Genome-wide Identification And Expression Analysis Of Purple Acid Phosphatase In Maize

Phosphorus is one of the macronutrients for plant growth and development. Most of phosphorus exists in the soil as organic state which can not be absorbed or utilized directly by plant. Purple acid phosphatase (PAP) is the member of the metallophosphoesterase family which was produced and excreted to mobilize inorganic phosphorus (Pi) from organic compounds for plants. PAP gene families of Arabidopsis, rice and soybeans have been identified. In this study, we identified PAP gene family in the maize genome through bioinformatics. The gene structure, the chromosomal distribution, the protein properties and the evolutionary relationship of maize PAP genes have been analyzed. In order to elucidate the potential function of PAP, gene cloning, semi-quantitative, RT-PCR and subcellular localization were then carried out. The main results were as follows:(1) Based on Blastp search,25 PAP genes were identified in maize genome aaiaoase which distributed on eight chromosomes except 5 and 8. The analysis of 25 PAP amino acid sequences showed that the length ranged from 253 to 594, the molecular weight ranged from 31.833 kDa to 67.230 kDa and the pI ranged from 5.21 to 7.07. The putative protein domains analysis showed that 19 ZmPAP contained the five conserved motifs and seven metal-binding residues which were the characteristic of PAP metalloesterase. The phylogenetic relationship analysis showed that maize PAPs expressed a closer relationship to rice PAPs.(2) The expression analysis of ZmPAP genes in maize 178 and 9782 roots and leaves under phosphorus deficiency were performed by Semi-quantitative. The results suggested that among eight ZmPAPs seven showed differential expression under low Pi stress. ZmPAP5b, ZmPAP20d and ZmPAP26a genes were detected and exhibited different expression profiles in different organs. ZmPAP5b showed decreased level of expression in roots and increased level of expression in leaves, and ZmPAP20b and ZmPAP26b were opposite of ZmPAP5b. ZmPAP5c and ZmPAP26b were detected only in 9782 leaves and showed increased expression under Pi deficiency. ZmPAP27c was down-regulated in 178 and 9782 leaves under low Pi stress.(3) According to the results of Semi-quantitative, ZmPAP5b、ZmPAP5c、ZmPAP26a、 ZmPAP26b and ZmPAP27c were isolated from maize inbred line 178 seedlings with the complete coding region of about 1300 bp in length. The analysis of amino acid residues showed that ZmPAP5c lose the second block which contains two metal-ligating residues D and Y, and the other four contain five block (DXG/GDXXY/GNHE(D)/VXXH/GHXH).(4) qRT-PCR was used to detect the expression profile of PAP genes in roots and leaves of maize inbred line 178 and 9782. ZmPAP26a and ZmPAP26b showed decreased level of expression in leaves of 9782. ZmPAP27c showed differential expression in leavess of both 178 and 9782, and appeared the maximal level at 12 h time point. The expression of ZmPAP5b was inhibited in roots and leaves of two materials, and that of ZmPAPSc only was induced or increased in leaves of 178 at 12 h time point.(5)Subcellular location was involved in below two processes:constructing a fusion expression vector of pAcGFP1-N1-ZmPAP26a and pAcGFP1-Nl-ZmPAP27c after cloning from 178 cDNA and sequencing, and transforming the two recombinant plasmid into onion epidermal cells. The products of ZmPAP26a and ZmPAP27c were located in the cell membrane.(6)The p-NPP was used to analysis the APase activity in roots and leaves of 178 and 9782 under Pi starvation. The results showed that the APase activity of roots was higher than leaves under low Pi stress, and the activity in 178 roots was more sensitive than 9782 roots. Moreover, the activity of new leaves was higher than old in 178,9782 was opposite.