   Lott, S (Ed.)

   Abstract Tissue function is dependent on correct cellular organization and behavior. As a result, the identification and study of genes that contribute to tissue morphogenesis is of paramount importance to the fields of cell and developmental biology. Many of the genes required for tissue patterning and organization are highly conserved between phyla. This has led to the emergence of several model organisms and developmental systems that are used to study tissue morphogenesis. One such model is the Drosophila melanogaster pupal eye that has a highly stereotyped arrangement of cells. In addition, the pupal eye is postmitotic that allows for the study of tissue morphogenesis independent from any effects of proliferation. While the changes in cell morphology and organization that occur throughout pupal eye development are well documented, less is known about the corresponding transcriptional changes that choreograph these processes. To identify these transcriptional changes, we dissected wild-type Canton S pupal eyes and performed RNA-sequencing. Our analyses identified differential expression of many loci that are documented regulators of pupal eye morphogenesis and contribute to multiple biological processes including signaling, axon projection, adhesion, and cell survival. We also identified differential expression of genes not previously implicated in pupal eye morphogenesis such as components of the Toll pathway, several non-classical cadherins, and components of the muscle sarcomere, which could suggest these loci function as novel patterning factors. 

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