AUTHOR=Zhang Hui-Ming , Wheeler Simon L. , Xia Xue , Colyvas Kim , Offler Christina E. , Patrick John W. 

TITLE=Transcript Profiling Identifies Gene Cohorts Controlled by Each Signal Regulating Trans-Differentiation of Epidermal Cells of Vicia faba Cotyledons to a Transfer Cell Phenotype

JOURNAL=Frontiers in Plant Science

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.02021

DOI=10.3389/fpls.2017.02021

ISSN=1664-462X

ABSTRACT=<p>Transfer cells (TCs) support high rates of membrane transport of nutrients conferred by a plasma membrane area amplified by lining a wall labyrinth comprised of an uniform wall layer (UWL) upon which intricate wall ingrowth (WI) papillae are deposited. A signal cascade of auxin, ethylene, extracellular hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) and cytosolic Ca<sup>2+</sup> regulates wall labyrinth assembly. To identify gene cohorts regulated by each signal, a RNA- sequencing study was undertaken using <italic>Vicia faba</italic> cotyledons. When cotyledons are placed in culture, their adaxial epidermal cells spontaneously undergo <italic>trans</italic>-differentiation to epidermal TCs (ETCs). Expressed genes encoding proteins central to wall labyrinth formation (signaling, intracellular organization, cell wall) and TC function of nutrient transport were assembled. Transcriptional profiles identified 9,742 annotated ETC-specific differentially expressed genes (DEGs; Log<sub>2</sub>fold change &gt; 1; FDR p ≤ 0.05) of which 1,371 belonged to signaling (50%), intracellular organization (27%), cell wall (15%) and nutrient transporters (9%) functional categories. Expression levels of 941 ETC-specific DEGs were found to be sensitive to the known signals regulating ETC <italic>trans</italic>-differentiation. Significantly, signals acting alone, or in various combinations, impacted similar numbers of ETC-specific DEGs across the four functional gene categories. Amongst the signals acting alone, H<sub>2</sub>O<sub>2</sub> exerted most influence affecting expression levels of 56% of the ETC-specific DEGs followed by Ca<sup>2+</sup> (21%), auxin (18%) and ethylene (5%). The dominance by H<sub>2</sub>O<sub>2</sub> was evident across all functional categories, but became more attenuated once <italic>trans</italic>-differentiation transitioned into WI papillae formation. Amongst the eleven signal combinations, H<sub>2</sub>O<sub>2</sub>/Ca<sup>2+</sup> elicited the greatest impact across all functional categories accounting for 20% of the ETC-specific DEG cohort. The relative influence of the other signals acting alone, or in various combinations, varied across the four functional categories and two phases of wall labyrinth construction. These transcriptome data provide a powerful information platform from which to examine signal transduction pathways and how these regulate expression of genes encoding proteins engaged in intracellular organization, cell wall construction and nutrient transport.</p>