Huang Danqiong, Dai Wenhao
Department of Plant Sciences, North Dakota State University, Fargo, ND, USA.
Plant Cell Rep. 2015 Jul;34(7):1211-24. doi: 10.1007/s00299-015-1779-8. Epub 2015 Feb 27.
Two Populus bHLH genes ( PtFIT and PtIRO ) were cloned and characterized. The iron deficiency tolerance may be regulated by the PtFIT -dependent response pathway in Populus. Five orthologs of eight Arabidopsis basic helix-loop-helix (bHLH) genes responding to iron deficiency in Populus were analyzed. Open reading frame (ORF) regions of two bHLH genes (PtFIT and PtIRO) were isolated from the iron deficiency tolerant (PtG) and susceptible (PtY) genotypes of Populus tremula 'Erecta'. Gene sequence analyses showed that each of the two genes was identical in PtG and PtY. Phylogenetic analysis revealed that PtFIT was clustered with the bHLH genes regulating iron deficiency responses, while PtIRO was clustered with another group of the bHLH genes regulating iron deficiency responses in a FIT-independent pathway. Tissue-specific expression analysis indicated that PtFIT was only detected in the root among all tested tissues, while PtIRO was rarely detected in all tested tissues. Real-time PCR showed that PtFIT was up-regulated in roots under the iron-deficient condition. A higher level of PtFIT transcripts was detected in PtG than in PtY. Pearson Correlation Coefficient calculations indicated a strong positive correlation (r = 0.94) between PtFIT and PtIRT1 in PtG. It suggests that the iron deficiency tolerance of PtG may be regulated by the PtFIT-dependent response pathway. The PtFIT-transgenic poplar plants had an increased expression level of PtFIT and PtIRT1 responding to iron deficiency. One PtFIT-transgenic line (TL2) showed enhanced iron deficiency tolerance with higher chlorophyll content and Chl a/b ratio under iron deficiency than the control plants, indicating that PtFIT is involved in iron deficiency response in Populus. The results would provide useful information to understand iron deficiency response mechanisms in woody species.
克隆并鉴定了两个胡杨bHLH基因（PtFIT和PtIRO）。胡杨对缺铁的耐受性可能受PtFIT依赖的反应途径调控。分析了杨树中8个拟南芥响应缺铁的基本螺旋-环-螺旋（bHLH）基因的5个直系同源基因。从欧洲山杨‘Erecta’的耐缺铁（PtG）和缺铁敏感（PtY）基因型中分离出两个bHLH基因（PtFIT和PtIRO）的开放阅读框（ORF）区域。基因序列分析表明，这两个基因在PtG和PtY中均相同。系统发育分析表明，PtFIT与调控缺铁反应的bHLH基因聚类在一起，而PtIRO与另一组通过非FIT依赖途径调控缺铁反应的bHLH基因聚类在一起。组织特异性表达分析表明，在所有检测的组织中，仅在根中检测到PtFIT，而在所有检测的组织中很少检测到PtIRO。实时PCR表明，在缺铁条件下根中PtFIT上调。在PtG中检测到的PtFIT转录本水平高于PtY。Pearson相关系数计算表明，PtG中PtFIT与PtIRT1之间存在强正相关（r = 0.94）。这表明PtG对缺铁的耐受性可能受PtFIT依赖的反应途径调控。PtFIT转基因杨树植株对缺铁的反应中PtFIT和PtIRT1的表达水平增加。一个PtFIT转基因株系（TL2）在缺铁条件下比对照植株表现出增强的缺铁耐受性，叶绿素含量和Chl a/b比值更高，表明PtFIT参与了杨树的缺铁反应。这些结果将为理解木本植物缺铁反应机制提供有用信息。
