Abstract Detail

Functional Genetics/Genomics

Broz, Amanda [1], Keene, Lexi [1], Hodus, Mychaela [1], Sloan, Daniel [1].

Heteroplasmy and the dynamics of cytoplasmic DNA transmission.

The inheritance of mitochondrial and plastid DNA is commonly considered to be uniparental, allowing for little or no variation in organelle genome sequence.   However, recent evidence suggests that heteroplasmy, the presence of more than one type of mitochondrial or plastid genome in an individual, is more common than previously thought.   In some cases, heteroplasmy is associated with paternal leakage of organellar DNA, but the presence of two or more genome variants can also arise from  de novo  mutation.   Regardless of the source, the extent to which heteroplasmies are vertically transmitted across generations or eliminated through successive bottlenecking is not well understood in plants.   We previously identified a specific genetic background of Arabidopsis thaliana that exhibits increased organelle mutation rates, resulting in detectable levels of heteroplasmy.   Here, we used ddPCR to quantitatively track the distribution and inheritance of heteroplasmies associated with  de novo  single nucleotide variants (SNV) in both mitochondria and plastid genomes.  Patterns of SNV inheritance revealed striking differences between the two organelles.   In progeny of heteroplasmic mothers, we found that plastid SNVs rapidly reached fixation or went extinct, whereas mitochondrial heteroplasmies were retained over generations.   Within individual plants, we found that rates of plastid heteroplasmy varied substantially within an individual, indicative of vegetative segregation.   Conversely, rates of mitochondrial heteroplasmy were relatively stable between tissues and throughout development.   Our results suggest that the genetic bottlenecks associated with organelle DNA transmission both within and across generations are tighter in plastids than mitochondria, leading to the rapid loss of heteroplasmy in plastids.  One explanation for the highly polarized distribution associated with plastid SNV inheritance is that each plastid contains a single genotype, and the unit of segregation is the organelle.   In contrast, patterns of mitochondrial SNV inheritance suggest that more than one type of genome is retained within a single mitochondrion, and the unit of segregation is the mitochondrial genome.   These patterns likely reflect differences in organelle dynamics, as plastids undergo little inter-organelle genetic exchange, while mitochondria participate in fusion events that facilitate homologous recombination between genome copies.   To our knowledge, this study is the first to quantitatively assess the transmission dynamics of heteroplasmic variants arising from de novo mutation and their associated patterns of inheritance.   Our findings highlight how differences in organelle genome dynamics can have a massive impact on the fate of  de novo  mutations that arise in plastid and mitochondrial genomes.

1 - Colorado State University, 1878 Campus Delivery, Biology Department, Fort Collins, CO, 80523, United States

Keywords:
heteroplasmy
mitochondria
Plastid
uniparental inheritance
organelle
Bottleneck
vegetative segregation
mitochondrial genome.

Presentation Type: Poster
Session: P2, Functional Genetics and Genomics Posters
Location: Virtual/Virtual
Date: Tuesday, July 20th, 2021
Time: 5:00 PM(EDT)
Number: P2CG001
Abstract ID:295
Candidate for Awards:None