The founder-cell transcriptome in the Arabidopsis apetala1 cauliflower inflorescence meristem.

Anneke Frerichs,Rahere Thoma,Ali Taleb Abdallah,Wolfgang Werr,John William Chandler,Peter Frommolt

doi:10.1186/s12864-016-3189-x

Abstract

BackgroundAlthough the pattern of lateral organ formation from apical meristems establishes species-specific plant architecture, the positional information that confers cell fate to cells as they transit to the meristem flanks where they differentiate, remains largely unknown. We have combined fluorescence-activated cell sorting and RNA-seq to characterise the cell-type-specific transcriptome at the earliest developmental time-point of lateral organ formation using DORNRÖSCHEN-LIKE::GFP to mark founder-cell populations at the periphery of the inflorescence meristem (IM) in apetala1 cauliflower double mutants, which overproliferate IMs.ResultsWithin the lateral organ founder-cell population at the inflorescence meristem, floral primordium identity genes are upregulated and stem-cell identity markers are downregulated. Additional differentially expressed transcripts are involved in polarity generation and boundary formation, and in epigenetic and post-translational changes. However, only subtle transcriptional reprogramming within the global auxin network was observed.ConclusionsThe transcriptional network of differentially expressed genes supports the hypothesis that lateral organ founder-cell specification involves the creation of polarity from the centre to the periphery of the IM and the establishment of a boundary from surrounding cells, consistent with bract initiation. However, contrary to the established paradigm that sites of auxin response maxima pre-pattern lateral organ initiation in the IM, auxin response might play a minor role in the earliest stages of lateral floral initiation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3189-x) contains supplementary material, which is available to authorized users.

Highlights

The pattern of lateral organ formation from apical meristems establishes species-specific plant architecture, the positional information that confers cell fate to cells as they transit to the meristem flanks where they differentiate, remains largely unknown
That the combined use of fluorescence-activated cell sorting (FACS)/RNA sequencing (RNA-seq) is suitable to address cellular decisions in the shoot apical meristem (SAM) at a resolution not previously achieved
Isolation of DRNL::GFP-expressing cells from ap1 cal inflorescence apices The cauliflower inflorescence phenotype of the ap1 cal double mutant (Fig. 1a) results from the initiation of lateral meristems at the inflorescence meristem (IM) periphery that retain IM identity and initiate secondary or tertiary IM meristems in a spiral phyllotaxy, which is revealed by imaging of the lateral organ founder-cell (LOFC) marker DRNL::GFP (Fig. 1b)

Summary

Introduction

The pattern of lateral organ formation from apical meristems establishes species-specific plant architecture, the positional information that confers cell fate to cells as they transit to the meristem flanks where they differentiate, remains largely unknown. We have combined fluorescence-activated cell sorting and RNA-seq to characterise the cell-type-specific transcriptome at the earliest developmental time-point of lateral organ formation using DORNRÖSCHEN-LIKE::GFP to mark founder-cell populations at the periphery of the inflorescence meristem (IM) in apetala cauliflower double mutants, which overproliferate IMs. The development of the aerial plant body depends on the activity of the shoot apical meristem (SAM), whereby pluripotent stem cells transit from the central stem-cell zone towards the periphery and become specified as lateral organ founder cells (LOFCs) depending on their precise position. Bract development in lfy and puchi mutants disrupts the unidirectional sequence of firstwhorl floral organ initiation of wild type [6], which suggests a complex developmental dynamism of founder-cell specification and overlapping positional information for the abaxial sepal and bract in the wild type IM. LOFC specification in the outer floral whorl of sepals occurs in the absence of stem-cell markers such as CLAVATA3 (CLV3) or WUSCHEL (WUS) at the IM periphery, which regain activity after initation of the abaxial sepal, when a furrow separates the stage 2 primordium from the IM [7, 8]

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Conclusion