An uncleaved signal peptide directs the Malus xiaojinensis iron transporter protein Mx IRT1 into the ER for the PM secretory pathway.
Malus xiaojinensis iron-regulated transporter 1 (Mx IRT1) is a highly effective inducible iron transporter in the iron efficient plant Malus xiaojinensis. As a multi-pass integral plasma membrane (PM) protein, Mx IRT1 is predicted to consist of eight transmembrane domains, with a putative N-terminal signal peptide (SP) of 1-29 amino acids. To explore the role of the putative SP, constructs expressing Mx IRT1 (with an intact SP) and Mx DsIRT1 (with a deleted SP) were prepared for expression in Arabidopsis and in yeast. Mx IRT1 could rescue the iron-deficiency phenotype of an Arabidopsis irt1 mutant, and complement the iron-limited growth defect of the yeast mutant DEY 1453 (fet3fet4). Furthermore, fluorescence analysis indicated that a chimeric Mx IRT1-eGFP (enhanced Green Fluorescent Protein) construct was translocated into the ER (Endoplasmic reticulum) for the PM sorting pathway. In contrast, the SP-deleted Mx DsIRT1 could not rescue either of the mutant phenotypes, nor direct transport of the GFP signal into the ER. Interestingly, immunoblot analysis indicated that the SP was not cleaved from the mature protein following transport into the ER. Taken together, data presented here provides strong evidence that an uncleaved SP determines ER-targeting of Mx IRT1 during the initial sorting stage, thereby enabling the subsequent transport and integration of this protein into the PM for its crucial role in iron uptake.
College of Life Science, Capital Normal University, Beijing 100048, China. zhangpeng_cnu@163.com.
Peng
P
Zhang
College of Life Science, Capital Normal University, Beijing 100048, China. tansong_1515@163.com.
Song
S
Tan
Department of Biological Sciences, State University of New York, Buffalo, NY 14260, USA. camjob@buffalo.edu.
James O
JO
Berry
School of Life Sciences, Tsinghua University, Beijing 100083, China. lipeng@tsinghua.edu.cn.
Peng
P
Li
College of Life Science, Capital Normal University, Beijing 100048, China. N.Naren@massey.ac.nz.
Na
N
Ren
College of Life Science, Capital Normal University, Beijing 100048, China. lishuanghebei@163.com.
Shuang
S
Li
College of Life Science, Capital Normal University, Beijing 100048, China. ygemouse@163.com.
Guang
G
Yang
College of Life Science, Capital Normal University, Beijing 100048, China. wangweibing14@mails.ucas.ac.cn.
Wei-Bing
WB
Wang
College of Life Science, Capital Normal University, Beijing 100048, China. qixiaoting@cnu.edu.cn.
Xiao-Ting
XT
Qi
College of Life Science, Capital Normal University, Beijing 100048, China. yinlp@cnu.edu.cn.
Li-Ping
LP
Yin
D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D017353:Gene Deletion; D015870:Gene Expression; D007501:Iron / Q000378:metabolism*; D027845:Malus / Q000737:chemistry / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D021382:Protein Sorting Signals; D055571:Secretory Pathway
D002352:Carrier Proteins; D010940:Plant Proteins; D021382:Protein Sorting Signals; D007501:Iron