The Crambe abyssinica plastome: Brassicaceae phylogenomic analysis, evolution of RNA editing sites, hotspot and microsatellite characterization of the tribe Brassiceae.

Crambe abyssinica is an important oilseed crop that accumulates high levels of erucic acid, which is being recognized as a potential oil platform for several industrial purposes. It belongs to the family Brassicaceae, assigned within the tribe Brassiceae. Both family and tribe have been the subject of several phylogenetic studies, but the relationship between some lineages and genera remains unclear. Here, we report the complete sequencing and characterization of the C. abyssinica plastome. Plastome structure, gene order, and gene content of C. abyssinica are similar to other species of the family Brassicaceae. The only exception is the rps16 gene, which is absent in many genera within the family Brassicaceae, but seems to be functional in the tribe Brassiceae, including C. abyssinica. However, the analysis of gene divergence shows that the rps16 is the most divergent gene in C. abyssinica and within the tribe Brassiceae. In addition, species of the tribe Brassiceae also show similar SSR loci distribution, with some regions containing a high number of SSRs, which are located mainly at the single copy regions. Six hotspots of nucleotide divergence among Brassiceae species were located in the single copy regions by sliding window analysis. Brassicaceae phylogenomic analysis, based on the complete plastomes of 72 taxa, resulted in a well-supported and well-resolved tree. The genus Crambe is positioned within the Brassiceae clade together with the genera Brassica, Raphanus, Sinapis, Cakile, Orychophragmus and Sinalliaria. Moreover, we report several losses and gains of RNA editing sites that occurred in plastomes of Brassiceae species during evolution.

Genetic stability of micropropagated plants of Crambe abyssinica Hochst using ISSR markers.

Crambe (Crambe abyssinica) is a non-edible annual herb, which was first cultivated to extract oil for industry, and now has great potential for biodiesel production. The objective of this investigation was to evaluate the genetic stability of micropropagated plants of the C. abyssinica Hochst cultivar 'FMS brilhante' using polymerase chain reaction techniques based on inter-simple sequence repeat (ISSR) molecular markers. The aim was to develop a protocol for the in vitro regeneration of these plants with low genetic variation as compared to the donor plant. For micropropagation, shoot tips from in vitro germinated seedlings were used as explants and were initially cultivated for 90 days on MS medium with 5.0 µM 6-benzylaminopurine (BAP), which at 90 days, led to the highest number of shoots per explant (NSE) (12.20 shoots) being detected. After 120 days, the interaction between BAP concentration and naphthalene acetic acid (NAA) was tested, and the highest NSE was observed following exposure to 0.0/0.5 µM BAP/NAA (11.40 shoots) and 1.0/0.0 µM BAP/NAA (11.00 shoots). The highest proportion of rooting phase were observed following exposure to 0.5 µM NAA (30%). The 13 ISSR primers used to analyze genetic stability produced 91 amplification products, of which only eight bands were polymorphic and 83 were monomorphic for all 10 regenerated crambe plants, compared to the donor plant explant. These results indicate that crambe shoot tips are a highly reliable explant that can be used to micropropagate genetically true-to-type plants or to maintain genetic stability, as verified using ISSR markers.

Production and genetic characterization of interspecific hybrids among Crambe abyssinica, Crambe hispanica and Crambe kralikii.

In this paper, interspecific crosses among Crambe abyssinica, Crambe hispanica, and Crambe kralikii were reported. In the C. hispanica x C. abyssinica (H x A) cross, 118 F1 hybrids were produced without embryo rescue, while 5 F1 hybrids were obtained with embryo rescue, when C. hispanica was used as the female parent. In the reciprocal cross (A x H), 232 hybrids were obtained without embryo rescue. From more than 1000 C. kralikii flowers pollinated with pollen grains of C. abyssinica (K x A), only 2 F1 hybrids were obtained with embryo rescue, whereas the reciprocal cross produced no hybrids, even with embryo rescue. The hybrids were confirmed at the morphological, cytological, and molecular levels. In the combinations of A x H and H x A, many BC1 hybrids were obtained without embryo rescue. In contrast, in the K x A cross, only 7 BC1 plants were obtained with embryo rescue, while no seed set was achieved under self-pollination or in backcrosses without embryo rescue. In the H x A F1 hybrids, the pollen stainability was 65.4-86.0%, with an average of 76.9%. In comparison, the pollen viability of hybrids in the reciprocal cross (A x H) ranged from 66.2 to 81.1%, with an average of 75.4%. Fertile pollen grains were not found in the K x A F1 hybrids. All F1 hybrids of the 3 crosses (H x A, A x H, and K x A) had the expected 2n = 75 chromosomes. AFLP analyses indicated that all F1 hybrids and their progenies had typical bands of the parents. These hybrids and progenies are anticipated to be valuable for future C. abyssinica improvement in breeding programs.