Intensity of a pulse of RSL4 transcription factor synthesis determines Arabidopsis root hair cell size

Abstract

Cell size is determined by the duration and rate of growth and plays a central role in cell function. Root hairs are tip-growing cellular projections that emerge from the root epidermis and explore the soil to acquire nutrients and water(1). Previously we demonstrated that the basic helix-loop-helix transcription factor root hair defective 6-like 4 (RSL4) is necessary and sufficient for root hair growth(2). Here we show that RSL4 is synthesized in a 4-h pulse at the initiation of hair elongation and is gradually degraded by the 26S proteasome. The amount of RSL4 synthesis during this pulse is modulated as part of a root hair growth response to low phosphate. RSL4 synthesis increases in low phosphate and this increase prolongs the growth phase, resulting in the development of long root hairs. Our data demonstrate that the amount of RSL4 synthesized during the pulse directly determines the final size of the differentiated root hair cell. We propose that the modulation of growth-promoting transcription factors by external cues could be a general mechanism for the regulation of cell growth by environmental factors during development.

Dioxygenase-encoding AtDAO1 gene controls IAA oxidation and homeostasis in Arabidopsis

“…RH determination and elongation in Arabidopsis is controlled (in part) by a small family of basic HelixLoop-Helix transcription factors that includes the auxin-inducible gene member RSL4 (14-16). Datta et al (17) have recently shown that RH length is proportional to RSL4 mRNA abundance. Significantly, qRT-PCR analysis revealed that dao1-1 and dao1-3 seedlings contained an ∼80% increase in RSL4 transcript levels (Fig.…”

The regulation and plasticity of root hair patterning and morphogenesis

“…RSL4 is a direct target of ROOT HAIR DEFECTIVE 6 (RHD6), a VIIIc subfamily bHLH transcription factor that promotes the early stages of root hair development, and is suggested to represent the conversion point of internal and environmental cues (Masucci and Schiefelbein, 1996). RSL4 is expressed in Arabidopsis trichoblasts in the elongation zone immediately prior to initiation of root-hair outgrowth, and it controls a suite of genes encoding proteins that are required for root hair morphogenesis (Yi et al, 2010;Datta et al, 2015). Of note, RSL4 is rapidly degraded after root hair elongation is initiated; Pi deficiency significantly increases the synthesis and half-life of RSL4 (Datta et al, 2015).…”

“…Pi deficiency-induced prolonged growth of root hairs is directly correlated with the intensity of a translational pulse of the bHLH transcription factor ROOT HAIR DEFECTIVE 6-LIKE 4 (RSL4) (Yi et al, 2010;Datta et al, 2015). RSL4 is a direct target of ROOT HAIR DEFECTIVE 6 (RHD6), a VIIIc subfamily bHLH transcription factor that promotes the early stages of root hair development, and is suggested to represent the conversion point of internal and environmental cues (Masucci and Schiefelbein, 1996).…”

“…RSL4 is expressed in Arabidopsis trichoblasts in the elongation zone immediately prior to initiation of root-hair outgrowth, and it controls a suite of genes encoding proteins that are required for root hair morphogenesis (Yi et al, 2010;Datta et al, 2015). Of note, RSL4 is rapidly degraded after root hair elongation is initiated; Pi deficiency significantly increases the synthesis and half-life of RSL4 (Datta et al, 2015). The function of RSL4 appears to be conserved; natural and synthetic allopolyploid wheat form longer root hairs than their diploid progenitors, a trait that was positively correlated with the expression level of TaRSL4 (Han et al, 2016).…”

Increased root hair density by loss of WRKY6 in Arabidopsis thaliana

“…The length is critically dependent on the activity of the transcription factor ROOT HAIR DEFECTIVE 6-LIKE 4 (RSL4), which is necessary and sufficient for root hair growth (Datta et al, 2015). The elongation time and the growth rates are promoted under Pi deficiency, leading to longer root hairs in the Arabidopsis accession Col-0 (Bates and Lynch, 1996).…”