Research Article

Identification of Maize Aquaporin Gene ZmPIP4c as a Signature of C4 Traits  

Xiang Li1,2 , Yuling Liang2 , Zhiying Ma1 , Zheng Liu1
1 State Key Laboratory of Crop Improvement and Regulation in North China, College of Agriculture, Hebei Agricultural University, Baoding, 071001
2 College of Life Science, Hebei University, Baoding, 071002
Author    Correspondence author
Maize Genomics and Genetics, 2020, Vol. 11, No. 1   
Received: 02 Sep., 2020    Accepted: 07 Sep., 2020    Published: 25 Sep., 2020
© 2020 BioPublisher Publishing Platform
This article was first published in Molecular Plant Breeding in Chinese, and here was authorized to translate and publish the paper in English under the terms of Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract

As a water transmembrane transporter, aquaporin can not only transport water in plants, but also transport small molecules such as CO2 and H2O2, thus affecting physiological processes such as photosynthesis and so on. Although photosynthesis is critical to plant growth, the photosynthetic mechanisms of C3 plants are different from that of C4 plants as compared with C3 leaves, C4 leaves have typical Kranz structure and possess larger and well-developed bundle sheath cells which is favorable for water storage. We therefore performed bioinformatic and gene expression analyses on C4 maize aquaporin, and identified a gene called ZmPIP4c which shows high specific expression in bundle sheath cells in leaves. thus is conducive to water transport into sheath cells and to balance the water supply in mesophyll cells. Further expression analysis on the ZmPIP4c along leaf gradient revealed that the expression trend of this gene was not only consistent with that of C4 marker gene - NAD-malic enzyme gene (NAD-ME), a gene usually used to screen C4 photosynthesis related transcripts, but also consistent with other C4 genes such as phosphoenolpyruvate carboxylase gene (PEPC) and carbonic anhydrase gene (CA). The expressions of these genes all showed gradual increase from leaf base to leaf tip, suggesting that ZmPIP4c is a signature of C4 traits. In addition, ZmPIP4c, NAD-ME, PEPC and CA also showed similar expression trends under the regulation of circadian rhythm, indicating that ZmPIP4c can provide optimal water environment for the efficient operation of C4 cycle in bundle sheath cells under light, and avoid energy and water waste under dark. Moreover, the expressions of ZmPIP4c gene and of mesophyll-specifically-expressed genes, PEPC and CA, were all down-regulated under salt stress. As there exists water conduction signal between bundle sheath cells and mesophyll cells, down-regulation of ZmPIP4c gene may change the inner water solution environment within mesophyll cells, thereafter affecting the expresions of PEPC and CA genes. In brief, our study on ZmPIP4c gene of maize provides us a signature gene to study new C4 traits that have not been reported yet, and helps us to understand the molecular mechanism how the cell-specific aquaporin gene mediates the C4 cycle.

Keywords
Maize; C4 photosynthesis; Aquaporin protein; Bioinformatics; Gene expression
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