Root Development in Medicago truncatula: Lessons from Genetics to Functional Genomics

This decade introduced "omics" approaches, such as genomics, transcriptomics, proteomics, and metabolomics in association with reverse and forward genetic approaches, developed earlier, to try to identify molecular pathways involved in the development or in the response to environmental conditions as well as in animals and plants. This review summarizes studies that utilized "omics" strategies to unravel the root development in the model legume Medicago truncatula and how external factors such as soil mineral status or the presence of bacteria and fungi affect root system architecture in this species. We also compare these "omics" data to the knowledges concerning the Arabidopsis thaliana root development, nowadays considered as the model of allorhiz root systems. However, unlike legumes, this species is unable to interact with soil nitrogen-fixing rhizobia and arbuscular-mycorrhizal (AM) fungi to develop novel root-derived symbiotic structures. Differences in root organization, development, and regulatory pathways between these two model species have been highlighted.

Stable Inactivation of MicroRNAs in Medicago truncatula Roots

MicroRNAs are key regulators in the development processes or stress responses in plants. In the last decade, several conserved or non-conserved microRNAs have been identified in Medicago truncatula. Different strategies leading to the inactivation of microRNAs in plants have been described. Here, we propose a protocol for an effective inactivation of microRNAs using a STTM strategy in M. truncatula transgenic roots.

Functional PTB phosphate transporters are present in streptophyte algae and early diverging land plants

Two inorganic phosphate (Pi) uptake mechanisms operate in streptophytes and chlorophytes, the two lineages of green plants. PHOSPHATE TRANSPORTER B (PTB) proteins are hypothesized to be the Na⁺ /Pi symporters catalysing Pi uptake in chlorophytes, whereas PHOSPHATE TRANSPORTER 1 (PHT1) proteins are the H⁺ /Pi symporters that carry out Pi uptake in angiosperms. PHT1 proteins are present in all streptophyte lineages. However, Pi uptake in streptophyte algae and marine angiosperms requires Na⁺ influx, suggesting that Na⁺ /Pi symporters also function in some streptophytes. We tested the hypothesis that Na⁺ /Pi symporters exist in streptophytes. We identified PTB sequences in streptophyte genomes. Core PTB proteins are present at the plasma membrane of the liverwort Marchantia polymorpha. The expression of M. polymorpha core PTB proteins in the Saccharomyces cerevisiae pho2 mutant defective in high-affinity Pi transport rescues growth in low-Pi environments. Moreover, levels of core PTB mRNAs of M. polymorpha and the streptophyte alga Coleochaete nitellarum are higher in low-Pi than in Pi-replete conditions, consistent with a role in Pi uptake from the environment. We conclude that land plants inherited two Pi uptake mechanisms - mediated by the PTB and PHT1 proteins, respectively - from their streptophyte algal ancestor. Both systems operate in parallel in extant early diverging land plants.

The Mechanism Forming the Cell Surface of Tip-Growing Rooting Cells Is Conserved among Land Plants

To discover mechanisms that controlled the growth of the rooting system in the earliest land plants, we identified genes that control the development of rhizoids in the liverwort Marchantia polymorpha. 336,000 T-DNA transformed lines were screened for mutants with defects in rhizoid growth, and a de novo genome assembly was generated to identify the mutant genes. We report the identification of 33 genes required for rhizoid growth, of which 6 had not previously been functionally characterized in green plants. We demonstrate that members of the same orthogroup are active in cell wall synthesis, cell wall integrity sensing, and vesicle trafficking during M. polymorpha rhizoid and Arabidopsis thaliana root hair growth. This indicates that the mechanism for constructing the cell surface of tip-growing rooting cells is conserved among land plants and was active in the earliest land plants that existed sometime more than 470 million years ago [1, 2].

