Utilization of intergeneric somatic hybrids as an index discriminating taxa in the genus Citrus and its related species

Abstract

Embryogenic protoplasts of 'Shogun' mandarin (Citrus reticulata Blanco) were electrically fused with mesophyll protoplasts from Citropsis gabunensis Swing. & M. Kell, and two green embryoids were regenerated after 3 months of culture. Two months after transfer to the regeneration medium, numerous plantlets were obtained from the embryoids. These plants grew vigorously, had well-developed root systems, and exhibited leaf characteristics intermediate to those of the parents. The absolute nuclear genome size of the regenerated plant SH2 (1.75 pg/4C) was the sum of those of the 'Shogun' mandarin (0.75 pg/2C) and C. gabunensis (0.97 pg/2C). The chromosome counts of the young leaves revealed that they were tetraploids (2n=4x=36). Random amplified polymorphic DNA (RAPD) analysis of the two lines (SH1 and SH2) verified their hybridity. Cytoplasmic genome analysis using universal primers reveal that their chloroplast (cp) DNA banding pattern is identical to that of C. gabunensis, while the banding pattern of the mitochondrial (mt) DNA is identical to that of the 'Shogun' mandarin. These somatic hybrids are important materials for investigating the phylogenetic relationships between these two genera in the subfamily Aurantioideae.

Inter-generic mitochondrial genome recombination in somatic hybrids betweenCitrusandPoncirus

“…Several reports have suggested that the mitochondrial genome of the suspension cell parent might play an essential role in hybrid regeneration (for a review see Cabasson et al, 2001). Despite more than 20 cases of inter-generic somatic hybrids between Citrus and Poncirus, with their mtDNA compositions identified by CAPS markers in several cases (Guo et al, 2002;MedinaUrrutia et al, 2004), to our knowledge, only about three-to-five polymorphic mtDNA CAPS primer pairs are available in Citrus, so far (Cheng et al, 2003a;Takami et al, 2005). mtDNA in Citrus somatic hybrids, or cybrids, identified by CAPS has shown suspension cell parental banding patterns, uniformly and without exception; which suggests: (i) that mitochondrial genomes are inherited uni-parentally from the suspension cell parent, as reported by Cabasson et al (2001); or (ii) that the suspension cell parent possesses some preference for inheritance at these loci during protoplast fusion.…”

“…To date, numerous artificial Citrus hybrids have been produced by protoplast fusion, with considerable potential both for theoretical studies and genetic improvement (Grosser et al, 2005;Wu et al, 2005). Genetic diversity analyses using molecular markers such as restriction fragment length polymorphisms (RFLP; Moriguchi et al, 1997;Olivares-Fuster et al, 2005), random amplified polymorphic DNA (RAPD; Medina-Urrutia et al, 2004;Takami et al, 2005), amplified fragment length polymorphisms (AFLPs;Fu et al, 2004), cleaved amplified polymorphic sequences (CAPS;Cheng et al, 2003a;Lotfy et al, 2003;Medina-Urrutia et al, 2004), simple sequence repeats (SSRs; Guo and Grosser, 2005;Xu et al, 2006;Guo et al, 2006), and genomic in situ hybridisation (GISH;Fu et al, 2004) provide powerful approaches for hybrid identification and further genetic analyses. Molecular evidence strongly suggests that the nuclear genome was inherited from both fusion parents in somatic hybrids, and from the mesophyll parent in cybrids; however, the cytoplasmic inheritance pathway is understood only in some cases (reviewed by Cabasson et al, 2001).…”

Progress in plant protoplast research

“…For Citrus fusion, the general consensus is that cpDNA is randomly transmitted; as for mtDNA, nearly all hybrids get theirs from the suspension parents (Fu et al 2004;Guo et al 2004;Takami et al 2005). Guo et al (2007a, b) described cpDNA coexistence in Citrus fusions.…”

GFP expression as an indicator of somatic hybrids between transgenic Satsuma mandarin and calamondin at embryoid stage

“…In citrus breeding, new materials created by somatic hybridization have shown a bright future in new rootstock improvement, triploid seedless cultivar breeding, and creation of diploid cytoplasmic male sterile cybrids Guo et al 2004;Grosser and Gmitter 2005). To date, numerous intergeneric and interspecific citrus somatic hybrids have been recovered via somatic fusion Grosser and Gmitter 2005;Takami et al 2005;Wu et al 2005), including regenerated diploid cybrid plants from over 40 symmetrical fusion combinations Guo et al 2004).…”