Hobbie L, Estelle M
Department of Biology, Indiana University, Bloomington 47405.
Plant J. 1995 Feb;7(2):211-20. doi: 10.1046/j.1365-313x.1995.7020211.x.
To understand the molecular mechanism of auxin action, mutants of Arabidopsis thaliana with altered responses to auxin have been identified and characterized. Here the isolation of two auxin-resistant mutants that define a new locus involved in auxin response, named AXR4, is reported. The axr4 mutations are recessive and map near the ch1 mutation on chromosome 1. Mutant plants are specifically resistant to auxin and defective in root gravitropism. Double mutants between axr4 and the recessive auxin-resistant mutants axr1-3 and aux1-7 were characterized to ascertain possible genetic interactions between the mutations. The roots of the axr4 axr1-3 double mutant plants are less sensitive to auxin, respond more slowly to gravity, and form fewer lateral roots than either parental single mutant. These results suggest that the two mutations have additive or even synergistic effects. The AXR1 and AXR4 gene products may therefore act in separate pathways of auxin response or perhaps perform partially redundant functions in a single pathway. The axr4 aux1-7 double mutant has the same sensitivity to auxin as the aux1-7 mutant but forms far fewer lateral roots than either parental single mutant. The aux1-7 mutation thus appears to be epistatic to axr4 with respect to auxin-resistant root elongation, whereas in lateral root formation, the effects of the two mutations are additive. The complexity of the genetic interactions indicated by these results may reflect differences in the mechanism of auxin action during root elongation and the formation of lateral roots. The AXR4 gene product, along with those of the AXR1 and AUX1 genes, is important for normal auxin sensitivity, gravitropic response in roots and lateral root formation.
为了解生长素作用的分子机制，已鉴定并表征了拟南芥中对生长素反应改变的突变体。本文报道了两个生长素抗性突变体的分离，它们定义了一个参与生长素反应的新位点，命名为AXR4。axr4突变是隐性的，位于1号染色体上ch1突变附近。突变植株对生长素具有特异性抗性，且根向地性存在缺陷。对axr4与隐性生长素抗性突变体axr1 - 3和aux1 - 7之间的双突变体进行了表征，以确定突变之间可能的遗传相互作用。axr4 axr1 - 3双突变体植株的根对生长素的敏感性较低，对重力的反应较慢，并且形成的侧根比任何一个亲本单突变体都少。这些结果表明这两个突变具有累加甚至协同效应。因此，AXR1和AXR4基因产物可能在生长素反应的不同途径中起作用，或者在单一途径中执行部分冗余功能。axr4 aux1 - 7双突变体对生长素的敏感性与aux1 - 7突变体相同，但形成的侧根比任何一个亲本单突变体都少得多。因此，就生长素抗性根伸长而言，aux1 - 7突变似乎对axr4是上位性的，而在侧根形成方面，两个突变的效应是累加的。这些结果表明的遗传相互作用的复杂性可能反映了根伸长和侧根形成过程中生长素作用机制的差异。AXR4基因产物与AXR1和AUX1基因的产物一起，对于正常的生长素敏感性、根的向地性反应和侧根形成都很重要。
