Mapping quantitative trait loci for tissue culture response in VCS3M-DH population of Brassica rapa

TaTCP-1, a Novel Regeneration-Related Gene Involved in the Molecular Regulation of Somatic Embryogenesis in Wheat (Triticum aestivum L.)

The lower regeneration rate of wheat calli is the main factor restricting the development of transgenic wheat plants. Therefore, improving the regeneration rate of wheat callus is a precondition for developing genetic engineering-based wheat breeding approaches. In the present study, we explored the molecular mechanism of wheat regeneration and aimed to establish an efficient system for transgenic wheat. We isolated and identified a regeneration-related gene, TaTCP-1 (KC808517), from wheat cultivar Lunxuan 987. Sequence analysis revealed that the ORF of TaTCP-1 was 1623bp long encoding 540 amino acids. The TaTCP-1 gene was expressed in various wheat tissues. Further, the level of TaTCP-1 expression was higher in calli and increased gradually with increasing callus induction time, reaching a peak on the 11th day after induction. Moreover, the expression level of TaTCP-1 was higher in embryogenic calli than in non-embryonic calli. The TaTCP-1 protein was localized to the nucleus, cytoplasm, and cell membrane. The callus regeneration rate of wheat plants transformed with TaTCP-1-RNAi reduced by 85.09%. In contrast, it increased by 14.43% in plants overexpressing TaTCP-1. In conclusion, our results showed that TaTCP-1 played a vital role in promoting wheat regeneration, and regulated the somatic embryogenesis of wheat. These results may have implications in the genetic engineering of wheat for improved wheat production.

Genetic analysis and identification of a candidate gene associated with in vitro regeneration ability of cucumber

Candidate genes associated with in vitro regeneration were identified in cucumber. The ability to regenerate shoots or whole plants from differentiated plant tissues is essential for plant transformation. In cucumber (Cucumis sativus L.), regeneration ability varies considerably across accessions, but the genetic mechanism has not yet been demonstrated. In the present study, 148 recombinant inbred lines and a core collection were examined to identify candidate genes involved in cucumber regeneration. Four QTL for cotyledon regeneration that explained 9.7-16.6% of the phenotypic variation in regeneration were identified on cucumber chromosomes 1, 3, and 6. The loci Fcrms1.1 and Fcrms₊1.1 were consistently detected in the same genetic interval on two regeneration media. A genome-wide association study revealed 18 SNPs (- log(p) > 5) significantly associated with cotyledon regeneration. Three candidate genes in this region were identified. RT-PCR analyses revealed that Csa1G642540 was significantly more highly expressed in genotypes with high cotyledon regeneration rates than in those with low regeneration. The Csa1G642540 CDS driven by its native promoter was transformed into cucumber line 9110Gt; molecular analyses showed that the T-DNA had integrated into the genomes of 8.6% of regenerated plantlets. The seeds from T₀ plants expressing Csa1G642540 were tested for regeneration from cotyledon explants, and the segregate ratio in regeneration frequency is 3:1. The AT3G44110.1, the homologue gene of Csa1G642540 in Arabidopsis, has been reported as PM H⁺-ATPase activity regulation, integrating flowering signals and enlarging meristem function. These results demonstrate that Csa1G642540 might play an important role in regeneration in cucumber and could serve as a selectable marker for regeneration from cotyledons.

Genetic dissection of adventitious shoot regeneration in roses by employing genome-wide association studies

We analysed the capacity to regenerate adventitious shoots in 96 rose genotypes and found 88 SNP markers associated with QTLs, some of which are derived from candidate genes for shoot regeneration. In an association panel of 96 rose genotypes previously analysed for petal colour, we conducted a genome-wide association study on the capacity of leaf petioles for direct shoot regeneration. Shoot regeneration rate and shoot ratio (number of shoots/total number of explants) were used as phenotypic descriptors for regeneration capacity. Two independent experiments were carried out with six replicates of ten explants each. We found significant variation between the genotypes ranging from 0.88 to 88.33% for the regeneration rate and from 0.008 to 1.2 for the shoot ratio, which exceeded the rates reported so far. Furthermore, we found 88 SNP markers associated with either the shoot regeneration rate or the shoot ratio. In this association analysis, we found 12 SNP markers from ESTs (expressed sequence tags) matching known candidate genes that are involved in shoot morphogenesis. The best markers explained more than 51% of the variance in the shoot regeneration rate and more than 0.65 of the variance in the shoot regeneration ratio between the homozygote marker classes. The genes underlying some of the best markers such as a GT-transcription factor or an LRR receptor-like protein kinase are novel candidate genes putatively involved in the observed phenotypic differences. The associated markers were mapped to the closely related genome of Fragaria vesca and revealed many distinct clusters, which also comprised the known candidate genes that functioned in the organogenesis of plant shoots. However, the validation of candidate genes and their functional relationship to shoot regeneration require further analysis in independent rose populations and functional analyses.

Identification and mapping of a novel dominant resistance gene, TuRB07 to Turnip mosaic virus in Brassica rapa

A novel dominant resistance gene, TuRB07, was found to confer resistance to an isolate of TuMV strain C4 in B. rapa line VC1 and mapped on the top of chromosome A06. The inheritance of resistance to Turnip mosaic virus in Brassica rapa was investigated by crossing the resistant line, VC1 with the susceptible line, SR5, and genotyping and phenotyping diverse progenies derived from this cross. Both a doubled haploid population, VCS3M-DH, an F2 and two BC1 (F1 × VC1 and F1 × SR5) populations were created. Population tests revealed that the resistance to the TuMV C4 isolate in B. rapa is controlled by a single dominant gene. This resistance gene, TuRB07 was positioned on the top of linkage group A06 of the B. rapa genome through bulk segregation analysis and fine mapping recombinants in three doubled haploid- and one backcross population using microsatellite markers developed from BAC end sequences. Within the region between the two closely linked markers flanking TuRB07, H132A24-s1, and KS10960, in the Chiifu reference genome, two genes encoding nucleotide-binding site and leucine-rich repeat proteins with a coiled-coil motif (CC-NBS-LRR), Bra018862 and Bra018863 were identified as candidate resistance genes. The gene Bra018862 is truncated, but the gene Bra018863 has all the domains to function. Furthermore, the analysis of structural variation using resequencing data of VC1 and SR5 revealed that Bra018863 might be a functional gene because the gene has no structural variation in the resistant line VC1 when compared with Chiifu, whereas at the other NBS-LRR genes large deletions were identified in the resistant line. Allelic differences of Bra018863 were found between VC1 and SR5, supporting the notion that this gene is a putative candidate gene for the virus resistance.