Non-additive gene regulation in a citrus allotetraploid somatic hybrid between C. reticulata Blanco and C. limon (L.) Burm

Abstract

Polyploid plants often produce new phenotypes, exceeding the range of variability existing in the diploid gene pool. Several hundred citrus allotetraploid hybrids have been created by somatic hybridization. These genotypes are interesting models to study the immediate effects of allopolyploidization on the regulation of gene expression. Here, we report genome-wide gene expression analysis in fruit pulp of a Citrus interspecific somatic allotetraploid between C. reticulata cv 'Willowleaf mandarin' þ C. limon cv 'Eureka lemon', using a Citrus 20K cDNA microarray. Around 4% transcriptome divergence was observed between the two parental species, and 212 and 160 genes were more highly expressed in C. reticulata and C. limon, respectively. Differential expression of certain genes was confirmed by quantitative real-time RT-PCR. A global downregulation of the allotetraploid hybrid transcriptome was observed, as compared with a theoretical mid parent, for the genes displaying interspecific expression divergence between C. reticulata and C. limon. The genes underexpressed in mandarin, as compared with lemon, were also systematically repressed in the allotetraploid. When genes were overexpressed in C. reticulata compared with C. limon, the distribution of allotetraploid gene expression was far more balanced. Cluster analysis on the basis of gene expression clearly indicated the hybrid was much closer to C. reticulata than to C. limon. These results suggest there is a global dominance of the mandarin transcriptome, in consistence with our previous studies on aromatic compounds and proteomics. Interspecific differentiation of gene expression and non-additive gene regulation involved various biological pathways and different cellular components.

Quantitative Trait Loci (QTL) Analysis of Carotenoid Content in Citrus Fruit

“…It is likely that the wide variation in carotenoid contents among the progeny could be used to generate recombinants with markedly increased carotenoid contents. Analysis of gene expression related to carotenoid metabolism in a mandarin + lemon allotetraploid somatic hybrid (Bassene et al, 2010) also suggested that new combinations of genotypes of different loci could generate progeny with altered carotenoid contents. In that study, lemon juice sacs contained only low levels of B-Car and B-Cry, whereas B-Cry was the major component of carotenoids in mandarin juice sacs, which also contained high levels of other carotenoid components such as Phy, B-car, Vios, and so on.…”

Citrus genomics

“…Moreover, 14 and 29 % spots of the C. deliciosa + C. aurantifolia and C. deliciosa + F. margarita hybrids, respectively, were not encountered in their parental genotypes, suggesting a derepression of these genes in the allotetraploids. Recently, genome-wide gene expression analysis on fruit pulp of a Citrus interspecific somatic allotetraploid between C. reticulata cv 'Willowleaf' mandarin + C. limon cv 'Eureka lemon' was done using a Citrus 20K cDNA microarray (Bassene et al 2010). About 4 % transcriptome divergence was observed between the two parental species, and 212 and 160 genes were highly expressed in C. reticulata and C. limon, respectively.…”

Genetic and Epigenetic Changes in Somatic Hybrid Introgression Lines Between Wheat and Tall Wheatgrass

“…It has been successfully exploited in bread wheat to transfer chromosomal segments from a number of related species Xiang et al 2003Xiang et al , 2004Cheng et al 2004;Zhou and Xia 2005;Xia 2009). More importantly, asymmetric somatic hybridization offers smaller alien chromatin introgression, thereby overcoming a significant problem in wheat sexual hybrids where the Ph1 gene prevents homeologous recombination (Griffiths et al 2006).Newly synthesized allopolyploids have provided an opportunity to explore the nature of the genetic and epigenetic changes triggered by polyploidization (Song et al 1995;Comai et al 2000;Ozkan et al 2001;Shaked et al 2001;Madlung et al 2002;Han et al 2003;Ma et al 2004;Wang et al 2004a;Salmon et al 2005;Tate et al 2006;Bassene et al 2010;Xu et al 2014), although a few allopolyploids were not accompanied with such changes (Liu et al 2001). Experimental results indicate that the majority of events are highly reproducible (Bento et al 2010).…”