Identification of Tea Plant Purple Acid Phosphatase Genes and Their Expression Responses to Excess Iron.

Chaoyan Yin,Wenfeng Li,Fei Wang,Yanming Fang,Huiqin Fan

doi:10.3390/ijms20081954

Chaoyan Yin, Wenfeng Li + Show 3 more

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https://doi.org/10.3390/ijms20081954

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Abstract

Purple acid phosphatase (PAP) encoding genes are a multigene family. PAPs require iron (Fe) to exert their functions that are involved in diverse biological roles including Fe homeostasis. However, the possible roles of PAPs in response to excess Fe remain unknown. In this study, we attempted to understand the regulation of PAPs by excess Fe in tea plant (Camellia sinensis). A genome-wide investigation of PAP encoding genes identified 19 CsPAP members based on the conserved motifs. The phylogenetic analysis showed that PAPs could be clustered into four groups, of which group II contained two specific cysteine-containing motifs “GGECGV” and “YERTC”. To explore the expression patterns of CsPAP genes in response to excessive Fe supply, RNA-sequencing (RNA-seq) analyses were performed to compare their transcript abundances between tea plants that are grown under normal and high iron conditions, respectively. 17 members were shown to be transcribed in both roots and leaves. When supplied with a high amount of iron, the expression levels of four genes were significantly changed. Of which, CsPAP15a, CsPAP23 and CsPAP27c were shown as downregulated, while the highly expressed CsPAP10a was upregulated. Moreover, CsPAP23 was found to be alternatively spliced, suggesting its post-transcriptional regulation. The present work implicates that some CsPAP genes could be associated with the responses of tea plants to the iron regime, which may offer a new direction towards a further understanding of iron homeostasis and provide the potential approaches for crop improvement in terms of iron biofortification.

Highlights

Purple acid phosphatases (PAPs) are metallohydrolases that use a binuclear metal ion center to catalyze the hydrolysis of a broad range of phosphorylated substrates from acidic to neutral pH [1]
Further searches using the protein sequences of the 29 Arabidopsis PAPs as the queries with BLASTP at the tea plant genome database website resulted in the retrieval of 53 predicted PAPs based on the similarity of protein sequences with E value ≤ e−10. 12 duplicates were further removed, which resulted in 62 potential PAPs in total
Five out of the 62-candidate tea plant PAPs lack three of the five blocks. Even though their overall amino acid sequences exhibited significant levels of homology to plant known PAPs when BLASTing in National Center for Biotechnology Information (NCBI), they were considered as inactive PAPs because of the significant lack of active sites and incomplete metallophos domain that conserved in purple acid phosphatases of the metallophosphatase superfamily, which were identified by the Phoibus program (Table 2)

Summary

Introduction

Purple acid phosphatases (PAPs) are metallohydrolases that use a binuclear metal ion center to catalyze the hydrolysis of a broad range of phosphorylated substrates from acidic to neutral pH [1]. The charge transitions between a tyrosine amino acid and ferric ion (Fe(III) confer the purple color to the PAPs [2]. PAPs from different species have conserved structural and sequence motifs. The genome-wide PAP encoding genes have been identified in model plant Arabidopsis (Arabidopsis thaliana) and important crops including rice (Oryza sativa), soybean (Glycine max), maize (Zea mays), chickpea (Cicer arietnum) and physic nut (Jatropha curcas) based on the presence of conserved sequence motifs [3,4,5,6,7,8]. The number of putative PAP isozymes has been predicted to be 26 in rice, 35 in soybean, 33 in maize and 25 in chickpea [3,4,5,6]

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