Fridborg I, Kuusk S, Robertson M, Sundberg E
Department of Physiological Botany, Evolutionary Biology Centre, Uppsala University, Villavägen 6, S-752 36 Uppsala, Sweden.
Plant Physiol. 2001 Nov;127(3):937-48.
The current model of gibberellin (GA) signal transduction is based on a derepressible system and a number of candidate negative regulators have been identified in Arabidopsis. We previously have reported the identification of the Arabidopsis gene SHORT INTERNODES (SHI) that causes suppression of GA responses when constitutively activated. In this paper, we show by using reporter gene analysis that the SHI gene is expressed in young organs, e.g. shoot apices and root tips. The model predicts a suppressor of GA responses to be active in these tissues to prevent premature growth or development. To study the effect of SHI on GA signaling, we used a functional assay that measures effects of signaling components on a well-defined GA response; the up-regulation of alpha-amylase in barley (Hordeum vulgare) aleurones in response to GA treatment. We found that SHI was able to specifically block the activity of a high-isoelectric point alpha-amylase promoter following GA(3) treatment, which further supports that SHI is a suppressor of GA responses. We have identified two putative loss-of-function insertion alleles of SHI and lines homozygous for either of the new alleles show no phenotypic deviations from wild type. Because SHI belongs to a gene family consisting of nine members, we suggest that SHI and the SHI-related genes are functionally redundant. We also show that a functional ERECTA allele is able to partly suppress the dwarfing effect of the shi gain-of-function mutation, suggesting that the erecta mutation harbored by the Landsberg erecta ecotype is an enhancer of the shi dwarf phenotype.
目前赤霉素（GA）信号转导模型基于一个可解除抑制的系统，并且在拟南芥中已鉴定出许多候选负调控因子。我们之前报道了拟南芥SHORT INTERNODES（SHI）基因的鉴定，该基因在组成型激活时会导致GA反应受到抑制。在本文中，我们通过报告基因分析表明，SHI基因在幼嫩器官如茎尖和根尖中表达。该模型预测GA反应的一个抑制因子在这些组织中起作用以防止过早生长或发育。为了研究SHI对GA信号传导的影响，我们使用了一种功能分析方法，该方法可测量信号成分对明确的GA反应的影响；即大麦（Hordeum vulgare）糊粉层中α-淀粉酶响应GA处理的上调。我们发现，GA(3)处理后，SHI能够特异性阻断高异电点α-淀粉酶启动子的活性，这进一步支持SHI是GA反应的一个抑制因子。我们鉴定出SHI的两个推定的功能缺失插入等位基因，并且对于这两个新等位基因中的任何一个纯合的株系与野生型相比均未表现出表型偏差。因为SHI属于一个由九个成员组成的基因家族，我们认为SHI和与SHI相关的基因在功能上是冗余的。我们还表明，一个功能性的ERECTA等位基因能够部分抑制shi功能获得型突变的矮化效应，这表明Landsberg erecta生态型中携带的erecta突变是shi矮化表型的一个增强子。