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336,000 T-DNA lines and a genome assembly were generated in Marchantia polymorpha

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33 genes required for rhizoid growth were identified

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Six of the 33 genes were functionally characterized in plants for the first time

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Genes belonging to these orthogroups were active in the first land plant roots

Identification of reference genes for real-time quantitative PCR experiments in the liverwort Marchantia polymorpha

Real-time quantitative polymerase chain reaction (qPCR) has become widely used as a method to compare gene transcript levels across different conditions. However, selection of suitable reference genes to normalize qPCR data is required for accurate transcript level analysis. Recently, Marchantia polymorpha has been adopted as a model for the study of liverwort development and land plant evolution. Identification of appropriate reference genes has therefore become a necessity for gene expression studies. In this study, transcript levels of eleven candidate reference genes have been analyzed across a range of biological contexts that encompass abiotic stress, hormone treatment and different developmental stages. The consistency of transcript levels was assessed using both geNorm and NormFinder algorithms, and a consensus ranking of the different candidate genes was then obtained. MpAPT and MpACT showed relatively constant transcript levels across all conditions tested whereas the transcript levels of other candidate genes were clearly influenced by experimental conditions. By analyzing transcript levels of phosphate and nitrate starvation reporter genes, we confirmed that MpAPT and MpACT are suitable reference genes in M. polymorpha and also demonstrated that normalization with an inappropriate gene can lead to erroneous analysis of qPCR data.

Strigolactones inhibit caulonema elongation and cell division in the moss Physcomitrella patens

In vascular plants, strigolactones (SLs) are known for their hormonal role and for their role as signal molecules in the rhizosphere. SLs are also produced by the moss Physcomitrella patens, in which they act as signaling factors for controlling filament extension and possibly interaction with neighboring individuals. To gain a better understanding of SL action at the cellular level, we investigated the effect of exogenously added molecules (SLs or analogs) in moss growth media. We used the previously characterized Ppccd8 mutant that is deficient in SL synthesis and showed that SLs affect moss protonema extension by reducing caulonema cell elongation and mainly cell division rate, both in light and dark conditions. Based on this effect, we set up bioassays to examine chemical structure requirements for SL activity in moss. The results suggest that compounds GR24, GR5, and 5-deoxystrigol are active in moss (as in pea), while other analogs that are highly active in the control of pea branching show little activity in moss. Interestingly, the karrikinolide KAR1, which shares molecular features with SLs, did not have any effect on filament growth, even though the moss genome contains several genes homologous to KAI2 (encoding the KAR1 receptor) and no canonical homologue to D14 (encoding the SL receptor). Further studies should investigate whether SL signaling pathways have been conserved during land plant evolution.

Strigolactones regulate protonema branching and act as a quorum sensing-like signal in the moss Physcomitrella patens

Strigolactones are a novel class of plant hormones controlling shoot branching in seed plants. They also signal host root proximity during symbiotic and parasitic interactions. To gain a better understanding of the origin of strigolactone functions, we characterised a moss mutant strongly affected in strigolactone biosynthesis following deletion of the CAROTENOID CLEAVAGE DIOXYGENASE 8 (CCD8) gene. Here, we show that wild-type Physcomitrella patens produces and releases strigolactones into the medium where they control branching of protonemal filaments and colony extension. We further show that Ppccd8 mutant colonies fail to sense the proximity of neighbouring colonies, which in wild-type plants causes the arrest of colony extension. The mutant phenotype is rescued when grown in the proximity of wild-type colonies, by exogenous supply of synthetic strigolactones or by ectopic expression of seed plant CCD8. Thus, our data demonstrate for the first time that Bryophytes (P. patens) produce strigolactones that act as signalling factors controlling developmental and potentially ecophysiological processes. We propose that in P. patens, strigolactones are reminiscent of quorum-sensing molecules used by bacteria to communicate with one another.

Femtosecond laser-assisted decagonal penetrating keratoplasty

PURPOSE

To assess the use of a new polygonal trephination pattern for penetrating keratoplasty (PK) assisted by femtosecond laser.

DESIGN

Prospective, nonrandomized clinical study.

METHODS

Sixteen eyes underwent decagonal PK. Nine had Fuchs dystrophy, 4 had pseudophakic bullous keratopathy, 1 had experienced trauma, 1 had corneal amyloidosis, and 1 had keratoconus. A Femtec (Tecnolas PerfectVision) laser was used to create decagonal penetrating cuts on both donor and recipient corneas. All patients were evaluated for uncorrected visual acuity, best spectacle-corrected visual acuity, pachymetry, topography, and endothelial cell density. Scanning electron microscopy was performed on corneal tissue after surgery.

