CBP60g Negatively Regulates Anthocyanin Accumulation And Enhances Sensitivity To Calcium Of Arabidopsis Thaliana

Anthocyanins,a kind of flavonoid,normally accumulate in the flowers and fruits and make them colorful,and with great applications in pigmentation,anti-oxidant,UV-light protection and boost pollination.Anthocyanin accumulation is regulated via different temporal and spatial expression of anthocyanin regulatory and biosynthetic genes.Signalling pathways such as illumination intensity,sucrose,phytohormones and calcium signal could also regulate anthocyanin synthesis.The calcium concentration of Arabidopsis is coordinated by a network of transporters.The Ca²⁺/H⁺transporter CAX1?Cation Exchanger 1?and CAX3 are important regulators of cytosolic Ca²⁺levels localized to the tonoplast.CBP60g,a calmodulin binding protein,has previously been confirmed to have a role in pathogen resistance,drought tolerance and ABA sensitivity.In our previous research,high level of CBP60g in Arabidopsis reduced anthocyanin biosynthesis and increased sensitivity to calcium chloride.In this study,the above obderved phenotype were further studied and the results as follows:1.Overexpression of CBP60g repressed anthocyanin accumulation in Arabidopsis.In addition,anthocyanin accumulation induced by drought,sucrose and kinetin has also been inhibited.Histochemical GUS staining showed that the expression pattern of CBP60g was in accordance with the anthocyanin accumulation tissues.2.Real-time qPCR analysis revealed that the anthocyanin biosynthetic genes CHS,CHI and DFR,as well as two members of MBW complex,PAP1,a MYB transcription factor,and TT8,a bHLH transcriptioin factor,were all down-regulated in the overexpression lines,indicate that CBP60g is a negative regulator ofanthocyanin accumulation.3.Overexpression of CBP60g resulted in abnormal phenotypes such as dwarf,more branches,shorter primary roots and more lateral roots.The overexpression lines are more sensitive to high concentration of Ca Cl₂ treatment,and has less calcium content in the mesophyll cells compared with wild type.Further study showed that the expression of CAX1 and CAX3 was reduced in the overexpression lines,and Ca²⁺as well as IAA transportation might be affected.4.Calcium induces both CBP60g expression and anthocyanin accumulation,on the contrary,increased CBP60g level in the cells inhibits anthocyanin biosynthesis and Ca²⁺transportation.A model of the regulatory role of CBP60g was proposed in this study.