Reflections on the triptych of meristems that build flowering branches in tomato

peer reviewedBranching is an important component determining crop yield. In tomato, the sympodial pattern of shoot and inflorescence branching is initiated at floral transition and involves the precise regulation of three very close meristems: i) the shoot apical meristem (SAM) that undergoes the first transition to flower meristem (FM) fate, ii) the inflorescence sympodial meristem (SIM) that emerges on its flank and remains transiently indeterminate to continue flower initiation, and iii) the shoot sympodial meristem (SYM), which is initiated at the axil of the youngest leaf primordium and takes over shoot growth before forming itself the next inflorescence. The proper fate of each type of meristems involves the spatiotemporal regulation of FM genes, since they all eventually terminate in a flower, but also the transient repression of other fates since conversions are observed in different mutants. In this paper, we summarize the current knowledge about the genetic determinants of meristem fate in tomato and share the reflections that led us to identify sepal and flower abscission zone initiation as a critical stage of FM development that affects the branching of the inflorescence

LED Color Gradient As A New Screening Tool For Rapid Phenotyping Of Plant Responses To Light Quality

Background The increasing demand for local food production is fueling high interest in the development of controlled environment agriculture. In particular, LED technology brings energy-saving advantages together with the possibility to manipulate plant phenotypes through light quality control. However, optimizing light quality is required for each cultivated plant and specific purpose. Findings In this paper, it is shown that the combination of LED gradient setups with imaging-based non-destructive plant phenotyping constitutes an interesting new screening tool with the potential to improve speed, logistics, and information output. To validate this concept, an experiment was performed to evaluate the effects of a complete range of Red:Blue ratios on seven plant species: Arabidopsis thaliana, Brachypodium distachyon, Euphorbia peplus, Ocimum basilicum, Oryza sativa, Solanum lycopersicum, and Setaria viridis. Plants were exposed during 30 days to the light gradient and showed significant, but species-dependent, responses in terms of dimension, shape, and color. A time series analysis of phenotypic descriptors highlighted growth changes but also transient responses of plant shapes to the Red:Blue ratio. Conclusion This approach, which generated a large reusable dataset, can be adapted for addressing specific needs in crop production or fundamental questions in photobiology.VeLire, Tropical Plant Factory (Plant'HP

Role of compliance in Helicobacter pylori eradication treatment : Results of the European Registry on H. pylori management

Peer reviewe

Role of the tomato JOINTLESS gene in inflorescence develoment

Tomato is an important crop worldwide and knowledge about the genetic determinants of its yield is highly valuable for further improvement. The plant has a sympodial shoot architecture, producing about 6 to 12 leaves on the primary stem before the shoot apical meristem (SAM) terminates with an inflorescence; further growth then occurs from a sympodial shoot meristem (SYM) hosted at the axil of the uppermost leaf that forms a sympodial unit of usually 3 leaves and the next inflorescence. The inflorescence of tomato is a monochasial cyme: the apical meristem (the SAM in the primary shoot and the SYM in the sympodial units) is converted to a flower meristem (FM) and inflorescence growth continues from a lateral meristem (the inflorescence sympodial meristem, SIM), which “maturates” towards FM identity and forms a subsequent lateral SIM that repeats the process. Understanding the regulation of flowering time and inflorescence development in tomato has much progressed thanks to the characterization of loss-of function-mutants and functional analyses of the identified genes. This thesis is focused on one of these mutants: jointless (j), which was initially isolated because it lacks the abscission zone (AZ) in fruit pedicel. However, the inflorescences of j mutants return to leaf initiation after the formation of few flowers, indicating that the J gene also plays a role in the development of the inflorescence. J encodes a MADS-box protein of the AGAMOUS LIKE 24 (AGL24)/SHORT VEGETATIVE PHASE (SVP) subfamily. Previous research led to the hypothesis that J plays a dual role in the development of the inflorescence, avoiding the reversion of SIMs to a vegetative fate, which would lead to leaf initiation as observed in j mutant, and preventing their early maturation to FM fate, which would lead to fast termination of the inflorescence. However the molecular bases of J function remained to be elucidated. The aim of this thesis was to unravel the roles of J, trying to clarify its mode of action, the genes impacted by its expression and how its suppression leads to a leafy inflorescence phenotype. To achieve this goal, we used different approaches. First of all, a detailed phenotyping of j mutants was performed. The genetic backgrounds of the mutants differed in their sympodial shoot growth that was either indeterminate (due to the expression of SELF PRUNING (SP) gene, a repressor of flowering, in the SYM) or determinate (sp mutants). We observed that the leafy inflorescence phenotype of the j mutants was stronger in indeterminate backgrounds, indicating a functional link between J and SP. All mutants showed a slight delay of flowering (1 or 2 additional leaves). Secondly, a transcriptomic analysis (RNA-seq) of the ultimate and penultimate meristems of young inflorescences of j mutants in an indeterminate (Ailsa Craig, AC) and a determinate (Heinz, Hz) backgrounds confirmed the functional link between J and SP. We indeed found that j mutation causes very little transcriptomic changes in sp background (Hz) whereas j mutation leads to SP activation in the inflorescences of j(AC) mutant, indicating that its leafy phenotype is due to the activation of SYM fate in place of a SIM. The transcriptome of j(AC) also revealed the up-regulation of MADS-box genes involved in flower organ identity (homeotic genes of B- and C-classes). These changes might explain that, in addition to leafy inflorescences, j(AC) mutants have reduced inflorescences terminating early after the formation of 2-3 flowers. Most interestingly, the RNA-seq analysis also revealed that a regulatory network involved in shoot branching, comprising BRANCHED1 (BRC1) and components of physiological signaling by trehalose phosphate and hormones, is active in the inflorescence of tomato

