Chloroplasts can finally hope to have sex

A billion years of abstinence: Chloroplasts can finally hope to have sex 0.05, ***P< 0.001. Only the cryogenic treatment had a significant effect (P = 1.22 × 10 −101). Values ​​represent log fold changes of 10. Means for each treatment are shown in black horizontal lines, with CI95 in colored boxes. e, RFLP analysis of selected PPI lines: HL1, high illumination; H1, D6 heat: dehydration. C111, C116, C200, chilling. RFLP analysis using EcoRV and XhoI (see panel b) yields fragments of 4.7 kb for the parental plastids and 3.2 kb for the maternal (WT) plastids. The blot is representative of three independent experiments. f, Localization of GFP fluorescence to the chloroplast. GFP fluorescence and an overlay with Chl fluorescence of WT, WT transplastomic WT ptGFP and PPI line are shown. Images are representative of hundreds of independent PPI lines analyzed. Scale bar, 10 µm. Credit: Plants of Nature (2023). DOI: 10.1038 / s41477-022-01323-7" width="800" height="530"/>

Identification of abiotic factors that control plastid inheritance. aA genetic screen of paternal plastid transmission. (I) at the beginning of flowering, transplastomic plants (WTptGFP) to abiotic stress so that the male gametophyte develops under stress. (Second) Greenhouse-grown plants with wild-type plastids are fertilized with pollen from stressed WTptGFP the plants. (Third) seeds were sown on medium containing spectinomycin. Seedlings that have inherited their paternal plastids display green (spectinomycin-resistant) sectors. BPhysical maps of the maternal (wild-type, WT) and paternal (transplastomic, ptGFP) plastid genomes. The paternal plastid genome harbors modified genes: come back (resistance sign) f gfp (Reporter). Promoters, terminations (both blue) and relevant restriction sites are shown. The black bar depicts a hybridization probe for the RFLP. cTranslocation of the paternal plastid was detected by spectinomycin selection. Top left: Arrowheads indicate seedlings with green sectors. Top right: enlarged image of a green sector. Bottom: seedlings with green sectors displaying both fluorophore (left) and chlorophyll (chlorophyll, right). Scale bar, 1 mm. Dr, paternal transmission rates under stress. Circles represent the proportions of seedlings bearing GFP-positive green sectors per harvest (transcriptome, see Methods); circles in x Axis means that the parental transition was not found. Transmission rates of stressed and untreated plants, which are representative of Experiment 1, were compared. treatment effects (β(estimated using Model 1)nrep. total= 16 crops, ~4.35 million seedlings; extended data tables 1 and 2) and tested by a two-tailed parent simultaneously z– the exams. α = 0.05; NS, s >0.05, ***s<0.001. Only cryotherapy has a significant effect (s = 1.22 x 10−101). βValues ​​represent fold changes in the log10. Means for each treatment are shown in black horizontal lines, with CI95 in colored boxes. H, RFLP analysis of selected PPI lines: HL1, high luminance; H1, D6 heat: dehydration. C111, C116, C200, chilling. RFLP analysis using EcoRV and XhoI (see panel B) yields fragments of 4.7 kb for the paternal plastids and 3.2 kb for the maternal plastids. The blot is representative of three independent experiments. F, Localization of GFP fluorescence to the chloroplast. GFP fluorescence and overlay with Chl fluorescence of WT, transplastomic WT is shownptGFP and PPI line. Images are representative of hundreds of independent PPI lines analyzed. Scale bar, 10 µm. credit: Nature plants(2023). DOI: 10.1038/s41477-022-01323-7

Scientists at the Max Planck Institute for Molecular Plant Physiology in Potsdam (Germany) analyzed the inheritance of chloroplasts under different environmental conditions in nearly 4 million tobacco plants.

Contrary to the prevailing opinion that chloroplasts are only passed through mother plantchloroplasts can also be passed from parent to offspring under cold conditions, increasing the possibility of exchanging parental chloroplasts Genetic material With some. The new findings will facilitate the targeted use of chloroplast-encoded traits in plant breeding, and open new avenues for evolutionary research. The study has been published in Nature plants.

