Fischer Urs, Ikeda Yoshihisa, Ljung Karin, Serralbo Olivier, Singh Manoj, Heidstra Renze, Palme Klaus, Scheres Ben, Grebe Markus
Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, 90183 Umeå, Sweden.
Curr Biol. 2006 Nov 7;16(21):2143-9. doi: 10.1016/j.cub.2006.08.091.
Cell polarity is commonly coordinated within the plane of a single tissue layer (planar polarity), and hair positioning has been exploited as a simple marker for planar polarization of animal epithelia . The root epidermis of the plant Arabidopsis similarly reveals planar polarity of hair localization close to root tip-oriented (basal) ends of hair-forming cells . Hair position is directed toward a concentration maximum of the hormone auxin in the root tip , but mechanisms driving this plant-specific planar polarity remain elusive. Here, we report that combinatorial action of the auxin influx carrier AUX1, ETHYLENE-INSENSITIVE2 (EIN2) , and GNOM genes mediates the vector for coordinate hair positioning. In aux1;ein2;gnom eb triple mutant roots, hairs display axial (apical or basal) instead of coordinate polar (basal) position, and recruitment of Rho-of-Plant (ROP) GTPases to the hair initiation site reveals the same polar-to-axial switch. The auxin concentration gradient is virtually abolished in aux1;ein2;gnom eb roots, where locally applied auxin can coordinate hair positioning. Moreover, auxin overproduction in sectors of wild-type roots enhances planar ROP and hair polarity over long and short distances. Hence, auxin may provide vectorial information for planar polarity that requires combinatorial AUX1, EIN2, and GNOM activity upstream of ROP positioning.
细胞极性通常在单个组织层平面内协调（平面极性），毛发定位已被用作动物上皮细胞平面极化的一个简单标记。植物拟南芥的根表皮同样显示出毛发定位的平面极性，靠近毛发形成细胞的根尖导向（基部）末端。毛发位置指向根尖中激素生长素的浓度最大值，但驱动这种植物特有的平面极性的机制仍然难以捉摸。在这里，我们报告生长素流入载体AUX1、乙烯不敏感2（EIN2）和GNOM基因的组合作用介导了协调毛发定位的向量。在aux1;ein2;gnom eb三重突变体根中，毛发显示轴向（顶端或基部）而非协调的极性（基部）位置，并且植物Rho GTP酶（ROP）募集到毛发起始位点显示出相同的从极性到轴向的转变。在aux1;ein2;gnom eb根中生长素浓度梯度几乎消失，在这些根中局部施加生长素可以协调毛发定位。此外，野生型根的部分区域中生长素的过量产生在长距离和短距离上增强了平面ROP和毛发极性。因此，生长素可能为平面极性提供向量信息，这需要在ROP定位上游有AUX1、EIN2和GNOM的组合活性。