Architectural and developmental changes due to overexpression of the JOINTLESS gene in tomato

Inflorescence architecture shows huge variation among flowering plants, especially in the amount of flowers and branching degree. In tomato, the formation of the inflorescence follows a sympodial pattern : the shoot apical meristem (SAM) acquires a floral meristem (FM) fate and forms the first flower while a lateral inflorescence meristem (IM) is initiated, which itself matures into a FM when a second IM is initiated, and so on. This sympodial mode of inflorescence development is regulated by a complex genetic network, which remains to be elucidated. Tomato is also used as a model in the study of abscission, an important process by which plants can isolate and drop different parts such as non fertilized flowers, damaged organs or ripe fruits. The lack of fruit abscission zone – the “jointless” phenotype – is associated with the j and j-2 mutations, which impair the function of two MADS-box genes: JOINTLESS (J) and SlMBP21. We are interested in understanding the functions of J, because j knock-out mutation does not only alter the abscission zone but causes inflorescence reversion to leaf production after the initiation of few flowers. Our goal is therefore to identify the targets of J by different molecular approaches.Study of jointless gene in the inflorecence architecture of tomat

Overexpression of the tomato JOINTLESS gene alters flowering

Abscission is an important mechanism that allows plants to separate unfertilized flowers, ripe fruits or damage organs from the plant. In tomato, jointless (j) and jointless-2 (j-2) mutations leads a lack of abscission zone (AZ) in the flower pedicel, which will avoid falling of ripe fruits and prevent loss of yield. Both J and J-2 are genes encoding MADS-box transcription factors (Mao et al. 2000; Gomez-Roldan et al., 2017) that can interact with other MADS-box proteins, like MACROCALYX (MC), forming a multimeric complex able to regulate the AZ formation (Liu et al. 2014). In addition to the AZ formation, J also plays a role in flowering architecture and meristem fate. This last role is consistent with the functions of the closets homologs of J in Arabidopsis, SHORT VEGETATIVE PHASE (SVP) and AGAMOUS LIKE 24 (AGL24) (Gregis et al. 2006). Mutation of J leads to a faster flower maturation and a reversion to the vegetative state of the inflorescence meristems, which originates leafy inflorescences (Périlleux et al. 2014). Nevertheless, J is not the only one that regulates at the same time AZ formation and meristem functions. Other transcription factors such as the tomato homolog of WUSHEL (LeWUS), GOBLET (GOB), LATERAL SUPPRESSOR (Ls) and Blind (Bl) are involved in those pathways (Nakano et al. 2012; Nakano et al. 2013). We have generated transgenic plants that overexpress J (35S:J) showing changes in the inflorescence architecture and AZ development, but also having interesting phenotypes in axillary development and leaf complexity. These results suggest that J takes part in different pathways and regulate several downstream genes. Our goal is to identify and study the targets of the J transcription factor in order to understand its functions in the tomato plant

Natural and induced loss of function mutations in SlMBP21 MADS-box gene led to jointless-2 phenotype in tomato

