Preliminary Research On Transcriptional Regulation Of Citrus CitNI5 And CitMYB52 In Sucrose Metabolism

Sucrose plays important roles in plant growth and development regulation.For citrus,sucrose contributed to fruit flavor as well.Neutral/alkaline invertase irreversibly catabolized sucrose into glucose and fructose,and which can be divided into α group and β group.At present,information of citrus NI and its physiological function remain unclear.In the present study,we have analyzed the content of sucrose、glucose、fructose as well as gene expression profiles of NI during fruit development stages(60 d、90 d、120 d、150 d、180 d)of‘Miyagawa wase’and‘Ponkan’fruits.Morever,preliminary mechanism of transcriptional regulation of NI on sucrose metabolism was studied.The main results are as follows:1.Identification of citrus NI.Eight NI genes,named CitNI1-CitNI8,were identified in citrus genome database by blasting amino acid sequence of NI of arabidopsis and tomato.Bioinformatics analysis of citrus NI indicated that CitNI1、CitNI3、CitNI4、CitNI6、CitNI7 belong to α group and CitNI2、CitNI5、CitNI8 belong to β group.2.CitNI5 was negatively correlated with sucrose accumulation.Sucrose gradually accumulated during ‘Miyagawa wase’and‘Ponkan’fruits development stages.The gene expression profiles of citrus NI genes indicated that CitNI5、CitNI6 showed down-regulation and CitNI7 showed up-regulation pattern,while CitNI2、CitNI3、CitNI4 showed no significant changes.In addition,CitNI6 and CitNI7 encoded the same protein while showed reverse expression pattern,which needs to be further clarified.Functional analysis of CitNI5 was performed by yeast strain SEY2102 and the results showed that CitNI5 paly significant roles in sucrose degradation.Combined with the transcriptome analysis in our previous reports,CitNI5 was negatively correlated with sucrose accumulation,thus CitNI5 was selected for further study.3.Transcription factor CitMYB52 could negatively regulate CitNI5 by directly binding to CitNI5 promoter.The transcriptome analysis and dual-luciferase experiment suggested that CitMYB52 significantly repressed CitNI5 promoter activity,with 1/2 fold reduction.Electrophoretic mobility shift assay implicated that CitMYB52 can bind to CitNI5 promoter via core element ATTGTC.Thus,we concluded that CitMYB52 probably inhibited sucrose degradation by regulating CitNI5 via binding to CitNI5’s promoter.