Analysis of genetic diversity in cytoplasmic male sterility, and association of mitochondrial genes with petaloid-type cytoplasmic male sterility in tuber mustard (Brassica juncea var. tumida Tsen et Lee)

Protoplast Technology and Somatic Hybridisation in the Family Apiaceae

Species of the family Apiaceae occupy a major market share but are hitherto dependent on open pollinated cultivars. This results in a lack of production uniformity and reduced quality that has fostered hybrid seed production. The difficulty in flower emasculation led breeders to use biotechnology approaches including somatic hybridization. We discuss the use of protoplast technology for the development of somatic hybrids, cybrids and in-vitro breeding of commercial traits such as CMS (cytoplasmic male sterility), GMS (genetic male sterility) and EGMS (environment-sensitive genic male sterility). The molecular mechanism(s) underlying CMS and its candidate genes are also discussed. Cybridization strategies based on enucleation (Gamma rays, X-rays and UV rays) and metabolically arresting protoplasts with chemicals such as iodoacetamide or iodoacetate are reviewed. Differential fluorescence staining of fused protoplast as routinely used can be replaced by new tagging approaches using non-toxic proteins. Here, we focused on the initial plant materials and tissue sources for protoplast isolation, the various digestion enzyme mixtures tested, and on the understanding of cell wall re-generation, all of which intervene in somatic hybrids regeneration. Although there are no alternatives to somatic hybridization, various approaches also discussed are emerging, viz., robotic platforms, artificial intelligence, in recent breeding programs for trait identification and selection.

Development of molecular markers specific to petaloid-type cytoplasmic male sterility in tuber mustard (Brassica juncea var. tumida Tsen et Lee)

To establish a simple and rapid method for isolating mitochondrial DNA (mtDNA) from Brassica vegetables, the effects of different factors on mtDNA extraction were investigated firstly. A new protocol includes five steps: organelle isolation, deoxyribonuclease treatment, lysis, RNase treatment, and deproteinization. Results indicate that a 15 min-lysis time can achieve higher mtDNA yields from etiolated seedlings. Moreover, it is found that the inflorescence of the cytoplasmic male sterile (CMS) line is unfit for the isolation of mtDNA. The mtDNA isolated using this method is intact and pure, and can be used for further molecular analysis. Subsequently, the genomic and transcriptional differences of atps and coxs genes on the mitochondria between the petaloid-type CMS line and its maintainer line have been identified. RFLP analysis revealed that out of the five atps and three coxs genes, except of atp4 and cox3, the others mtDNA protein coding genes exhibited polymorphisms, respectively. This results suggest that atps and coxs genes are located in a long mtDNA fragment, and the mtDNA evolves rapidly in structure between the CMS line and its maintainer line in tuber muster. Northern blot analysis showed that the expression level of these genes in flower bud is higher than that of leaf and flower, and that, alternative splicing have been found among the atp6, atp8 and cox3 genes, respectively. Our results modified a efficient protocol for isolating the mtDNA, and provided some novel molecular markers indicating the CMS trait in tuber mustard. The comparative analysis presented in this study allows a more comprehensive understanding of the molecular mechanism on CMS in Brassica crops.

A GA-insensitive dwarf mutant of Brassica napus L. correlated with mutation in pyrimidine box in the promoter of GID1

A dwarf mutant from Brassica napus, namely NDF-1, which was derived from a high doubled haploid (DH) line '3529'(Brassica napus L.) of which seeds were jointly treated with chemical inducers and fast neutron bombardment, was revealed that dwarfism is under the control of a major gene(designated as ndf1) with a mainly additive effect and non-significant dominance effect. The germination and hypocotyls elongation response of dwarf mutants after exogenous GA and uniconazol application showed NDF-1 was a gibberellin insensitive dwarf. We cloned the Brassica napus GID1 gene, named BnGID1, and found it was the ortholog of AtGID1a. The sequence blasting of the BnGID1 genes from NDF-1 and wild type showed there was no mutant in the gene. But the quantitative RT-PCR analysis of GID1 EST pointed out the mutation was caused by the low-level expression of BnGID1 gene. After sequenced the BnGID1 gene's upstream, we found three bases mutated in the pyrimidine box (P-box) of the BnGID1 promoter, which is linkage with the dwarf mutant.