Transcriptional Profiling of Mature Arabidopsis Trichomes Reveals That NOECK Encodes the MIXTA-Like Transcriptional Regulator MYB106    

Abstract

Leaf hairs (trichomes) of Arabidopsis (Arabidopsis thaliana) have been extensively used as a model to address general questions in cell and developmental biology. Here, we lay the foundation for a systems-level understanding of the biology of this model cell type by performing genome-wide gene expression analyses. We have identified 3,231 genes that are up-regulated in mature trichomes relative to leaves without trichomes, and we compared wild-type trichomes with two mutants, glabra3 and triptychon, that affect trichome morphology and physiology in contrasting ways. We found that cell wall-related transcripts were particularly overrepresented in trichomes, consistent with their highly elaborated structure. In addition, trichome expression maps revealed high activities of anthocyanin, flavonoid, and glucosinolate pathways, indicative of the roles of trichomes in the biosynthesis of secondary compounds and defense. Interspecies comparisons revealed that Arabidopsis trichomes share many expressed genes with cotton (Gossypium hirsutum) fibers, making them an attractive model to study industrially important fibers. In addition to identifying physiological processes involved in the development of a specific cell type, we also demonstrated the utility of transcript profiling for identifying and analyzing regulatory gene function. One of the genes that are differentially expressed in fibers is the MYB transcription factor GhMYB25. A combination of transcript profiling and map-based cloning revealed that the NOECK gene of Arabidopsis encodes AtMYB106, a MIXTA-like transcription factor and homolog of cotton GhMYB25. However, in contrast to Antirrhinum, in which MIXTA promotes epidermal cell outgrowth, AtMYB106 appears to function as a repressor of cell outgrowth in Arabidopsis.

Lack of α-Xylosidase Activity in Arabidopsis Alters Xyloglucan Composition and Results in Growth Defects

“…The ubiquity of reporter expression under the control of the AtXYL1 promoter at the organ level is also reflected in published genome-wide microarray analyses (Schmid et al, 2005;Jakoby et al, 2008). Cell type-specific studies confirm the expression of AtXYL1 in guard cells and trichomes as well as a lack of expression in pollen (Pina et al, 2005;Jakoby et al, 2008;Yang et al, 2008). The expression pattern revealed by the promoter-reporter fusion is remarkably similar to that of MUR3, a galactosyltransferase involved in xyloglucan synthesis (Madson et al, 2003).…”

“…5), appears to be widespread, as would be expected for the only a-xylosidase active against xyloglucan. The ubiquity of reporter expression under the control of the AtXYL1 promoter at the organ level is also reflected in published genome-wide microarray analyses (Schmid et al, 2005;Jakoby et al, 2008). Cell type-specific studies confirm the expression of AtXYL1 in guard cells and trichomes as well as a lack of expression in pollen (Pina et al, 2005;Jakoby et al, 2008;Yang et al, 2008).…”

CULLIN 4-RING FINGER-LIGASE plays a key role in the control of endoreplication cycles in Arabidopsis trichomes

“…5 and SI Methods). In our model, a mitotic cycle is converted into an endocycle through a developmentally controlled (trichome specification) wave of the presumptive CDK inhibitor SIM, completely blocking M-phase CDK activity during further trichome development; this takes into account that SIM is a direct target of the trichome specification machinery and one of the highest expressed genes in trichomes (45,46). It should be noted that moderate levels of SIM or related inhibitors might also be used in plants to delay the M-phase CDK activity and, by that, to establish a G2 phase (44).…”

AtTIP1;3 and AtTIP5;1, the only highly expressed Arabidopsis pollen‐specific aquaporins, transport water and urea

“…1a) [17]. We also performed a comparative analysis of aquaporin expression between mature pollen (MP) [7] and single cell types such as trichome cells (TC) [18], mesophyll cells (MC) [19], stomatal guard cells (GC) [19] and lateral root cap stage I (LRC) used as a representative of the transcriptomic analysis obtained for three developmental stages in five different domains of Arabidopsis root [20]. We found that trichome cells (TC), mesophyll cells (MC), stomatal guard cells (GC) and lateral root cap cells stage 1 (LRC), or any other root cell type (data not shown), all expressed a larger number of aquaporin genes (13, 13, 14 and 17, respectively) compared to Arabidopsis mature pollen grains that only expressed 6 (Fig.…”