Schneider K, Mathur J, Boudonck K, Wells B, Dolan L, Roberts K
Department of Cell Biology, John Innes Centre, Colney, Norwich, NR4 7UH, UK.
Genes Dev. 1998 Jul 1;12(13):2013-21. doi: 10.1101/gad.12.13.2013.
The epidermis of Arabidopsis wild-type primary roots, in which some cells grow hairs and others remain hairless in a position-dependent manner, has become an established model system to study cell differentiation. Here we present a molecular analysis of the RHL1 (ROOT HAIRLESS 1) gene that, if mutated, prevents the formation of hairs on primary roots and causes a seedling lethal phenotype. We have cloned the RHL1 gene by use of a T-DNA-tagged mutant and found that it encodes a protein that appears to be plant specific. The predicted RHL1 gene product is a small hydrophilic protein (38.9 kD) containing putative nuclear localization signals and shows no significant homology to any known amino acid sequence. We demonstrate that a 78-amino-acid sequence at its amino terminus is capable of directing an RHL1-GFP fusion protein to the nucleus. The RHL1 transcript is present throughout the wild-type plant and in suspension culture cells, but in very low amounts, suggesting a regulatory function for the RHL1 protein. Structural evidence suggests a role for the RHL1 gene product in the nucleolus. We have examined the genetic relationship between RHL1 and GL2, an inhibitor of root hair initiation in non-hair cells. Our molecular and genetic data with double mutants, together with the expression analysis of a GL2 promoter-GUS reporter gene construct, indicate that the RHL1 gene acts independently of GL2.
拟南芥野生型初生根的表皮中，一些细胞以位置依赖的方式长出根毛，而另一些细胞则不长根毛，这已成为研究细胞分化的成熟模型系统。在此，我们对RHL1（根无毛1）基因进行了分子分析，该基因若发生突变，会阻止初生根上根毛的形成，并导致幼苗致死表型。我们利用一个T-DNA标签突变体克隆了RHL1基因，发现它编码一种似乎是植物特有的蛋白质。预测的RHL1基因产物是一种小的亲水性蛋白质（38.9 kD），含有假定的核定位信号，且与任何已知氨基酸序列均无显著同源性。我们证明其氨基末端的一个78个氨基酸的序列能够将RHL1-GFP融合蛋白导向细胞核。RHL1转录本存在于整个野生型植株和悬浮培养细胞中，但含量极低，这表明RHL1蛋白具有调节功能。结构证据表明RHL1基因产物在核仁中发挥作用。我们研究了RHL1与GL2之间的遗传关系，GL2是无毛细胞中根毛起始的抑制剂。我们对双突变体的分子和遗传数据，以及GL2启动子-GUS报告基因构建体的表达分析表明，RHL1基因独立于GL2发挥作用。
