bims-plasge Biomed News
on Plastid genes
Issue of 2020‒08‒23
four papers selected by
Vera S. Bogdanova
Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences

  1. Plant J. 2020 Aug 17.
      Spontaneous mutants are mainly obtained from tissue culture or natural occurrence in plants. The traditional strategy to identify spontaneously mutated genes is to continuously backcross these mutants to another variety and develop a near-isogenic F2 population for map-based cloning or bulked segregant analysis (BSA). However, this strategy is time-consuming. Here, we have developed a new method to efficiently accelerate the identification process. The chemical mutagen ethyl methanesulfonate (EMS) was first used to treat the wild-type of the spontaneous mutants to induce thousands of neutral mutations. An induced individual without any statistically significant phenotypic changes which was compared with the wild-type was chosen as the neutral mutant. The spontaneous mutant was then crossed with the neutral mutant to develop a pseudo-near-isogenic F2 population in which only the induced neutral mutations and the causal mutation were segregated in the genome. This population ensures that the variation of the mutated trait is controlled only by the spontaneously mutated gene. Finally, after by sequencing the neutral mutant and the mutant type DNA pool of the F2 population, the spontaneous mutation will be identified quickly by bioinformatics analysis. Using this method, two spontaneously mutated genes were identified successfully. Therefore, the neutral mutant-bridging (NMB) method efficiently identifies spontaneously mutated genes in rice, and its value in other plants is discussed.
    Keywords:  Spontaneous mutation; bulked segregant analysis; causal mutation; neutral mutant; pseudo-near-isogenic F2 population
  2. Plant Cell Physiol. 2020 Aug 20. pii: pcaa110. [Epub ahead of print]
      Pentatricopeptide repeat (PPR) proteins involved in mitochondrial RNA cytidines (C) to uridines (U) editing mostly result in the stagnant embryo and endosperm development when losing function. However, less is known about PPR that involved in farinaceous endosperm formation and maize quality. Here, we cloned a maize DYW-type PPR Defective Kernel605 (Dek605). Mutation of Dek605 delayed seed and seedling development. Mitochondrial transcript analysis of dek605 revealed that loss of DEK605 impaired C-to-U editing at the nad1-608 site and fails to alter Ser203 to Phe203 in NAD1 (dehydrogenase complex I), disrupting complex I assembly and reducing NADH dehydrogenase activity. Meanwhile, complex III and IV in the cytochrome pathway, as well as AOX2 in the alternative respiratory pathway, are dramatically increased. Interestingly, the mutation resulted in opaque endosperm and increased levels of the free amino acids ALA, ASP and PHE in dek605. The down- and up-regulated genes were mainly involving in stress response-related and seed dormancy-related pathways, respectively, were observed after transcriptome analysis of dek605 at 12 day after pollination (DAP). Collectively, these results indicate that Dek605 specifically affects the single nad1-608 site and is required for normal seed development and resulted in nutritional quality relevant amino acid accumulation.
    Keywords:   Dek605 ; RNA editing; mitochondria; pentatricopeptide repeat (PPR) protein; quality improvement; seed development
  3. Proc Natl Acad Sci U S A. 2020 Aug 19. pii: 202004405. [Epub ahead of print]
      Plastids, the defining organelles of plant cells, undergo physiological and morphological changes to fulfill distinct biological functions. In particular, the differentiation of chloroplasts into chromoplasts results in an enhanced storage capacity for carotenoids with industrial and nutritional value such as beta-carotene (provitamin A). Here, we show that synthetically inducing a burst in the production of phytoene, the first committed intermediate of the carotenoid pathway, elicits an artificial chloroplast-to-chromoplast differentiation in leaves. Phytoene overproduction initially interferes with photosynthesis, acting as a metabolic threshold switch mechanism that weakens chloroplast identity. In a second stage, phytoene conversion into downstream carotenoids is required for the differentiation of chromoplasts, a process that involves a concurrent reprogramming of nuclear gene expression and plastid morphology for improved carotenoid storage. We hence demonstrate that loss of photosynthetic competence and enhanced production of carotenoids are not just consequences but requirements for chloroplasts to differentiate into chromoplasts.
    Keywords:  carotenoid; chromoplast; differentiation; phytoene; synthetic
  4. Plant Direct. 2020 Aug;4(8): e00257
      Seed abortion and ovary abscission, two types of postzygotic reproductive barriers, are often observed in interspecific and/or interploidy crosses in plants. However, the mechanisms underlying these reproductive barriers remain unclear. Here, we show that the distinct types of seed developmental abnormalities (type I and type II seed abortion) occur in a phased manner as maternal to paternal genome dosage increases and that type II seed abortion is followed by ovary abscission. We revealed that these two types of seed developmental abnormalities are observed during seed development in the interploidy-interspecific crosses of Nicotiana suaveolens and N. tabacum. Moreover, in the cross showing type II seed abortion, several events, such as changes in abscission-related gene expression and lignin deposition, occurred in the ovary abscission zone, eventually leading to ovary abscission. Notably, successive increases in maternal ploidy using ploidy manipulated lines resulted in successive type I and type II seed abortions, and the latter was accompanied by ovary abscission. Conversely, both types of seed abortion and ovary abscission could be overcome with a ploidy manipulation technique that balances parental ploidy levels. We thus concluded that a high maternal genome excess cross may cause severe seed developmental defects and ovary abscission. Based on our findings, we propose a model explaining the abortion phenomena, where an interaction between the promotive and inhibitive effects of the parental genomes determines the developmental destiny of seeds.Significance statement: We demonstrate that a stepwise increase in maternal ploidy results in a stepwise increase in seed abortion severity, leading to ovary abscission in plants. We propose a model explaining the abortion phenomena, where an interaction between the promotive and inhibitive effects of the parental genomes determines the developmental destiny of seeds.
    Keywords:  Nicotiana; effective ploidy; interploidy cross; interspecific cross; ovary abscission; seed abortion