Abstract
The intrusive growth, a type of plant cell elongation occurring in the depths of plant tissues, is characterized by the invasion of a growing cell between its neighbours due to a higher rate of elongation. In order to reveal the largely unknown molecular mechanisms of intrusive growth, we isolated primary flax phloem fibers specifically at the stage of intrusive growth by laser microdissection. The comparison of the RNA-Seq data from several flax stem parts enabled the characterization of those processes occurring specifically during the fiber intrusive elongation. The revealed molecular players are summarized as those involved in the supply of assimilates and support of turgor pressure, cell wall enlargement and modification, regulation by transcription factors and hormones, and responses to abiotic stress factors. The data obtained in this study provide a solid basis for developing approaches to manipulate fiber intrusive elongation, which is of importance both for plant biology and the yield of fiber crops.
Highlights
The fiber intrusive elongation is very important for the development of plant architecture as well as for the yield and quality of commercial plant fibers[6,7,10]
To obtain a full picture of the genes expressed during the intrusive growth of fibers in planta, we performed a comparative RNA-Seq analysis with the mRNAs isolated from the apical part of the stem (APEX) and the intrusively growing phloem fibers (Fig. 1)
The intrusive growth is performed by relatively few cells, which are surrounded by other cells that may grow symplastically, divide, or differentiate, making it very hard to obtain mRNA samples exclusively from the intrusively growing cells
Summary
The fiber intrusive elongation is very important for the development of plant architecture as well as for the yield and quality of commercial plant fibers[6,7,10]. To perform the RNA-Seq analysis for intrusively growing fibers, we have chosen primary phloem fibers of flax due to the well-characterized location within the stem and duration of the process[2]. The intrusive elongation is initiated at a 1–2-mm distance from the stem apex and continues several centimetres down the stem until the so-called “snap point”, where the transition of fibers to cell wall thickening occurs[13,14]. These morphological markers allow the study of stage-specific parameters of fiber development. Comparison of the obtained data with transcriptome landscapes in the tissues from the meristematic stem portions and in fibers at an advanced developmental stage enabled us (1) to characterize the overall picture of the transcriptome in the intrusively growing fibers, and (2) to determine which genes were subjected to up- and down-regulation of transcription at this critical stage of fiber development
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