Auxin and ROP GTPase signaling of polar nuclear migration in root epidermal hair cells
Plant Physiol. 2018,176(1):378-391
Nakamura M, Claes AR, Grebe T, Hermkes R, Viotti C, Ikeda Y, Grebe M

Abstract
Polar nuclear migration is crucial during development of diverse eukaryotes. In plants, root hair growth requires polar nuclear migration into the outgrowing hair. However, knowledge about the dynamics and the regulatory mechanisms underlying nuclear movements in root epidermal cells remains limited. Here, we show that both auxin and Rho-of-Plant (ROP) signaling modulate polar nuclear position at the inner epidermal plasma membrane domain oriented to the cortical cells during cell elongation as well as subsequent polar nuclear movement to the outer domain into the emerging hair bulge in Arabidopsis thaliana. Auxin signaling via the nuclear AUXIN RESPONSE FACTOR7 (ARF7)/ARF19 and IAA7 pathway ensures correct nuclear placement towards the inner membrane domain. Moreover, precise inner nuclear placement relies on SPIKE1 Rho-GEF, SUPERCENTIPEDE1 Rho-GDI and ACTIN7 (ACT7) function as well as to a lesser extent on VTI11 vacuolar SNARE activity. Strikingly, directionality and/or velocity of outer polar nuclear migration into the hair outgrowth along actin strands are also ACT7-dependent, auxin-sensitive and regulated by ROP signaling. Thus, our findings provide a founding framework revealing auxin and ROP signaling of inner polar nuclear position with some contribution by vacuolar morphology and of actin-dependent outer polar nuclear migration in root epidermal hair cells.

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