Mitochondrial DMA variation in somatic embryogenic cultures ofLarix

Somaclonal Variation During Picea abies and P. omorika Somatic Embryogenesis and Cryopreservation

Embryogenic cultures of plants are exposed to various stress factors bothin vitroand during cryostorage. In order to safely include the plant material obtained by somatic embryogenesis in combination with cryopreservation for breeding programs, it is necessary to monitor its genetic stability. The aim of the present study was the assessment of somaclonal variation in plant material obtained from embryogenic cultures ofPicea abies(L.) Karst. andP. omorika(Pančić) Purk. maintainedin vitroor stored in liquid nitrogen by the pregrowth-dehydration method. The analysis of genetic conformity with using microsatellite markers was performed on cotyledonary somatic embryos (CSE), germinating somatic embryos (GSE) and somatic seedlings (SS), obtained from tissues maintainedin vitroor from recovered embryogenic tissues (ETc) and CSE obtained after cryopreservation. The analysis revealed changes in the DNA of somatic embryogenesis-derived plant material of bothPiceaspp. They were found in plant material from 8 out of 10 tested embryogenic lines ofP. abiesand in 10 out of 19 embryogenic lines ofP. omorikaafterin vitroculture. Changes were also detected in plant material obtained after cryopreservation. Somaclonal variation was observed in ETc and CSE ofP. omorikaand at ETv stage ofP. abies. However, most of the changes were induced at the stage of somatic embryogenesis initiation. These results confirm the need for monitoring the genetic stability of plants obtained by somatic embryogenesis and after cryopreservation for both spruce species.

Progressive erosion of genetic and epigenetic variation in callus-derived cocoa (Theobroma cacao) plants

*Relatively little is known about the timing of genetic and epigenetic forms of somaclonal variation arising from callus growth. We surveyed for both types of change in cocoa (Theobroma cacao) plants regenerated from calli of various ages, and also between tissues from the source trees. *For genetic change, we used 15 single sequence repeat (SSR) markers from four source trees and from 233 regenerated plants. For epigenetic change, we used 386 methylation-sensitive amplified polymorphism (MSAP) markers on leaf and explant (staminode) DNA from two source trees and on leaf DNA from 114 regenerants. *Genetic variation within source trees was limited to one slippage mutation in one leaf. Regenerants were far more variable, with 35% exhibiting at least one mutation. Genetic variation initially accumulated with culture age but subsequently declined. MSAP (epigenetic) profiles diverged between leaf and staminode samples from source trees. Multivariate analysis revealed that leaves from regenerants occupied intermediate eigenspace between leaves and staminodes of source plants but became progressively more similar to source tree leaves with culture age. *Statistical analysis confirmed this rather counterintuitive finding that leaves of 'late regenerants' exhibited significantly less genetic and epigenetic divergence from source leaves than those exposed to short periods of callus growth.

Analysis of genetic stability at SSR loci during somatic embryogenesis in maritime pine (Pinus pinaster)

Somatic embryogenesis (SE) is a propagation tool of particular interest for accelerating the deployment of new high-performance planting stock in multivarietal forestry. However, genetic conformity in in vitro propagated plants should be assessed as early as possible, especially in long-living trees such as conifers. The main objective of this work was to study such conformity based on genetic stability at simple sequence repeat (SSR) loci during somatic embryogenesis in maritime pine (Pinus pinaster Ait.). Embryogenic cell lines (ECLs) subjected to tissue proliferation during 6, 14 or 22 months, as well as emblings regenerated from several ECLs, were analyzed. Genetic variation at seven SSR loci was detected in ECLs under proliferation conditions for all time points, and in 5 out of 52 emblings recovered from somatic embryos. Three of these five emblings showed an abnormal phenotype consisting mainly of plagiotropism and loss of apical dominance. Despite the variation found in somatic embryogenesis-derived plant material, no correlation was established between genetic stability at the analyzed loci and abnormal embling phenotype, present in 64% of the emblings. The use of microsatellites in this work was efficient for monitoring mutation events during the somatic embryogenesis in P. pinaster. These molecular markers should be useful in the implementation of new breeding and deployment strategies for improved trees using SE.

Detection of somaclonal variation of cotton (Gossypium hirsutum) using cytogenetics, flow cytometry and molecular markers

Two protocols of plant regeneration for cotton were adopted in this study, namely, 2, 4-D and kinetin hormone combination and IBA and kinetin hormone combination. Twenty-eight embryogenic cell lines via somatic embryogenesis and 67 regenerated plants from these embryogenic calli were selected and used for random amplified polymorphic DNA (RAPD), simple sequence repeat (SSR), chromosomal number counting, and flow cytometric analysis. The roles of RAPD and SSR markers in detecting somaclonal variation of cotton (Gossypium hirsutum L.) were evaluated. Two cluster analyses were performed to express, in the form of dendrograms, the relationships among the hormone combinations and the genetic variability. Both DNA-based techniques were able to amplify all of the cell clones and regenerated plantlets genomes and relative higher genetic variation could be detected in the culture type with 2, 4-D and kinetin hormone combination. The result suggested that 2, 4-D and kinetin hormone combination could induce relative high somaclonal variation and RAPD and SSR markers are useful in detecting somaclonal variation of regenerated cotton plants via somatic embryogenesis. Chromosome number counting and flow cytometry analysis revealed that the number of chromosomes and ploidy levels were nearly stable in all regenerated plants except two regenerated plantlets (lost 4 and 5 chromosomes, respectively) which meant that cytological changes were not correlated with the frequency of RAPD and SSR polymorphisms. This result also might mean that the cell lines with variation of chromosome numbers were difficult to regenerate plants.

Detection of microsatellite instability during somatic embryogenesis of oak (Quercus robur L.)

Five microsatellite loci (QpZAG1/5, QpZAG9, QpZAG36, MSQ4, MSQ13) were used to test for genetic stability of three somatic embryogenic culture lines of Quercus robur L. and plantlets derived therefrom. DNA variation was detected among somatic embryos within all embryogenic lines, whereas no genetic instability was found among the regenerated plants. Two microsatellite loci revealed variation, and a locus-dependent instability was observed. The most polymorphic and useful microsatellite locus for detecting genetic variation was QpZAG9, with 28.5% of the investigated loci being variable.

Mitochondrial DMA variation in plants regenerated from embryogenic callus cultures of CMS triticale

The mitochondrial DNA (mtDNA) organization of primary hexaploid cytoplasmic male-sterile (CMS) triticale regenerants containing Triticum timopheevi cytoplasm was analysed by hybridization experiments and compared with the mitochondrial genome organization of the corresponding regenerants with maintainer cytoplasm. Callus cultures had been derived from immature embryos, and 623 triticale plants were regenerated via somatic embryogenesis after three to four subcultures. The chondriome of 159 regenerants was investigated with regard to somaclonal variation. Six different mitochondrial gene probes and four different restriction enzymes were used for Southern blot analyses by the non-radioactive digoxigenin labeling technique. Alloplasmic regenerants showed a gain or loss of hybridization signals up to a high percentage, while euplasmic ones revealed only minor variability with respect to band stoichiometries. In 24 cases rearrangements in the mtDNA were proved. We suppose that recombination processes and selective amplification events are responsible for these findings.