Plant & Animal Genomes XV Conference

January 13-17, 2007
Town & Country Convention Center
San Diego, CA

Research On The Molecular Mechanism Of Flesh Color Mutant Of Sweet Orange

Xiuxin Deng , Nengguo Tao , Qing Liu , Junli Ye , Yunjiang Cheng , Wenwu Guo

  National Key Lab. for Genetic Improvment of Crops,Huazhong Agricultural University, Shizishan street No.1, Wuhan, Hubei province, P.R.China

Bud mutation is a common phenomenon in fruit crops including citrus. Spontaneous mutation provides an import channel for citrus variety selection, and special materials for functional genomics research also. Understanding the mechanism of changed traits on molecular level will enhance the genetic improvement. More than 20 mutants of citrus were found in the past years and 4 of them were registered as cultivars after agronomic evaluation in the past five years. Two mutants of sweet orange with pink flesh from Washington navel orange and Anliu sweet orange respectively were used for our research, aiming at explanation of the red color variation. HPLC analysis verified that the pink color in both mutants was resulted from the accumulation of lycopene, an intermediate product during the carotenoid biosynthesis pathway. The contents of lycopene in both mutants (MT) were much higher than its wild types (WT). However, the types of carotenoids during the pathway did not show difference between the mutant and wild types; as indicated that the structures of the genes encoding the key enzymes during the pathway were normal.The main reason(s) inferring the accumulation of lycopene might be the expression regulation of these genes. Eight genes including PSY, PSD, LCYE and LCYB etc. in the pathway were analyzed. Most of them were single copy in both the MT and WT; there were 2 transcripts in LCYB, LCYE, and also other genes. Alternative splicing was found in the MT of navel orange, one of the spliced transcripts cut 14 bps more than the WT; this led to the shifting of code and generated a stop codon earlier than the normal. A SSH library of WT and MT of Anliu sweet orange were constructed and, 6000 clones were randomly selected and analyzed with microarray during the fruit development. Results showed that 1931 of them were up regulated and 2150 down regulated.
Supported by NSFC