Genome-Wide Identification and Comparison of Cysteine Proteases in the Pollen Coat and Other Tissues in Maize.

Yanhua Li,Wei Wang,Man Zhang,Liangjie Niu,Claudia Faleri,Giampiero Cai,Xiaolin Wu,Hui Liu,Fuju Tai

doi:10.3389/fpls.2021.709534

Yanhua Li, Wei Wang + Show 7 more

Open Access

https://doi.org/10.3389/fpls.2021.709534

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Abstract

Cysteine proteases, belonging to the C1-papain family, play a major role in plant growth and development, senescence, and immunity. There is evidence to suggest that pollen cysteine protease (CP) (ZmCP03) is involved in regulating the anther development and pollen formation in maize. However, there is no report on the genome-wide identification and comparison of CPs in the pollen coat and other tissues in maize. In this study, a total of 38 homologous genes of ZmCP03 in maize were identified. Subsequently, protein motifs, conserved domains, gene structures, and duplication patterns of 39 CPs are analyzed to explore their evolutionary relationship and potential functions. The cis-elements were identified in the upstream sequence of 39 CPs, especially those that are related to regulating growth and development and responding to environmental stresses and hormones. The expression patterns of these genes displayed remarked difference at a tissue or organ level in maize based on the available transcriptome data in the public database. Quantitative reverse transcription PCR (RT-qPCR) analysis showed that ZmCP03 was preferably expressed at a high level in maize pollen. Analyses by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot, immunofluorescence and immunogold electron microscopy all validated the cellular localization of ZmCP03 in both the pollen coat and pollen cytoplasm. In addition, 142 CP genes from Arabidopsis (Arabidopsis thaliana), rice (Oryza sativa) and cotton (Gossypium hirsutum), together with 39 maize CPs, were retrieved to analyze their evolution by comparing with orthologous genes. The results suggested that ZmCP03 was relatively conservative and stable during evolution. This study may provide a referential evidence on the function of ZmCP03 in pollen development and germination in maize.

Highlights

The pollen coat is the outermost surface of pollen grains that contain the haploid male gametes and actively participates in the pollination and fertilization in plants (Zhang et al, 2016)
The information about the protein length, molecular weights (MW), pI, and grand average of hydropathy (GRAVY) values of 39 maize cysteine protease (CP) proteins is listed in Table 1, and the nucleotide and amino acid sequences are provided in Supplementary Dataset 1
A total of 142 CP genes were identified in three plant species (Arabidopsis, cotton, and rice) as papain-like cysteine proteases

Summary

Introduction

The pollen coat is the outermost surface of pollen grains that contain the haploid male gametes and actively participates in the pollination and fertilization in plants (Zhang et al, 2016). The pollen coat can protect pollen grains from dehydration during pollen release and germination in the stigmatic surface (Edlund et al, 2004; Murphy, 2006; Quilichini et al, 2015; Wu et al, 2015; Zhang et al, 2016). Two pollen coat rich-proteins, β-glucanase and xylanase, have been proved to regulate pollen germination and tube growth (Suen et al, 2003; Suen and Huang, 2007). Proteomic and bioinformatics analyses have implicated the important role of many functional-unknown pollen coat-derived proteins in maize (Gong et al, 2015; Wu et al, 2015) and rice (Dai et al, 2006). High-throughput sequencing and bioinformatic analyses have provided comprehensive perspectives in exploring the roles of pollen coat-derived proteins in cotton (Yang et al, 2020)

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