The complete mitogenome assemblies of 10 diploid potato clones reveal recombination and overlapping variants.

The potato mitogenome is complex and to understand various biological functions and nuclear-cytoplasmic interactions, it is important to characterize its gene content and structure. In this study, the complete mitogenome sequences of nine diploid potato clones along with a diploid Solanum okadae clone were characterized. Each mitogenome was assembled and annotated from Pacific Biosciences (PacBio) long reads and 10X genomics short reads. The results show that each mitogenome consists of multiple circular molecules with similar structure and gene organization, though two groups (clones 07506-01, DW84-1457, 08675-21 and H412-1 in one group, and clones W5281-2, 12625-02, 12120-03 and 11379-03 in another group) could be distinguished, and two mitogenomes (clone 10908-06 and OKA15) were not consistent with those or with each other. Significant differences in the repeat structure of the 10 mitogenomes were found, as was recombination events leading to multiple sub-genomic circles. Comparison between individual molecules revealed a translocation of ∼774 bp region located between a short repeat of 40 bp in molecule 3 of each mitogenome, and an insertion of the same in molecule 2 of the 10908-06 mitogenome. Finally, phylogenetic analyses revealed a close relationship between the mitogenomes of these clones and previously published potato mitogenomes.

The complete plastome sequences of nine diploid potato clones.

Potato (Solanum tuberosum L.) is the world's fourth most important food crop and essential for global food security. The potato chloroplast genomes, the plastomes, are highly conserved and are largely studied for their maternal lineages. In this study, we assembled the complete circular plastome sequences of nine diploid potato clones, with sizes ranging between 155,296 bp and 155,564 bp. Annotation of these plastomes reveals that they each have 141 genes in a similar order. The computational chloroplast DNA typing reveals three plastid DNA types among the nine plastomes and they are grouped according to these types in the phylogeny.

Tuber transcriptome profiling of eight potato cultivars with different cold-induced sweetening responses to cold storage.

Tubers are vegetative reproduction organs formed from underground extensions of the plant stem. Potato tubers are harvested and stored for months. Storage under cold temperatures of 2-4 °C is advantageous for supressing sprouting and diseases. However, development of reducing sugars can occur with cold storage through a process called cold-induced sweetening (CIS). CIS is undesirable as it leads to darkened color with fry processing. The purpose of the current study was to find differences in biological responses in eight cultivars with variation in CIS resistance. Transcriptome sequencing was done on tubers before and after cold storage and three approaches were taken for gene expression analysis: 1. Gene expression correlated with end-point glucose after cold storage, 2. Gene expression correlated with increased glucose after cold storage (after-before), and 3. Differential gene expression before and after cold storage. Cultivars with high CIS resistance (low glucose after cold) were found to increase expression of an invertase inhibitor gene and genes involved in DNA replication and repair after cold storage. The cultivars with low CIS resistance (high glucose after cold) showed increased expression of genes involved in abiotic stress response, gene expression, protein turnover and the mitochondria. There was a small number of genes with similar expression patterns for all cultivars including genes involved in cell wall strengthening and phospholipases. It is proposed that the pattern of gene expression is related to chilling-induced DNA damage repair and cold acclimation and that genetic variation in these processes are related to CIS.

Verticillium dahliae Disease Resistance and the Regulatory Pathway for Maturity and Tuberization in Potato.

Kleb. is a pathogenic fungus causing wilting, chlorosis, and early dying in potato ( L.). Genetic mapping of resistance to was done using a diploid population of potato. The major quantitative trait locus (QTL) for resistance was found on chromosome 5. The gene, controlling earliness of maturity and tuberization, was mapped within the interval. Another QTL on chromosome 9 co-localized with the wilt resistance gene marker. Epistasis analysis indicated that the loci on chromosomes 5 and 9 had a highly significant interaction, and that functioned downstream of The alleles were sequenced and found to encode StCDF1.1 and StCDF1.3. Interaction between the resistance allele and the was demonstrated, but not for Genome-wide expression QTL (eQTL) analysis was performed and genes with eQTL at the and loci were both found to have similar functions involving the chloroplast, including photosynthesis, which declines in both maturity and wilt. Among the gene ontology (GO) terms that were specific to genes with eQTL at the , but not the locus, were those associated with fungal defense. These results suggest that controls fungal defense and reduces early dying in wilt through affecting genetic pathway controlling tuberization timing.

Pathogen and Pest Responses Are Altered Due to RNAi-Mediated Knockdown of GLYCOALKALOID METABOLISM 4 in Solanum tuberosum.

Steroidal glycoalkaloids (SGAs) are major secondary metabolites constitutively produced in cultivated potato Solanum tuberosum, and α-solanine and α-chaconine are the most abundant SGAs. SGAs are toxic to humans at high levels but their role in plant protection against pests and pathogens is yet to be established. In this study, levels of SGAs in potato were reduced by RNA interference (RNAi)-mediated silencing of GLYCOALKALOID METABOLISM 4 (GAME4)-a gene encoding cytochrome P450, involved in an oxidation step in the conversion of cholesterol to SGA aglycones. Two GAME4 RNAi lines, T8 and T9, were used to investigate the effects of manipulation of the SGA biosynthetic pathway in potato. Growth and development of an insect pest, Colorado potato beetle (CPB), were affected in these lines. While no effect on CPB leaf consumption or weight gain was observed, early instar larval death and accelerated development of the insect was found while feeding on leaves of GAME4 RNAi lines. Modulation of SGA biosynthetic pathway in GAME4 RNAi plants was associated with a larger alteration to the metabolite profile, including increased levels of one or both the steroidal saponins or phytoecdysteroids, which could affect insect mortality as well as development time. Colonization by Verticillium dahliae on GAME4 RNAi plants was also tested. There were increased pathogen levels in the T8 GAME4 RNAi line but not in the T9. Metabolite differences between T8 and T9 were found and may have contributed to differences in V. dahliae infection. Drought responses created by osmotic stress were not affected by modulation of SGA biosynthetic pathway in potato.