Abscission is the mechanism by which plants disconnect unfertilized flowers, ripe fruits, senescent or diseased organs from the plant. In tomato, pedicel abscission is an important agronomic factor that controls yield and post-harvest fruit quality. Two non-allelic mutations, jointless (j) and jointless-2 (j-2), controlling pedicel abscission zone formation have been documented but only j-2 has been extensively used in breeding. J was shown to encode a MADS-box protein. Using a combination of physical mapping and gene expression analysis we identified a positional candidate, Solyc12g038510, associated with j-2 phenotype. Targeted knockout of Solyc12g038510, using CRISPR/Cas9 system, validated our hypothesis. Solyc12g038510 encodes the MADS-box protein SlMBP21. Molecular analysis of j-2 natural variation revealed two independent loss-of-function mutants. The first results of an insertion of a Rider retrotransposable element. The second results of a stop codon mutation that leads to a truncated protein form. To bring new insights into the role of J and J-2 in abscission zone formation, we phenotyped the single and the double mutants and the engineered alleles. We showed that J is epistatic to J-2 and that the branched inflorescences and the leafy sepals observed in accessions harboring j-2 alleles are likely the consequences of linkage drags

Analysing the molecular and phenotypic effects of overexpression of JOINTLESS gene in tomato

JOINTLESS (J) is a MADS-box gene that regulates inflorescence traits in tomato: its mutation reduces the number of flowers in the inflorescence, which reverts to leaf initiation, and suppresses the abscission zone (AZ) in the flower pedicels. It has been shown that the J protein physically interacts with other MADS-box transcription factors, MACROCALYX (MC) and JOINTLESS-2 (J-2) previously known as SlMBP21. Their putative targets are genes involved in AZ initiation since j, j-2 and mc mutants share this common phenotype. For a better understanding of the role of J in the architecture of the inflorescence, overexpression lines have been generated. A RNA-seq approach, comparing overexpression and wild-type lines, has been used to identify potential J-targets and better understand its molecular function

LED light gradient as a screening tool for light quality responses in model plant species

Current developments in light-emitting diodes (LEDs) technologies have opened new perspectives for sustainable and highly efficient indoor cultivation. The introduction of LEDs not only allows a reduction in the production costs on a quantitative level, it also offers opportunities to manipulate and optimise qualitative traits. Indeed, while plants respond strongest to red and blue lights for photosynthesis, the whole light spectrum has an effect on plant shape, development, and chemical composition. In order to evaluate LEDs as an alternative to traditional lighting sources, the species-specific plant responses to distinct wavelengths need to be evaluated under controlled conditions. Here, we tested the possibility to use light composition gradients in combination with semi-automated phenotyping to rapidly explore the phenotypic responses of different species to variations in the light spectrum provided by LED sources. Plants of seven different species (Arabidopsis thaliana, Ocimum basilicum, Solanum lycopersicum, Brachypodium distachyon, Oryza sativa, Euphorbia peplus, Setaria viridis) were grown under standard white fluorescent light for 30 days, then transferred to a Red:Blue gradient for another 30 days and finally returned to white light. In all species, differences in terms of dimension, shape, and color were rapidly observed across the gradient and the overall response was widely species-dependent. The experiment yielded large amounts of imaging-based phenotypic data and we suggest simple data analysis methods to aggregate the results and facilitate comparisons between species. Similar experimental setups will help achieve rapid environmental optimization, screen new crop species and genotypes, or develop new gene discovery strategies

Towards understanding the function of JOINTLESS gene in tomato inflorescence

The lack of fruit abscission is a trait of great agronomical value. In tomato, the jointless phenotype, referring to the lack of abscission zone (AZ) in the flower pedicel, has been obtained by two independent mutations, named jointless (j) and jointless-2 (j-2). The corresponding genes encode MADS-box transcription factors, as shown in 2000 for J (Mao et al. 2000) and very recently for J-2, known as SlMBP21 (Gomez-Roldan et al., 2017). Similar to the quartet model of MADS-box protein complexes regulating floral organ formation, J and J-2 interact with MADS-box partners, among which MACROCRALYX (MC), to regulate AZ formation (Liu et al. 2014). In addition to - or in connection with - AZ formation, J acts during the building of the inflorescence to regulate meristem fate. Indeed j mutants produce leafy inflorescences characterized by faster flower maturation and resumption of vegetative meristems (Périlleux et al. 2014). For these traits, j is epistatic to j-2. The involvement of J in the regulation of meristem fate is consistent with the roles of its closest homologs in Arabidopsis, AGAMOUS LIKE 24 (AGL24) and SHORT VEGETATIVE PHASE (SVP). Our goal is to identify J targets in order to unravel its multiple functions in the tomato inflorescence