SUMMARY Retrograde plastid-to-nucleus signaling tightly controls and coordinates nuclear and plastid gene expression that is required for plastid biogenesis and chloroplast activities. As chloroplasts act as sensors of environmental changes, plastid-derived signaling also modulates stress responses of plants by transferring stress-related signals and altering nuclear gene expression. Various mutant screens have been undertaken to identify constituents of plastid signaling pathways. Almost all mutations identified in these screens have in common that they target plastid-specific but not extra-plastidic functions. They have been suggested to define either genuine constituents of retrograde signaling pathways or components required for the synthesis of plastid signals. Here we report the characterization of the caa33 (constitutive activator of AAA-ATPase) mutant, which reveals another way of how mutations that affect plastid functions may modulate retrograde plastid signaling. caa33 disturbs a plastid-specific function by impeding plastid division thereby perturbing plastid homeostasis. This results in pre-conditioning plants by activating the expression of stress genes, enhancing pathogen resistance and attenuating the plant’s capacity to respond to plastid signals. Our study reveals an intimate link between chloroplast activity and the plant’s susceptibility to stress and emphasizes the need to consider the possible impact of pre-conditioning on retrograde plastid-to-nucleus signaling.

Fatty acids and their composition in seeds determine oil value for nutritional or industrial purposes and also affect seed germination as well as seedling establishment. To better understand the genetic basis of seed fatty acid biosynthesis in oilseed rape (Brassica napus L.) we applied a genome-wide association study, using 91,205 single nucleotide polymorphisms (SNPs) characterized across a mapping population with high-resolution skim genotyping by sequencing (SkimGBS). We identified a cluster of loci on chromosome A05 associated with oleic and linoleic seed fatty acids. The delineated genomic region contained orthologs of the Arabidopsis thaliana genes known to play a role in regulation of seed fatty acid biosynthesis such as Fatty acyl-ACP thioesterase B (FATB) and Fatty Acid Desaturase (FAD5). This approach allowed us to identify potential functional genes regulating fatty acid composition in this important oil producing crop and demonstrates that this approach can be used as a powerful tool for dissecting complex traits for B. napus improvement programs.

The world-wide demand for additional protein sources for human nutrition and animal feed keeps rising due to rapidly growing world population. Oilseed rape is a second important oil producing crop and the by-product of the oil production is a protein rich meal. The protein in rapeseed meal finds its application in animal feed and various industrial purposes, but its improvement is of great interest, especially for non-ruminants and poultry feed. To be able to manipulate the quality and quantity of seed protein in oilseed rape, understanding genetic architecture of seed storage protein (SSPs) synthesis and accumulation in this crop species is of great interest. For this, application of modern molecular breeding tools such as whole genome sequencing, genotyping, association mapping, and genome editing methods implemented in oilseed rape seed protein improvement would be of great interest. This review examines current knowledge and opportunities to manipulate of SSPs in oilseed rape to improve its quality, quantity and digestibility.

Two mutants of winter rapeseed (Brassica napus L. var. oleifera) with an increased amount of oleic acid in seeds were created by chemical mutagenesis (HOR3-M10453 and HOR4-M10464). The overall performance of the mutated plants was much lower than that of wild-type cultivars. Multiple rounds of crossing with high-yielding double-low (“00”) cultivars and breeding lines having valuable agronomic traits, followed by selection of high oleic acid genotypes is then needed to obtain new “00” varieties of rapeseed having high oleic acid content in seeds. To perform such selection, the specific codominant cleaved amplified polymorphic sequences (CAPS) marker was used. This marker was designed to detect the presence of two relevant point mutations in the desaturase gene BnaA.FAD2, and it was previously described and patented. The specific polymerase chain reaction product (732 bp) was digested using FspBI restriction enzyme that recognizes the 5′-C↓TAG-3′ sequence which is common to both mutated alleles, thereby yielding band patterns specific for those alleles. The method proposed in the patent was redesigned, adjusted to specific laboratory conditions, and thoroughly tested. Different DNA extraction protocols were tested to optimize the procedure. Two variants of the CAPS method (with and without purification of amplified product) were considered to choose the best option. In addition, the ability of the studied marker to detect heterozygosity in the BnaA.FAD2 locus was also tested. Finally, we also presented some examples for the use of the new CAPS marker in the marker-assisted selection (MAS) during our breeding programs. The standard CTAB method of DNA extraction and the simplified, two-step (amplification/digestion) procedure for the CAPS marker are recommended. The marker was found to be useful for the detection of two mutated alleles of the studied BnaA.FAD2 desaturase gene and can potentially assure the breeders of the purity of their HOLL lines. However, it was also shown that it could not detect any other alleles or genes that were revealed to play a role in the regulation of oleic acid level.

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