The Auxin-Regulated CrRLK1L Kinase ERULUS Controls Cell Wall Composition during Root Hair Tip Growth

Abstract

Root hairs facilitate a plant's ability to acquire soil anchorage and nutrients. Root hair growth is regulated by the plant hormone auxin and dependent on localized synthesis, secretion, and modification of the root hair tip cell wall. However, the exact cell wall regulators in root hairs controlled by auxin have yet to be determined. In this study, we describe the characterization of ERULUS (ERU), an auxin-induced Arabidopsis receptor-like kinase, whose expression is directly regulated by ARF7 and ARF19 transcription factors. ERU belongs to the Catharanthus roseus RECEPTOR-LIKE KINASE 1-LIKE (CrRLK1L) subfamily of putative cell wall sensor proteins. Imaging of a fluorescent fusion protein revealed that ERU is localized to the apical root hair plasma membrane. ERU regulates cell wall composition in root hairs and modulates pectin dynamics through negative control of pectin methylesterase (PME) activity. Mutant eru (-/-) root hairs accumulate de-esterified homogalacturonan and exhibit aberrant pectin Ca-binding site oscillations and increased PME activity. Up to 80% of the eru root hair phenotype is rescued by pharmacological supplementation with a PME-inhibiting catechin extract. ERU transcription is altered in specific cell wall-related root hair mutants, suggesting that it is a target for feedback regulation. Loss of ERU alters the phosphorylation status of FERONIA and H-ATPases 1/2, regulators of apoplastic pH. Furthermore, H-ATPases 1/2 and ERU are differentially phosphorylated in response to auxin. We conclude that ERULUS is a key auxin-controlled regulator of cell wall composition and pectin dynamics during root hair tip growth.

Plant Trans-Golgi Network/Early Endosome pH regulation requires Cation Chloride Cotransporter (CCC1)

“…This revealed that Atccc1 root hairs were shorter because they grow at a reduced speed. The elongation rate of wildtype plants in our conditions was similar to what had previously been observed (Schoenaers et al, 2018). For wildtype, the average rate of root hair elongation between 50 and 100 minutes after elongation initiated was 0.88 ± 0.27 µm min 1- while Atccc1 root hairs elongated at half that speed, at 0.47 ± 0.08 µm min 1- , but for the same period of time, resulting in shorter root hairs (Fig.…”

Deep Sequencing Reveals Early Reprogramming of Arabidopsis Root Transcriptomes Upon Ralstonia solanacearum Infection

“…7A). The ERU, EXP7, and LRX1 genes, involved in root-hair elongation (Baumberger et al 2001;Lin et al 2011;Schoenaers et al 2018), were also quickly turned on at the NS stage (6 to 12 hpi) and were inactivated at the PC stage ( Fig. 7A).…”

Receptor‐like protein kinases: Key regulators controlling root hair development in Arabidopsis thaliana

“…Two most recent studies, appearing after this review article was accepted for publication, suggest that CAP1, also known as ERULUS (ERU), is actually localized on the plasma membrane instead of at the tonoplast (Kwon et al 2018;Schoenaers et al 2018). Kwon et al showed that CAP1/ERU maintains tip-focused cytoplasmic calcium oscillations in root hairs via an unknown mechanism (Kwon et al 2018).…”

“…Kwon et al showed that CAP1/ERU maintains tip-focused cytoplasmic calcium oscillations in root hairs via an unknown mechanism (Kwon et al 2018). Schoenaers et al demonstrated that CAP1/ERU is regulated by auxin and functions as an important regulator of cell wall composition during root hair tip growth (Schoenaers et al 2018).…”