Molecular Identification And Functional Analysis Of The Family Of Magnesium Ion Transporter In Pepper(Capsicum Annuum L.)

Magnesium(Mg²⁺)is an important element for plant growth,which plays an essential role in the growth and development of plants.The transportation and homeostasis of magnesium ion in plants are mainly maintained by the magnesium ion transporter MRS2/MGT（mitochondrial RNA splicing 2/Magnesium Transporter）.Pepper（Capsicum annuum L.）is one of the most important vegetable crops around the world.We studied the molecular identification and functional analysis of the family of magnesium ion transporter in pepper（Capsicum annuum L.）,and the main results were as follows.1.The results of the bioinformatics of MGTs in pepper（Capsicum annuum L.）showed that the putative MGTs including 9 CaMGTs,6Capang MGTs,and 10 Capana MGTs were identified from the three major sequenced genomes（CM334,glabriusculum,and zunla）of Capsicum annuum,respectively.And the phylogeny,gene structure,conserved motifs and chromosomal position of these MGTs were further analysized.They were divided into five different groups through phylogenetic analysis,which were obviously homologous to the MRS2/MGT gene from Arabidopsis and rice.2.The CDS（Coding sequence）of all CaMGTs were successfully cloned from the CM334 genome.The result of the complementation test of Salmonella typhimurium strain mutant mm281 showed that CaMGTs can mediate the absorption and transport of Mg²⁺.The affinity with Mg²⁺of CaMGTs were different,in which both CaMGT1.2 and CaMGT4.2might be high-affinity proteins,but CaMGT3,CaMGT4.1 and CaMGT10might be low-affinity ones.3.Tissue expression pattern analysis results showed that CaMGTs were expressed in all the tested tissues and these genes showed specific expression patterns.All CaMGTs were generally expressed at a extremely low level in the stem.A highest level of CaMGT10 and CaMGT7 were expressed in leaves and flowers,respectively.Both CaMGT1.1 and CaMGT4.1 were mainly expressed in leaves and flowers.And the significance level of the difference of these two genes expression in all the tested tissues were relatively consistant,but the remaining CaMGTs were different.These results suggests that CaMGTs may participate in the unique physiological metabolism of different organs.4.Analysis of the circadian rhythm expression patterns of CaMGT10showed that the peak of expression always appeared at the beginning of daylight,and the trough emerged at the end of daylight during the cycle of 24 hours.It was consistent with the reported circadian rhythms from rice MGT（Os MGT3）and mazie MGT（Zm MGT12）.Under different Mg²⁺concentration treatment conditions,the change of CaMGT10 expression was consistent with that of Mg²⁺concentration.High concentration of Mg²⁺induced up-regulation of CaMGT10 expression.Conversely,expression of the gene was down-regulated.Meanwhile,changes of pepper SPAD（Soil and Plant Analyzer Development）value（chlorophyll content）,photosynthetic rate,biomass and phenotype under different Mg²⁺concentrations were similar to that of transcription level of CaMGT10,indicating that CaMGT10 can mediate the absorption and transport of Mg²⁺in pepper.