A quantitative gibberellin signaling biosensor reveals a role for gibberellins in internode specification at the shoot apical meristem.

Growth at the shoot apical meristem (SAM) is essential for shoot architecture construction. The phytohormones gibberellins (GA) play a pivotal role in coordinating plant growth, but their role in the SAM remains mostly unknown. Here, we developed a ratiometric GA signaling biosensor by engineering one of the DELLA proteins, to suppress its master regulatory function in GA transcriptional responses while preserving its degradation upon GA sensing.

Multi-Knock-a multi-targeted genome-scale CRISPR toolbox to overcome functional redundancy in plants.

Plant genomes are characterized by large and complex gene families that often result in similar and partially overlapping functions. This genetic redundancy severely hampers current efforts to uncover novel phenotypes, delaying basic genetic research and breeding programmes. Here we describe the development and validation of Multi-Knock, a genome-scale clustered regularly interspaced short palindromic repeat toolbox that overcomes functional redundancy in Arabidopsis by simultaneously targeting multiple gene-family members, thus identifying genetically hidden components.

Hormonal control of cell identity and growth in the shoot apical meristem.

How cells acquire their identities and grow coordinately within a tissue is a fundamental question to understand plant development. In angiosperms, the shoot apical meristem (SAM) is a multicellular tissue containing a stem cell niche, which activity allows for a dynamic equilibrium between maintenance of stem cells and production of differentiated cells that are incorporated in new aerial tissues and lateral organs produced in the SAM. Plant hormones are small-molecule signals controlling many aspects of plant development and physiology.

Live Imaging of Arabidopsis Axillary Meristems.

Axillary meristems (AMs) are established postembryonically at the leaf axils and can develop into lateral branches. The initiation of AMs establishes new growth axis and is of primary importance for understanding plant development. Understanding plant development requires live imaging of morphogenesis and gene expression.

A gene expression map of shoot domains reveals regulatory mechanisms.

Gene regulatory networks control development via domain-specific gene expression. In seed plants, self-renewing stem cells located in the shoot apical meristem (SAM) produce leaves from the SAM peripheral zone. After initiation, leaves develop polarity patterns to form a planar shape.

Patterning at the shoot apical meristem and phyllotaxis.

The shoot apical meristem (SAM) generates all above-ground organs throughout the life of plants. The development and maintenance of the SAM are crucial for building the plant architecture. The spatiotemporal patterning of lateral organs (leaves and flowers), called phyllotaxis, is one of the best-characterized self-organizing systems and has long been proposed to be driven by inhibitory fields generated by the existing organs and blocking new initiations in their vicinity.

Feedback from Lateral Organs Controls Shoot Apical Meristem Growth by Modulating Auxin Transport.

Stem cells must balance self-renewal and differentiation; thus, their activities are precisely controlled. In plants, the control circuits that underlie division and differentiation within meristems have been well studied, but those that underlie feedback on meristems from lateral organs remain largely unknown. Here we show that long-distance auxin transport mediates this feedback in a non-cell-autonomous manner.

Cytokinin Signaling Activates Expression during Axillary Meristem Initiation.

The homeodomain transcription factor WUSCHEL (WUS) defines the shoot stem cell niche, but the mechanisms underlying the establishment of expression remain unclear. Here, we show that cytokinin signaling precedes expression in leaf axils and activates expression de novo in the leaf axil to promote axillary meristem initiation. Furthermore, type-B Arabidopsis response regulator proteins, which are transcriptional activators in the cytokinin signaling pathway, directly bind to the promoter and activate its expression.

An organ boundary-enriched gene regulatory network uncovers regulatory hierarchies underlying axillary meristem initiation.

Gene regulatory networks (GRNs) control development via cell type-specific gene expression and interactions between transcription factors (TFs) and regulatory promoter regions. Plant organ boundaries separate lateral organs from the apical meristem and harbor axillary meristems (AMs). AMs, as stem cell niches, make the shoot a ramifying system.

AUXIN RESPONSE FACTOR 3 integrates the functions of AGAMOUS and APETALA2 in floral meristem determinacy.

In Arabidopsis, AUXIN RESPONSE FACTOR 3 (ARF3) belongs to the auxin response factor (ARF) family that regulates the expression of auxin-responsive genes. ARF3 is known to function in leaf polarity specification and gynoecium patterning. In this study, we discovered a previously unknown role for ARF3 in floral meristem (FM) determinacy through the isolation and characterization of a mutant of ARF3 that enhanced the FM determinacy defects of agamous (ag)-10, a weak ag allele.

The Stem Cell Niche in Leaf Axils Is Established by Auxin and Cytokinin in Arabidopsis.

Plants differ from most animals in their ability to initiate new cycles of growth and development, which relies on the establishment and activity of branch meristems harboring new stem cell niches. In seed plants, this is achieved by axillary meristems, which are established in the axil of each leaf base and develop into lateral branches. Here, we describe the initial processes of Arabidopsis thaliana axillary meristem initiation.