RESULTS

All eyes were treated successfully without intraoperative complications. The mean follow-up ± standard deviation was 9.75 ± 3.5 months. Mean postoperative best spectacle-corrected visual acuity was 20/53, and there was a significant improvement in both uncorrected visual acuity (P = .0019) and best spectacle-corrected visual acuity (P = .001). At 6 months, mean ± standard deviation manifest astigmatism was 1.90 ± 1.20 diopters. Mean endothelial cell density was 1502 ± 458 cells/mm². Scanning electron microscopy displayed straight decagonal cut margins and minor remaining tissue bridges.

CONCLUSIONS

Use of the decagonal trephination profile was effective and safe to perform PK. Short-term visual results and refractive results are encouraging compared with those of conventional PK studies. Longer-term follow-up and comparative studies are necessary to determine precisely advantages the and optimal surgical settings of this technique.

[New therapeutic approach of keratoconus with intracorneal ring segments aided by femtosecond laser (Tecnolas Perfect Vision): indications, operating technique and results]

OBJECTIVE

To assess the results of intracorneal ring segment implantation assisted by the Tecnolas Perfect Vision(®) femtosecond laser (Heidelberg, Germany).

SETTINGS

Retrospective observational study.

METHODS

The patients were operated on with the Tecnolas Perfect Vision(®) femtosecond laser. The following parameters were evaluated before and after surgery: uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), corneal topography, wavefront analysis, and central corneal thickness. The Wilcoxon test was used for statistical analysis.

RESULTS

Seventeen eyes of 15 patients were included. The mean follow-up was 6.9±0.71 months. Significant improvement of UCVA and BCVA was observed in 82.35% (P=0.027) and 94.12% (P=0.003) of the eyes, respectively. The subjective refraction showed a significant decrease of the sphere from -10.29±5.54 to -6.5±5.03D (P=0.002). The subjective cylinder significantly decreased from 5.43±3.20 to 3.69±2.30D (P=0.026). The SAI also decreased significantly (P=0.011).

CONCLUSION

Femtosecond-assisted intracorneal ring segment implantation is an effective treatment for corneal ectasia. Further studies are needed to improve surgical parameters and outcomes.

[Anterior segment analysis using OCT3]

PURPOSE

Optical coherence tomography has been used for many years, in particular in the field of the retinal imaging, and is a promising technique in the analysis of the anterior segment, providing a similar resolution to histology for ocular tissue.

MATERIAL AND METHODS

We present a collection of images obtained with the OCT3 (Carl Zeiss Meditec, Dublin, CA), with parameters set to obtain good-quality images of the iris and corneal structures.

RESULTS

The OCT provides detailed analysis of the cornea, precise assessment of the dimensions and locations of corneal lesions - in the anterior-posterior plane as well as transversally or obliquely - with 10-microm precision, and the study of the iridocorneal angle and its dynamics.

DISCUSSION

Using the highly precise OCT3 for retinal imaging, it is possible to obtain good-quality anterior segment imaging, which makes the device highly versatile and thus increases reasons for acquiring this type of apparatus.

CONCLUSIONS

OCT3 users should not neglect this potential of the device, already in wide use for examining the retina.

Kératoplastie lamellaire antérieure assistée par laser femtoseconde

INTRODUCTION

Automated lamellar keratoplasty remains a challenging surgical technique because of surgical difficulties and is associated with a high rate of complications. The precision of the corneal cut at any corneal depth with the femtosecond laser is an important improvement in this technique. We report the first case of femtosecond-assisted anterior lamellar keratoplasty.

MATERIAL AND METHODS

A 63-year-old woman with anterior stromal dystrophy underwent femtosecond laser-assisted ALTK on the left eye. A donor lenticula was prepared from a corneoscleral rim utilizing the Femtec 20/10 Perfectvision femtosecond laser device and an artificial anterior chamber (Moria, Antony, France). The anterior lamellar cut was also performed on the patient's eye with the femtosecond laser.

