Molecular genetic study on mechanisms of auxin action controlling growth of higher plants

本研究分离到一株拟南芥突变体msg1，该突变体单侧施加生长素诱导下胚轴的生长弯曲响应有缺陷。Msg1被发现是非光敏突变体nph4的等位基因（Liscum and Briggs, 1995）。Msg1下胚轴向地性、生长素诱导的生长弯曲性和向光性受损；它们对生长素有抵抗力。Msg1在形状上与野生型相似，除了上胚芽或下胚芽莲座叶。这些结果表明msg1在生长素特异性生长曲率响应中存在缺陷。我们检查了许多生长突变体的拟南芥生长素诱导的生长曲率响应。但是，我们发现只有axr1缺乏生长反应。Axr1的下胚轴向地性和光性均受损，表明Axr1是另一种生长素特异性生长曲率突变体。为了确定MSG1和AXR1在生长素依赖性生长曲率响应中的关系，我们在MSG1和AXR1之间构建了双muta…More nt，并测量了其生长曲率响应。msg1和axr1单突变体均部分丧失下胚轴的趋光性；Msg1 axr1双突变体对下胚轴无趋光性。两个单突变体的向重力性均受到部分影响；双突变体的下胚轴向地性缺陷大于单突变体。Axr1的莲座叶皱褶，msg1的莲座叶上紧；双突变体msg1 axr1叶片起皱，呈上胚层。这些结果表明，msg1和axr1突变的影响是加性的。换句话说，我们可以得出结论，MSG1和AXR1在生长素特异性生长曲率响应中独立作用。研究了吲哚-3-乙酸、2,4-二氯苯氧乙酸和1-萘乙酸对aux1根倾斜性异常的影响。发现只有添加萘乙酸才能恢复aux1的向重力性。这一发现以及对AUX1蛋白氨基酸序列的预测（Q3ennett et al., 1996）表明，UX1可能编码生长素内流载体。少

We isolated an Arabidopsis mutant, msg1, which was defective in growth curvature response of hypocotyl induced by unilateral application of auxin. Msg1 was found allelic to the nonphototropic mutant, nph4 (Liscum and Briggs, 1995). msg1 hypocotyls were impaired in gravitropism as well as the auxin-induced growth curvature and phototropism ; they were resistant to auxin. msg1 was similar to wild type in shape except for epinastic or hyponastic rosette leaves. These results indicate that msg1 is defective in auxin-specific growth curvature responses. We checked many growth mutants of Arabidopsis with respect to the auxin-induced growth curvature response. But, we found that only axr1 lacked the growth response. Axr1 hypocotyls were impaired in both gravitropism and phototropism, indicating that axr1 was another auxin-specific growth curvature mutant. in order to determine the relationship between MSG1 and AXR1 in the auxin-dependent growth curvature response, we constructed a double muta … More nt between msg1 and axr1, and measured its growth curvature responses. Both msg1 and axr1 single mutants lost phototropism of hypocotyl partially ; msg1 axr1 double mutants displayed no phototropism of hypocotyl. Gravitropism of both single mutants was affected partially ; defects in hypocotyl gravitropism of the double mutant were larger than those of either single mutant. Axr1 rosette leaves were wrinkled, while msg1 leaves were epinastic ; leaves of msg1 axr1 double mutant were wrinkled and epinastic. These results indicate that effects of mutations in msg1 and axr1 were additive. In other words, we can conclude that MSG1 and AXR1 act independently in auxin-specific growth curvature responses.We also investigated effects of indole-3-acetic acid, 2,4-dichhlorophenoxyacetic acid and 1-naphthaleneacetic acid on abberant gravitropism of aux1 roots. It was found that only an addition of naphthaleneacetic acid restored aux1 gravitropism. This finding as well as the predicted amino acid sequence of AUX1 protein Q3ennett et al., 1996) indicates that A UX1 probably encodes an auxin influx carrier. Less