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Abstract Root hairs are single-cell protrusions that enable roots to optimize nutrient and water acquisition. These structures attain their tubular shapes by confining growth to the cell apex, a process called tip growth. The actin cytoskeleton and endomembrane systems are essential for tip growth; however, little is known about how these cellular components coordinate their activities during this process. Here, we show that SPIRRIG (SPI), a beige and Chediak Higashi domain-containing protein involved in membrane trafficking, and BRK1 and SCAR2, subunits of the WAVE/SCAR (W/SC) actin nucleating promoting complex, display polarized localizations in Arabidopsis thaliana root hairs during distinct developmental stages. SPI accumulates at the root hair apex via post-Golgi compartments and positively regulates tip growth by maintaining tip-focused vesicle secretion and filamentous-actin integrity. BRK1 and SCAR2 on the other hand, mark the root hair initiation domain to specify the position of root hair emergence. Consistent with the localization data, tip growth was reduced in spi and the position of root hair emergence was disrupted in brk1 and scar1234. BRK1 depletion coincided with SPI accumulation as root hairs transitioned from initiation to tip growth. Taken together, our work uncovers a role for SPI in facilitating actin-dependent root hair development in Arabidopsis through pathways that might intersect with W/SC.
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This content will become publicly available on December 1, 2025
SPIRRIG is required for BRICK1 stability and salt stress induced root hair developmental plasticity in Arabidopsis
Developmental plasticity is critical for plants to adapt to constantly changing environments. Plant root hairs display dramatic plasticity under different environments and therefore play crucial roles in defense against environmental stressors. Here, we report the isolation of an Arabidopsis mutant, salinity over-sensitive mutant 1-1 (som1-1), also exhibiting root hair developmental defects. Map-based cloning and allelic analyses confirmed that som1-1 is a new mutant allele of SPIRRIG (SPI), which encodes a Beige and Chediak Higashi (BEACH) domain-containing protein. SPI has been reported to facilitate actin dependent root hair development by temporally and spatially regulating the expression of BRICK1 (BRK1), a subunit of the SCAR/WAVE actin nucleating promoting complex. Our living cell imaging examinations revealed that salt stress induces an altered actin organization in root hair that mimics those in the spi mutant, implying SPI may respond to salt stress induced root hair plasticity by modulating actin cytoskeleton organization. Furthermore, we found BRK1 is also involved in root hair developmental change under salt stress, and overexpression of BRK1 resulted in root hairs over-sensitive to salt stress as those in spi mutant. Moreover, based on biochemical analyses, we found BRK1 is unstable and SPI mediates BRK1 stability. Functional loss of SPI results in the accumulation of steady-state of BRK1.
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- Award ID(s):
- 2425989
- PAR ID:
- 10640511
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- Stress Biology
- Volume:
- 4
- Issue:
- 1
- ISSN:
- 2731-0450
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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