RESULTS

Postoperative examinations showed a well-adapted graft with a clear interface. OCT III (Carl Zeiss Meditech, Dublin) measurements showed a corneal pachymetry of 713 microm associated with a regular posterior bed and a central thickness of 132 microm.

DISCUSSION

Femtosecond laser corneal cutting may offer greater safety, reproducibility, predictability, and flexibility. The risks of irregular cutting and microperforation are reduced. A better graft congruence can limit the risk of secondary displacement and the smooth interface should improve visual results.

CONCLUSION

Donor lenticulae and corneal cuttings performed with the Femtec 20/10 Perfectvision( femtosecond laser device can be used in the successful management of eyes requiring anterior lamellar keratoplasty. Further studies are needed to evaluate outcomes of this procedure.

[Bilateral corneal endothelial decompensation after postsepticemia coma]

We report a case of unexplained bilateral corneal endothelial decompensation after a coma. A 71-year-old man with no medical history presented with bilateral endothelial decompensation that required penetrating keratoplasty of the left eye combined with cataract surgery. This coma was caused by septicemia originally due to staphylococcus infection following catheter placement in preparation for a CT scan. Visual acuity of the left eye was 20/400 and 20/100 in the right eye when the patient awoke from the coma. After examination, we noted only stromal thickening and Descemet membrane folds causing corneal edema predominating OS. The rest of the exam was normal. Six months after surgery, visual acuity improved to 20/25. The most probable physiopathological mechanism of this decompensation is an iatrogenic complication from drugs administered during the patient's stay in intensive care (oxacillin), but we cannot rule out direct aggression of a bacterium or its toxin or the decompensation of a preexisting pathology.

[Teaching phacosection in a tropical setting]

PURPOSE

The aim of this study was to prospectively evaluate the training of a Malagasy ophthalmologist, already proficient in classic manual extracapsular cataract extraction (ECCE), in a small incision manual technique (phacosection).

MATERIALS AND METHODS

Within the activity of the Sight First program to fight blindness in Madagascar, the ophthalmologist of Majunga recruited patients presenting total white cataracts. These patients were operated by phacosection using the local hospital's usual instrumentation along with two specific phacosection instruments and extra single-use material (a precalibrated 3.2 mm knife and viscoelastic products). Peribulbar anesthesia with eye pressure was provided. Postoperative follow-up (visual acuity and corneal status) was conducted on days 1, 7 and 30.

RESULTS

Forty-four eyes were operated, the first seven by the instructor assisted by the local ophthalmologist, the next 36 by the local ophthalmologist assisted by the instructor. Five postoperative complications were noted: two cases of posterior capsular rupture (one during implantation) and three cases needing reoperation with aspiration of residual cortical masses. Induced astigmatism was low and visual rehabilitation was good, with all corneas clear at day 30.

DISCUSSION

The results are quite acceptable given the training period, with only two marked complications (one not related to the operative technique) and good visual rehabilitation in less than 2 weeks. This small incision technique allowed reduction of induced astigmatism and risk-free management of total white cataracts (independent of operator).

CONCLUSION

Small incision manual ECCE by phacosection is a safe, possible management option for difficult cataracts in a tropical setting with only a small increase in cost. Moreover, the training of an ophthalmologist mastering classic manual ECCE appears rapid and risk-free for patients.

Diffuse choroidal hemangioma: report of a clinicopathological study in a 4-year-old boy

The authors examined the clinicopathologic features of a 4-year-old boy with a diffuse choroidal hemangioma, yet without any features of the Sturge-Weber syndrome. The tumor occurred as a grayish intraocular mass with an overlying retinal detachment and was highly reflective in the ultrasonic examination. After contrast, the CT scan revealed diffuse thickening of the ocular wall associated with an enhanced irregular orbital mass. The pathologic examination revealed a cavernous hemangioma involving the entire choroid with extrascleral extension. Diffuse choroidal hemangioma occurring in childhood and unrelated to the Sturge-Weber syndrome is a rare condition that should be included in the differential diagnosis of retinoblastoma.