The story of flowers and bees is the classic introduction to a topic still rarely discussed in our society: sex in plants. When plants reproduce, sperms fuse inside pollen grains with Egg Inside the flower on which the pollen has landed. In this way, the genetic material of the cell nucleus of both parents is incorporated into the seed. This is important, as it allows the removal of harmful mutations that may accumulate in genetic material over generations.

Chloroplasts have their own genetic material

In addition to the genetic material in the cell nucleus, mitochondria and chloroplasts also contain genetic material. Mitochondria are the engines of cell combustion. Animal and plant cells use them to burn carbohydrates and utilize the released energy for metabolism. Plants also contain chloroplasts. They contain the green pigment chlorophyll, which is the solar power plants of cells. Chloroplasts allow plants to aggregate Solar energy in a process known as photosynthesis to produce carbohydrates.

Mitochondria and chloroplasts have their own genetic material, as they originate from bacteria that were eaten by the ancestors of modern animal and plant cells over a billion years ago. Mitochondria and chloroplasts have created a symbiotic community within the cell, and former roommates are now indispensable to plant survival.

It is known that the genomes of mitochondria and chloroplasts, in contrast to the genetic material of V cell nucleusThey do not inherit equally from father and mother. Both are transmitted almost exclusively by the mother, either because they either do not enter the sperm at all, or their genetic material is dissolved in pollen. If the mitochondria and chloroplasts of the mother and father did not meet, they could not have sex to exchange genetic material. Therefore, deleterious genetic mutations must accumulate over generations and eventually lead to genome collapse.

Scientists have evaluated nearly 4 million plants

Scientists at the Max Planck Institute for Plant Molecular Physiology have discovered that, contrary to popular belief, tobacco plants It can pass routinely to the chloroplast of the parent plant under certain conditions Environmental conditions. The researchers first created ab plants that contained antibiotic-resistant chloroplasts. These plants were then exposed to different environmental conditions such as heat, cold, drought and strong light during pollen maturation.

Pollen from these plants was used to pollinate unmodified parent plants. Seeds produced from this cross were grown in culture medium containing the appropriate antibiotic. Since only chloroplasts survive on this medium, cells containing chloroplasts from the parent plant appear green, while plants containing only chloroplasts inherited from the mothers are pale, as these chloroplasts fade due to their sensitivity to antibiotics .

Due to the scarcity of paternally inherited chloroplasts, the scientists had to look at nearly 4 million seedlings to prove that the proportion of paternally inherited chloroplasts was 150 times higher under cold treatment than under normal temperature. says Stephanie Roof, one of the study’s authors.

Chloroplast genetics can be manipulated

After this initial success, the researchers delved into the details: “We know that cold slows the activity of enzymes. We therefore suspect that an enzyme may be involved in blocking chloroplast paternal inheritance,” commented Enrique Gonzalez-Durán, who was also involved in the study. The scientists selectively bred plants with a defective enzyme that normally breaks down the genetic material of chloroplasts during pollen maturation.

Plants with a defective enzyme also showed a significant increase in paternal inheritance of chloroplasts. When combining the enzyme defect with cold application during pollen development resulted in a paternal inheritance rate of 2–3%. “This may not sound like much, but it’s huge compared to the 1 in 100,000 chance of this happening under normal conditions. It will be very interesting to see if the chloroplasts inherited from the mother and father actually exchange genetic material with each other,” says Ken Pan Chung. , another author of the study.

The discovery that the heritability of chloroplasts can be controlled by temperature and changes in individual enzymes in a plant opens up entirely new possibilities for plant breeding.

“Because it was previously thought that mitochondria and chloroplasts were always inherited together and only from the mother, there was no way to pass on the traits encoded in their genetic material separately. The possibility of chloroplasts also being passed on from the father by placing plants in the cold could open the door to breeding programs. completely new,” explains Ralf Bock, head of the research group.

Why mitochondria; And Chloroplasts It is largely inherited from the mother is still not clear. The fact that this type of inheritance can respond so flexibly to environmental conditions is likely to lead evolutionary biologists to rethink some of their current theories and models. “This also shows how important it is to consider environmental conditions in genetic research. Chloroplasts led us to believe for decades that they lived sexually abstinent, but now we can’t be sure anymore,” says Bock.

more information:
Ralph Bok, Control of plastid inheritance by environmental and genetic factors, Nature plants(2023). DOI: 10.1038/s41477-022-01323-7.

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