Since 1999, various forward- and reverse-genetic approaches have uncovered nearly 200 genes required for symbiotic nitrogen fixation (SNF) in legumes. These discoveries advanced our understanding of ...the evolution of SNF in plants and its relationship to other beneficial endosymbioses, signaling between plants and microbes, the control of microbial infection of plant cells, the control of plant cell division leading to nodule development, autoregulation of nodulation, intracellular accommodation of bacteria, nodule oxygen homeostasis, the control of bacteroid differentiation, metabolism and transport supporting symbiosis, and the control of nodule senescence. This review catalogs and contextualizes all of the plant genes currently known to be required for SNF in two model legume species,
and
, and two crop species,
(soybean) and
(common bean). We also briefly consider the future of SNF genetics in the era of pan-genomics and genome editing.
How genes shape diverse plant and animal body forms is a key question in biology. Unlike animal cells, plant cells are confined by rigid cell walls, and cell division plane orientation and growth ...rather than cell movement determine overall body form. The emergence of plants on land coincided with a new capacity to rotate stem cell divisions through multiple planes, and this enabled three-dimensional (3D) forms to arise from ancestral forms constrained to 2D growth. The genes involved in this evolutionary innovation are largely unknown. The evolution of 3D growth is recapitulated during the development of modern mosses when leafy shoots arise from a filamentous (2D) precursor tissue. Here, we show that a conserved, CLAVATA peptide and receptor-like kinase pathway originated with land plants and orients stem cell division planes during the transition from 2D to 3D growth in a moss, Physcomitrella. We find that this newly identified role for CLAVATA in regulating cell division plane orientation is shared between Physcomitrella and Arabidopsis. We report that roles for CLAVATA in regulating cell proliferation and cell fate are also shared and that CLAVATA-like peptides act via conserved receptor components in Physcomitrella. Our results suggest that CLAVATA was a genetic novelty enabling the morphological innovation of 3D growth in land plants.
•CLAVATA originated in the last common ancestor of land plants•CLAVATA regulates cell proliferation, fate, and growth in Physcomitrella•CLAVATA orients cell division planes in Physcomitrella and Arabidopsis•CLEs act via receptors that are conserved between Physcomitrella and Arabidopsis
Whitewoods, Cammarata, et al. show that a conserved CLAVATA (CLV) pathway arose in the last common ancestor of land plants. CLV regulates cell division plane orientation during the 2D to 3D growth transition in a moss, and roles for CLV are shared between mosses and flowering plants, suggesting that CLV enabled 3D growth to arise in land plants.
Summary
Autoregulation of nodulation (AON), a systemic signaling pathway in legumes, limits the number of nodules formed by the legume in its symbiosis with rhizobia. Recent research suggests a model ...for the systemic regulation in Medicago truncatula in which root signaling peptides are translocated to the shoot where they bind to a shoot receptor complex containing the leucine‐rich repeat receptor‐like kinase SUNN, triggering signal transduction which terminates nodule formation in roots. Here we show that a tagged SUNN protein capable of rescuing the sunn‐4 phenotype is localized to the plasma membrane and is associated with the plasmodesmata. Using bimolecular fluorescence complementation analysis we show that, like its sequence ortholog Arabidopsis CLV1, SUNN interacts with homologous CLV1‐interacting proteins MtCLAVATA2 and MtCORYNE. All three proteins were also able to form homomers and MtCRN and MtCLV2 also interact with each other. A crn Tnt1 insertion mutant of M. truncatula displayed a shoot controlled increased nodulation phenotype, similar to the clv2 mutants of pea and Lotus japonicus. Together these data suggest that legume AON signaling could occur through a multi‐protein complex and that both MtCRN and MtCLV2 may play roles in AON together with SUNN.
Significance Statement
Control of nodule number in legume roots is mediated by a receptor kinase that acts in the shoot, but how the signal is perceived in the shoot and transmitted to the roots is still unclear. Proteins that interact in local meristem signaling in Arabidopsis are shown here to interact with a kinase in the systemic nodulation signaling pathway in M. truncatula, suggesting that like the local pathway, the systemic pathway may coordinate multiple signals with different receptor/ligand combinations.
Cell division is often regulated by extracellular signaling networks to ensure correct patterning during development. In Arabidopsis, the SHORT-ROOT (SHR)/SCARECROW (SCR) transcription factor dimer ...activates CYCLIND6;1 (CYCD6;1) to drive formative divisions during root ground tissue development. Here, we show plasma-membrane-localized BARELY ANY MERISTEM1/2 (BAM1/2) family receptor kinases are required for SHR-dependent formative divisions and CYCD6;1 expression, but not SHR-dependent ground tissue specification. Root-enriched CLE ligands bind the BAM1 extracellular domain and are necessary and sufficient to activate SHR-mediated divisions and CYCD6;1 expression. Correspondingly, BAM-CLE signaling contributes to the restriction of formative divisions to the distal root region. Additionally, genetic analysis reveals that BAM-CLE and SHR converge to regulate additional cell divisions outside of the ground tissues. Our work identifies an extracellular signaling pathway regulating formative root divisions and provides a framework to explore this pathway in patterning and evolution.
Integration of genetic testing into routine oncology care could improve access to testing. This systematic review investigated interventions and the tailored implementation strategies aimed at ...increasing access to genetic counselling and testing and identifying hereditary cancer in oncology.
The search strategy results were reported using the PRISMA statement and four electronic databases were searched. Eligible studies included routine genetic testing for breast and ovarian cancer or uptake after universal tumour screening for colorectal or endometrial cancer. The titles and abstracts were reviewed and the full text articles screened for eligibility. Data extraction was preformed using a designed template and study appraisal was assessed using an adapted Newcastle Ottawa Scale. Extracted data were mapped to Proctor's et al outcomes and the Consolidated Framework for Implementation Research and qualitatively synthesised.
