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Spatial and temporal localization of SPIRRIG and WAVE/SCAR reveal roles for these proteins in actin-mediated root hair development.

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.

SUBMITTER: Chin S

PROVIDER: S-EPMC8364238 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Actin polymerization drives polar growth in Arabidopsis root hair cells.

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Project description:The Scar/WAVE regulatory complex (WRC) is the main catalyst of pseudopod and lamellipodium formation during cell migration. Its actin nucleation activity has been attributed to its ability to activate the Arp2/3 complex through the VCA domain of Scar/WAVE. Here we show in both B16-F1 mouse melanoma cells and Dictyostelium discoideum cells that the WRC with its VCA domain deleted can still induce the formation of morphologically normal actin protrusions. Its function is lost only after further deletion of Scar/WAVE’s (in Dictyostelium cells) or both Abi and WAVE’s (in B16-F1 cells) proline-rich domains. Moreover, mass spectrometry analysis identified BAIAP2 and Vasp (both promotors of actin polymerization) as specific interactors of WRC polyproline domains. Thus we conclude that proline-rich domains play a central role in actin nucleation by concentrating other effectors needed to form actin protrusions. Together, these findings suggest a new mechanism for WRC action independent of the VCA-Arp2/3 interaction.

2024-08-30 | PXD037123 | Pride

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