Transcriptional reprogramming during floral fate acquisition

Coordinating growth and patterning is essential for eukaryote morphogenesis. In plants, auxin is a key regulator of morphogenesis implicated throughout development. Despite this central role, our understanding of how auxin coordinates cell fate and growth changes is still limited. Here, we addressed this question using a combination of genomic screens to delve into the transcriptional network induced by auxin at the earliest stage of flower development, prior to morphological changes. We identify a shoot-specific network suggesting that auxin initiates growth through an antagonistic regulation of growth-promoting and growth-repressive hormones, quasi-synchronously to floral fate specification. We further identify two DNA-binding One Zinc Finger (DOF) transcription factors acting in an auxin-dependent network that could interface growth and cell fate from the early stages of flower development onward.Peer reviewe

A Light-Regulated Genetic Module Was Recruited to Carpel Development in Arabidopsis following a Structural Change to SPATULA

A key innovation of flowering plants is the female reproductive organ, the carpel. Here, we show that a mechanism that regulates carpel margin development in the model flowering plant Arabidopsis thaliana was recruited from light-regulated processes. This recruitment followed the loss from the basic helix-loop-helix transcription factor SPATULA (SPT) of a domain previously responsible for its negative regulation by phytochrome. We propose that the loss of this domain was a prerequisite for the light-independent expression in female reproductive tissues of a genetic module that also promotes shade avoidance responses in vegetative organs. Striking evidence for this proposition is provided by the restoration of wild-type carpel development to spt mutants by low red/far-red light ratios, simulating vegetation shade, which we show to occur via phytochrome B, PHYTOCHROME INTERACTING FACTOR4 (PIF4), and PIF5. Our data illustrate the potential of modular evolutionary events to generate rapid morphological change and thereby provide a molecular basis for neo-Darwinian theories that describe this nongradualist phenomenon. Furthermore, the effects shown here of light quality perception on carpel development lead us to speculate on the potential role of light-regulated mechanisms in plant organs that, like the carpel, form within the shade of surrounding tissues

Overexpression of the arabidopsis thaliana signalling peptide TAXIMIN1 affects lateral organ development

International audienceLateral organ boundary formation is highly regulated by transcription factors and hormones such as auxins and brassinosteroids. However, in contrast to many other developmental processes in plants, no role for signalling peptides in the regulation of this process has been reported yet. The first characterization of the secreted cysteine-rich TAXIMIN (TAX) signalling peptides in Arabidopsis is presented here. TAX1 overexpression resulted in minor alterations in the primary shoot and root metabolome, abnormal fruit morphology, and fusion of the base of cauline leaves to stems forming a decurrent leaf attachment. The phenotypes at the paraclade junction match TAX1 promoter activity in this region and are similar to loss of LATERAL ORGAN FUSION (LOF) transcription factor function. Nevertheless, TAX1 expression was unchanged in lof1lof2 paraclade junctions and, conversely, LOF gene expression was unchanged in TAX1 overexpressing plants, suggesting TAX1 may act independently. This study identifies TAX1 as the first plant signalling peptide influencing lateral organ separation and implicates the existence of a peptide signal cascade regulating this process in Arabidopsis

Dissecting the pathways coordinating patterning and growth by plant boundary domains.

Boundary domains play important roles during morphogenesis in plants and animals, but how they contribute to patterning and growth coordination in plants is not understood. The CUC genes determine the boundary domains in the aerial part of the plants and, in particular, they have a conserved role in regulating leaf complexity across Angiosperms. Here, we used tooth formation at the Arabidopsis leaf margin controlled by the CUC2 transcription factor to untangle intertwined events during boundary-controlled morphogenesis in plants. Combining conditional restoration of CUC2 function with morphometrics as well as quantification of gene expression and hormone signaling, we first established that tooth morphogenesis involves a patterning phase and a growth phase. These phases can be separated, as patterning requires CUC2 while growth can occur independently of CUC2. Next, we show that CUC2 acts as a trigger to promote growth through the activation of three functional relays. In particular, we show that KLUH acts downstream of CUC2 to modulate auxin response and that expressing KLUH can compensate for deficient CUC2 expression during tooth growth. Together, we reveal a genetic and molecular network that allows coordination of patterning and growth by CUC2-defined boundaries during morphogenesis at the leaf margin

From spatio-temporal morphogenetic gradients to rhythmic patterning at the shoot apex

A key question in developmental biology is how morphogenetic regulators control patterning. Recent findings have raised an important question: do morphogenetic signals carry information not only in space, as originally proposed in the morphogen concept, but also in time? The hormone auxin is an essential plant morphogenetic regulator that drives rhythmic organogenesis at the shoot apical meristem. Here, we used a quantitative imaging approach to map auxin distribution and response. We demonstrate the existence of high-definition spatio-temporal auxin distribution in the meristem. We provide evidence that developing organs are auxin-emitting centers that could allow self-sustained distribution of auxin through a structured auxin transport network converging on the meristem center. We finally demonstrate that regulation of histone acetylation allows cells to measure the duration of the exposition to auxin preceding organ initiation, providing a remarkable example of how both spatial and temporal morphogenetic information generates rhythmic patterning

Root-knot nematode (Meloidogyne spp.) Me resistance genes in pepper (Capsicum annuum L.) are clustered on the P9 chromosome

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Mapping of the dominant Me genes cluster conferring resistance to root-knot nematodes in pepper (Capsicum annuum L.)

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Halotropism Is a Response of Plant Roots to Avoid a Saline Environment

International audienceTropisms represent fascinating examples of how plants respond to environmental signals by adapting their growth and development. Here, a novel tropism is reported, halotropism, allowing plant seedlings to reduce their exposure to salinity by circumventing a saline environment. In response to a salt gradient, Arabidopsis, tomato, and sorghum roots were found to actively prioritize growth away from salinity above following the gravity axis. Directionality of this response is established by an active redistribution of the plant hormone auxin in the root tip, which is mediated by the PIN-FORMED 2 (PIN2) auxin efflux carrier. We show that salt-induced phospholipase D activity stimulates clathrin-mediated endocytosis of PIN2 at the side of the root facing the higher salt concentration. The intracellular relocalization of PIN2 allows for auxin redistribution and for the directional bending of the root away from the higher salt concentration. Our results thus identify a cellular pathway essential for the integration of environmental cues with auxin-regulated root growth that likely plays a key role in plant adaptative responses to salt stress