Repression of Floral Meristem Fate Is Crucial in Shaping Tomato Inflorescence

Tomato is an important crop and hence there is a great interest in understanding the genetic basis of its flowering. Several genes have been identified by mutations and we constructed a set of novel double mutants to understand how these genes interact to shape the inflorescence. It was previously suggested that the branching of the tomato inflorescence depends on the gradual transition from inflorescence meristem (IM) to flower meristem (FM): the extension of this time window allows IM to branch, as seen in the compound inflorescence (s) and falsiflora (fa) mutants that are impaired in FM maturation. We report here that JOINTLESS (J), which encodes a MADS-box protein of the same clade than SHORT VEGETATIVE PHASE (SVP) and AGAMOUS LIKE 24 (AGL24) in Arabidopsis, interferes with this timing and delays FM maturation, therefore promoting IM fate. This was inferred from the fact that j mutation suppresses the high branching inflorescence phenotype of s and fa mutants and was further supported by the expression pattern of J, which is expressed more strongly in IM than in FM. Most interestingly, FA - the orthologue of the Arabidopsis LEAFY (LFY) gene - shows the complementary expression pattern and is more active in FM than in IM. Loss of J function causes premature termination of flower formation in the inflorescence and its reversion to a vegetative program. This phenotype is enhanced in the absence of systemic florigenic protein, encoded by the SINGLE FLOWER TRUSS (SFT) gene, the tomato orthologue of FLOWERING LOCUS T (FT). These results suggest that the formation of an inflorescence in tomato requires the interaction of J and a target of SFT in the meristem, for repressing FA activity and FM fate in the IM

The xerobranching response represses lateral root formation when roots are not in contact with water

Efficient soil exploration by roots represents an important target for crop improvement and food security [1, 2]. Lateral root (LR) formation is a key trait for optimising soil foraging for crucial resources such as water and nutrients. Here, we report an adaptive response termed xerobranching, exhibited by cereal roots, that represses branching when root tips are not in contact with wet soil. Non-invasive X-ray microCT imaging revealed that cereal roots rapidly repress LR formation as they enter an air space within a soil profile and are no longer in contact with water. Transcript profiling of cereal root tips revealed that transient water deficit triggers the abscisic acid (ABA) response pathway. In agreement with this, exogenous ABA treatment can mimic repression of LR formation under transient water deficit. Genetic analysis in Arabidopsis revealed that ABA repression of LR formation requires the PYR/PYL/RCAR-dependent signalling pathway. Our findings suggest that ABA acts as the key signal regulating xerobranching. We conclude that this new ABA-dependent adaptive mechanism allows roots to rapidly respond to changes in water availability in their local micro-environment and to use internal resources efficiently

The xerobranching response represses lateral root formation when roots are not in contact with water

Efficient soil exploration by roots represents an important target for crop improvement and food security [1, 2]. Lateral root (LR) formation is a key trait for optimising soil foraging for crucial resources such as water and nutrients. Here, we report an adaptive response termed xerobranching, exhibited by cereal roots, that represses branching when root tips are not in contact with wet soil. Non-invasive X-ray microCT imaging revealed that cereal roots rapidly repress LR formation as they enter an air space within a soil profile and are no longer in contact with water. Transcript profiling of cereal root tips revealed that transient water deficit triggers the abscisic acid (ABA) response pathway. In agreement with this, exogenous ABA treatment can mimic repression of LR formation under transient water deficit. Genetic analysis in Arabidopsis revealed that ABA repression of LR formation requires the PYR/PYL/RCARdependent signalling pathway. Our findings suggest that ABA acts as the key signal regulating xerobranching. We conclude that this new ABA-dependent adaptive mechanism allows roots to rapidly respond to changes in water availability in their local micro-environment and to use internal resources efficiently

Critically evaluating collaborative research: why is it difficult to extend truth tests to reality tests?

