Rampey Rebekah A, Woodward Andrew W, Hobbs Brianne N, Tierney Megan P, Lahner Brett, Salt David E, Bartel Bonnie
Department of Biology, Harding University, Searcy, AR 72149, USA.
Genetics. 2006 Dec;174(4):1841-57. doi: 10.1534/genetics.106.061044. Epub 2006 Oct 8.
The plant hormone auxin can be regulated by formation and hydrolysis of amide-linked indole-3-acetic acid (IAA) conjugates. Here, we report the characterization of the dominant Arabidopsis iaa-leucine resistant3 (ilr3-1) mutant, which has reduced sensitivity to IAA-Leu and IAA-Phe, while retaining wild-type responses to free IAA. The gene defective in ilr3-1 encodes a basic helix-loop-helix leucine zipper protein, bHLH105, and the ilr3-1 lesion results in a truncated product. Overexpressing ilr3-1 in wild-type plants recapitulates certain ilr3-1 mutant phenotypes. In contrast, the loss-of-function ilr3-2 allele has increased IAA-Leu sensitivity compared to wild type, indicating that the ilr3-1 allele confers a gain of function. Microarray and quantitative real-time PCR analyses revealed five downregulated genes in ilr3-1, including three encoding putative membrane proteins similar to the yeast iron and manganese transporter Ccc1p. Transcript changes are accompanied by reciprocally misregulated metal accumulation in ilr3-1 and ilr3-2 mutants. Further, ilr3-1 seedlings are less sensitive than wild type to manganese, and auxin conjugate response phenotypes are dependent on exogenous metal concentration in ilr3 mutants. These data suggest a model in which the ILR3/bHLH105 transcription factor regulates expression of metal transporter genes, perhaps indirectly modulating IAA-conjugate hydrolysis by controlling the availability of metals previously shown to influence IAA-amino acid hydrolase protein activity.
植物激素生长素可通过酰胺连接的吲哚 - 3 - 乙酸（IAA）共轭物的形成和水解来调节。在此，我们报道了拟南芥主要的iaa - 亮氨酸抗性3（ilr3 - 1）突变体的特征，该突变体对IAA - 亮氨酸和IAA - 苯丙氨酸的敏感性降低，同时对游离IAA保持野生型反应。ilr3 - 1中缺陷的基因编码一种碱性螺旋 - 环 - 螺旋亮氨酸拉链蛋白bHLH105，并且ilr3 - 1损伤导致截短产物。在野生型植物中过表达ilr3 - 1重现了某些ilr3 - 1突变体表型。相比之下，功能缺失的ilr3 - 2等位基因与野生型相比对IAA - 亮氨酸的敏感性增加，表明ilr3 - 1等位基因赋予了功能获得。微阵列和定量实时PCR分析揭示了ilr3 - 1中有五个下调基因，包括三个编码与酵母铁和锰转运蛋白Ccc1p相似的推定膜蛋白的基因。转录变化伴随着ilr3 - 1和ilr3 - 2突变体中金属积累的相互失调。此外，ilr3 - 1幼苗对锰的敏感性低于野生型，并且生长素共轭物反应表型取决于ilr3突变体中的外源金属浓度。这些数据提出了一个模型，其中ILR3 / bHLH105转录因子调节金属转运蛋白基因的表达，可能通过控制先前显示影响IAA - 氨基酸水解酶蛋白活性的金属的可用性来间接调节IAA - 共轭物水解。