Twenty-seven studies, published up to May 2020, met the inclusion criteria. Twenty-five studies ranged from poor (72%), fair to good (28%) quality. Most interventions identified were complex (multiple components) such as; patient or health professional education, interdisciplinary practice and a documentation or system change. Forty-eight percent of studies with complex interventions demonstrated on average a 35% increase in access to genetic counselling and a 15% increase in testing completion. Mapping of study outcomes showed that 70% and 32% of the studies aligned with either the service and client or the implementation level outcome and 96% to the process or inner setting domains of the Consolidated Framework for Implementation Research.
Existing evidence suggests that complex interventions have a potentially positive effect towards genetic counselling and testing completion rates in oncology services. Studies of sound methodological quality that explore a greater breadth of pre and post implementation outcomes and informed by theory are needed. Such research could inform future service delivery models for the integration of genetics into oncology services.
BRAFV600E mutation in microsatellite-unstable (MSI) colorectal carcinomas (CRCs) virtually excludes Lynch syndrome (LS). In microsatellite-stable (MSS) CRCs it predicts poor prognosis. We propose a ...universal CRC LS screening algorithm using concurrent reflex immunohistochemistry (IHC) for BRAFV600E and mismatch-repair (MMR) proteins. We compared BRAFV600E IHC with multiplex polymerase chain reaction (PCR) and matrix-assisted laser desorption/ionization-time of flight mass spectrometry in 216 consecutive CRCs from 2011. Discordant cases were resolved with real-time PCR. BRAFV600E IHC was performed on 51 CRCs from the Australasian Colorectal Cancer Family Registry (ACCFR), which were fully characterized for BRAF mutation by allele-specific PCR, MMR status (MMR IHC and MSI), MLH1 promoter methylation, and germline MLH1 mutation. We then assessed MMR and BRAFV600E IHC on 1403 consecutive CRCs. By matrix-assisted laser desorption/ionization-time of flight mass spectrometry 15 cases did not yield a BRAF result, whereas 38/201 (19%) were positive. By IHC 45/216 (20%) were positive. Of the 7 discordant cases, real-time PCR confirmed the IHC result in 6. In the 51 CRCs from the ACCFR, IHC was concordant with allele-specific PCR in 50 cases. BRAFV600E and MSI IHC on 1403 CRCs demonstrated the following phenotypes: BRAF/MSS (1029 cases, 73%), BRAF/MSS (98, 7%), BRAF/MSI (183, 13%), and BRAF/MSI (93, 7%). All 11/1403 cancers associated with proven LS were BRAF/MSI. We conclude that BRAF IHC is highly concordant with 2 commonly used PCR-based BRAFV600E assays; it performed well in identifying MLH1 mutation carriers from the ACCFR and identified all cases of proven LS among the 1403 CRCs. Reflex BRAFV600E and MMR IHC are simple cheap tests that facilitate universal LS screening and identify the poor prognosis of the BRAFV600E-mutant MSS CRC phenotype.
"Mainstreaming" is a proposed strategy to integrate genomic testing into oncology. The aim of this paper is to develop a mainstreaming oncogenomics model by identifying health system interventions ...and implementation strategies for mainstreaming Lynch syndrome genomic testing.
A rigorous theoretical approach inclusive of conducting a systematic review and qualitative and quantitative studies was undertaken using the Consolidated Framework for Implementation Research. Theory-informed implementation data were mapped to the Genomic Medicine Integrative Research framework to generate potential strategies.
The systematic review identified a lack of theory-guided health system interventions and evaluation for Lynch syndrome and other mainstreaming programs. The qualitative study phase included 22 participants from 12 health organizations. The quantitative Lynch syndrome survey included 198 responses: 26% and 66% from genetic and oncology health professionals, respectively. Studies identified the relative advantage and clinical utility of mainstreaming to improve genetic test access and to streamline care, and adaptation of current processes was recognized for results delivery and follow-up. Barriers identified included funding, infrastructure and resources, and the need for process and role delineation. The interventions to overcome barriers were as follows: embedded mainstream genetic counselors, electronic medical record genetic test ordering, results tracking, and mainstreaming education resources. Implementation evidence was connected through the Genomic Medicine Integrative Research framework resulting in a mainstreaming oncogenomics model.
The proposed mainstreaming oncogenomics model acts as a complex intervention. It features an adaptable suite of implementation strategies to inform Lynch syndrome and other hereditary cancer service delivery. Implementation and evaluation of the model are required in future research.
Tissue culture transformation of plants has an element of art to it, with protocols passed on between labs but often not directly compared. As
has become popular as a model system for legumes, rapid ...transformation is critical, and many protocols exist, with varying results.
The
ecotypes, R108 and A17, were utilized to compare the effect of a modification to a previously used protocol based on shoot explants on the percentage of transformed plants produced from calli. This percentage was then compared to that of two additional transformation protocols based on root explants in the R108 ecotype. Variations in embryonic tissue sources, media components, time for transformation, and vectors were analyzed.
While no A17 transgenic plants were obtained, transgenic plantlets from the R108 ecotype were produced in as little as 4 months with a comparison of the two widely studied ecotypes under a single set of conditions. While the protocols tested gave similar results in percentage of transformed plants produced, considerations of labor and time to transgenics that vary between the root explant protocols tested were discovered. These considerations may influence which protocol to choose for introducing a single transgene versus creating lines with multiple mutations utilizing a CRISPR/Cas9 construct.
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