We argue that critical evaluation achieves the reflexivity needed to facilitate collaboration by proposing boundary-negotiating artefacts to configure a joint action domain. Those objects become mediators for innovation by triggering controversies, conceived preventatively via an organized extension of what Boltanski calls ‘truth tests’ to ‘reality tests’ so that they dynamize ongoing affairs. However, critical evaluation must also anticipate actors’ reappropriation of boundary-negotiating artefacts in the effort to protect their rights, stakes or room for manoeuvre. Three scenarios commonly arise: avoidance or utopian projecting, enactment of inverted reality tests, and disavowal through role exchange. The article develops these propositions through the reconstruction of a modified theory-based evaluation of a collaborative research programme. The programme set out to explore how evidence from health research could be used rapidly and effectively in the context of practical problems and organizational challenges, so an internal evaluation was set up to facilitate learning during the process. What ensued, however, was a loss of trust between partners, resolved only by repositioning the evaluation as a reflective academic study, reducing its reflexive capacity to intervene on the level of activity and organizational integration. We conclude that doing successful critical evaluation and, more generally, achieving political pertinence for social scientific discourses depends on creating the conditions in which actors are able to take the risks and share the costs associated with the enhanced level of reflexivity necessary to engage in collective action as well as knowledge production

Effets du froid sur les stades précoces de développement du maïs (Zea mays L.) (synthèse bibliographique)

Effects of cold temperatures on the early stages of maize (Zea mays L.). A review. Introduction. Maize is a crop of great economical importance. Despite its tropical origin and its high sensitivity to low temperatures, maize is now cultivated in a wide range of latitudes. To maintain competitive yields, many genetic and agricultural adaptations have been implemented. Literature. Plant responses to environmental stresses such as drought or cold have been extensively studied. This article reviews the progress and current knowledge regarding the effects of non-freezing cold temperatures on maize plants, from germination to floral transition. During the early stages of development, cold alters plant phenology and productivity, mainly because of its negative impact on photosynthesis. Plant growth is affected and secondary osmotic and oxidative stresses induce cell damage. Conclusion. A better understanding of the effects of cold will allow the development of new strategies for improving plant tolerance through the use of various physiological, genetic and molecular approaches

Gibberellins and the floral transition in Sinapis alba

peer reviewedThe putative role of gibberellins in the transition to flowering was investigated in Sinapis alba, a caulescent long-day (LD) plant. It was observed that: (1) physiological doses of exogenous gibberellins (GA(1), GA(3), GA(9)) do not cause the floral shift of the meristem when applied to plants grown in short days but have some positive effect on the flowering response to a suboptimal LD; no inhibition was observed in any case; (2) GA-biosynthesis inhibitors (prohexadione-Ca and paclobutrazol) considerably inhibit stem growth but have some negative effect on flowering only when a suboptimal LD is given; and (3) the floral transition induced by one 22-h LD does not correlate with any detectable change in GA content of the apical bud, of the leaves, and of the phloem exudate reaching the apex. Taken together, these results suggest that GAs do not act as a major signal for photoperiodic flower induction in Sinapis

UNIFLORA, a pivotal gene that regulates floral transition and meristem identity in tomato (Lycopersicon esculentum)

Flowering of uniflora (uf), a tomato (Lycopersicon esculentum) mutant which consistently produces solitary flowers instead of inflorescences, is late and highly asynchronous in winter. This puzzling behaviour prompted us to further investigate flowering regulation in this mutant to improve our understanding of UNIFLORA gene function. Growing plants under different daylengths and light intensities revealed that flowering time in uf is dependent on daily light energy integral. Transferring plants from low to high light energy integrals at different times after sowing showed that the light-conditions effect was stage dependent, suggesting that interactions between light energy integrals and endogenous regulatory pathways affect meristem sensitivity to flowering signals. Carbohydrate analyses suggested that one of these signals could be sucrose, but other interacting factors are probably generated by the root system, as indicated by grafting experiments. The UNIFLORA gene thus appears to have a dual role in tomato: floral transition regulation and the maintenance of inflorescence meristem identity