Abstract
Mitochondrial markers can be used to differentiate diverse mitotypes as well as cytoplasms in angiosperms. In cauliflower, cultivation of hybrids is pivotal in remunerative agriculture and cytoplasmic male sterile lines constitute an important component of the hybrid breeding. In diversifying the source of male sterility, it is essential to appropriately differentiate among the available male sterile cytoplasms in cauliflower. PCR polymorphism at the key mitochondrial genes associated with male sterility will be instrumental in analyzing, molecular characterization, and development of mitotype-specific markers for differentiation of different cytoplasmic sources. Presence of auto- and alloplasmic cytonuclear combinations result in complex floral abnormalities. In this context, the present investigation highlighted the utility of organelle genome-based markers in distinguishing cytoplasm types in Indian cauliflowers and unveils the epistatic effects of the cytonuclear interactions influencing floral phenotypes. In PCR-based analysis using a set of primers targeted to orf-138, 76 Indian cauliflower lines depicted the presence of Ogura cytoplasm albeit the amplicons generated exhibited polymorphism within the ofr-138 sequence. The polymorphic fragments were found to be spanning over 200–280 bp and 410–470 bp genomic regions of BnTR4 and orf125, respectively. Sequence analysis revealed that such cytoplasmic genetic variations could be attributed to single nucleotide polymorphisms and insertion or deletions of 31/51 nucleotides. The cytoplasmic effects on varying nuclear-genetic backgrounds rendered an array of floral abnormalities like reduction in flower size, fused flowers, splitted style with the exposed ovule, absence of nonfunctional stamens, and petaloid stamens. These floral malformations caused dysplasia of flower structure affecting female fertility with inefficient nectar production. The finding provides an important reference to ameliorate understanding of mechanism of cytonuclear interactions in floral organ development in Brassicas. The study paves the way for unraveling developmental biology of CMS phenotypes in eukaryotic organisms and intergenomic conflict in plant speciation.
Highlights
Mitochondria play a central role in energy production by oxidative phosphorylation, apoptosis, and other cellular processes (Chen et al, 2017; Shu et al, 2018)
The amplification pattern of the gene-based primers indicated that the cytoplasm type of all the cytoplasmic male sterility (CMS) lines in Indian cauliflower was derived from Ogura cytoplasm; there was a variation at nucleotide level among the large genetic stock of Indian cauliflower
These results indicated presence of only Ogura cytoplasm in all the cauliflower lines and F1 hybrids under study, and none of the CMS lines and F1 hybrids were based on other types of cytoplasmic systems
Summary
Mitochondria play a central role in energy production by oxidative phosphorylation, apoptosis, and other cellular processes (Chen et al, 2017; Shu et al, 2018). The plant mitogenomes have the remarkable features of presence of highly diverse intergenetic regions, frequent mt-DNA rearrangements, slow evolution in mt-DNA sequences, and rapid structural evolution (Sloan, 2013; Chen et al, 2017) Attributed to these characteristics, the extensive genome reorganization and shuffling in gene order may occur in plant mitogenomes and unusual open reading frames (ORFs) are generated, some of which causes extreme phenotypes such as cytoplasmic male sterility (CMS) (Tanaka et al, 2012; Chen et al, 2017; Singh et al, 2019a). CMS is an important trait to provide new insights into plant nucleo-mitochondrial communication
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