Cell Biology & Molecular Genetics

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    Transcriptional profiling of Arabidopsis root hairs and pollen defines an apical cell growth signature
    (Springer Nature, 2014-08-01) Becker, Jörg D; Takeda, Seiji; Borges, Filipe; Dolan, Liam; Feijó, José A
    Current views on the control of cell development are anchored on the notion that phenotypes are defined by networks of transcriptional activity. The large amounts of information brought about by transcriptomics should allow the definition of these networks through the analysis of cell-specific transcriptional signatures. Here we test this principle by applying an analogue to comparative anatomy at the cellular level, searching for conserved transcriptional signatures, or conserved small gene-regulatory networks (GRNs) on root hairs (RH) and pollen tubes (PT), two filamentous apical growing cells that are a striking example of conservation of structure and function in plants. We developed a new method for isolation of growing and mature root hair cells, analysed their transcriptome by microarray analysis, and further compared it with pollen and other single cell transcriptomics data. Principal component analysis shows a statistical relation between the datasets of RHs and PTs which is suggestive of a common transcriptional profile pattern for the apical growing cells in a plant, with overlapping profiles and clear similarities at the level of small GTPases, vesicle-mediated transport and various specific metabolic responses. Furthermore, cis-regulatory element analysis of co-regulated genes between RHs and PTs revealed conserved binding sequences that are likely required for the expression of genes comprising the apical signature. This included a significant occurrence of motifs associated to a defined transcriptional response upon anaerobiosis. Our results suggest that maintaining apical growth mechanisms synchronized with energy yielding might require a combinatorial network of transcriptional regulation. We propose that this study should constitute the foundation for further genetic and physiological dissection of the mechanisms underlying apical growth of plant cells.
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    POLLEN TUBES FAIL TO TARGET OVULE IN THE ABSENCE OF TWO CATION/PROTON EXCHANGERS IN ARABIDOPSIS
    (2010) Lu, Yongxian; Sze, Heven; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Flowering plant reproduction requires precise delivery of the sperm cells to the ovule by a pollen tube. Guiding signals from female cells are being identified, though how pollen senses and responds to those cues are largely unknown. Here I provide genetic evidence that two predicted cation/proton exchangers expressed in Arabidopsis pollen play essential roles in pollen targeting of ovules. Male fertility was unchanged in single chx21 or chx23 mutant pollen; however, male-specific gene transmission was blocked in chx21chx23 double mutant. Wild-type pistil provided with a limited amount of pollen containing a mixture of single and double mutant produced ~60% less seeds compared to that produced with chx23 single mutant pollen, indicating that chx21chx23 pollen is infertile. The double mutant pollen, visualized by a pollen-specific promoter-driven GUS activity, germinated and extended a tube down the transmitting tract, but the tube failed to turn and target an ovule. Unlike wild-type pollen that targeted isolated ovules in a semi-in vivo assay, tube guidance in chx21chx23 pollen was compromised. As a first step to understand the cellular and molecular bases of tube guidance, membrane localization and activity of CHX23 was determined. GFP-tagged CHX23 was localized to endomembranes, predominantly endoplasmic reticulum (ER), in elongating pollen tubes. Furthermore, expression of CHX23 in E. coli resulted in enhanced K+ accumulation at alkaline pH, suggesting a role for CHX23 in K+ acquisition and pH homeostasis. Based on these studies and observations by others that ER oscillates and enters the apex, a simple model is proposed: Modification of localized pH by CHX21 or CHX23 enables pollen tube to sense female signals and respond by shifting directional growth at the funiculus and micropyle to target pollen tip growth towards the ovule.