bims-plasge Biomed News
on Plastid Genes
Issue of 2018‒07‒01
four papers selected by
Vera S. Bogdanova
Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences

  1. Gene. 2018 Jun 20. pii: S0378-1119(18)30721-2. [Epub ahead of print]
      Myelocytomatosis (MYC) transcription factors (TFs) are key regulators of the jasmonic acid (JA) signaling pathway. In cell cultures, methyl jasmonate (MeJA) can improve the production of taxol, which is a complex terpenoid compound with an intense antitumor activity. However, the functions of MYC genes in Taxus sp. (yew trees) remain poorly known. Based on Taxus sp. transcriptome changes induced by MeJA, a TcMYC gene was isolated in a previous study. Here, we further characterized the TcMYC TF encoded by that gene and four other yew MYC TFs previously obtained. Three yew MYC TFs had the typical basic helix-loop-helix (bHLH)-MYC_N region, but the other two MYC did not, although all five presented the bHLH domain. TcMYC was localized to the nuclei, and phylogenetic analysis indicated that the yew MYC TFs were closely related to Arabidopsis thaliana MYC1/2 and maize R protein. The yeast one-hybrid assay showed that TcMYC binds the G-box of the promoter of taxane 5α-hydroxylase. Transcript levels of TcMYC revealed that TcMYC was highly expressed in xylem and leaves, and up-regulated by drought and high-salinity stresses. Coronatine (COR) has recently been used as a new elicitor to improve the production of taxol in cell cultures; TcMYC was strongly expressed at 2 and 4 h after COR treatment, but decreased at 12 and 24 h. Overall, the results obtained here provide new insights into the potential regulatory roles of MYC TFs on taxol biosynthesis in yew trees.
    Keywords:  G-box; MYC; Taxol; Taxus sp.; Transcription factor; bHLH
  2. Mol Phylogenet Evol. 2018 Jun 21. pii: S1055-7903(17)30822-9. [Epub ahead of print]
      Phylogenetic relationships among the taxa of Crocus series Crocus are still unclear, preventing the understanding of species diversity and the evolution of the important spice saffron (Crocus sativus). Therefore, we analyzed sequences of two chloroplast (trnL-trnF, matK-trnK) and three nuclear (TOPO6, ribosomal DNA ETS and ITS) marker regions to infer phylogenetic relationships among all species belonging to series Crocus. Our phylogenetic analyses resolved the relationships among all taxa of the series. Crocus hadriaticus and the former C. pallasii subspecies appeared polyphyletic. The latter deserve elevating the subspecies to species rank, while for C. hadriaticus a detailed study of species boundaries is necessary. Multi-locus and also genome-wide single nucleotide polymorphism data obtained through genotyping-by-sequencing placed C. sativus within C. cartwrightianus with no indication that other Crocus species contributed to the evolution of the triploid. Our analyses thus made an autotriploid origin of C. sativus from C. cartwrightianus very likely.
    Keywords:  Crocus series Crocus; GBS; evolution; multi-locus analysis; phylogeny; saffron
  3. Biochem Biophys Res Commun. 2018 Jun 21. pii: S0006-291X(18)31420-7. [Epub ahead of print]
      Brassica campestris Male Fertility 20 (BcMF20) is a typical zinc-finger transcription factor that was previously isolated from flower buds of Chinese cabbage (Brassica campestris ssp. chinensis). By applying expression pattern analysis, it can be known that BcMF20 was specifically and strongly expressed in tapetum and pollen, beginning from the uninucleate stage, and was maintained during the mature-pollen stage. As BcMF20 was highly conserved in Cruciferae, it can be indicated that this zinc-finger transcription factor is important during the growth of Cruciferae. In this study, 12 C2H2-type zinc-finger TFs which shared high homology with BcMF20 were found from NCBI via BLAST. A new molecular phylogenetic tree was constructed by the comparison between BcMF20 and these 12 C2H2-type zinc-finger TFs with NJ method. By analyzing this phylogenetic tree, the evolution of BcMF20 was discussed. Then, antisense RNA technology was applied in the transgenesis of Arabidopsis thaliana to get the deletion mutants of BcMF20, so that its function during the pollen development can be identified. The results showed: BcMF20 are in the same clade with three genes from Arabidopsis. The inhibition of BcMF20 expression led to smaller amounts of and lower rate in germination of pollen and lower rate in fruit setting in certain transgenetic plants. This also led to the complete collapse of pollen grains. By SEM and TEM, pollen morphology and anther development processes were observed. In the middle uninucleate microspore stage, a relatively thin or even no primexine was formed in microspores. This may result in the malformation of the pollen wall and finally cause the deformity of pollens. Above all, it can be indicated that BcMF20 may act as a part of regulation mechanisms of TAZ1 and MS1. Together they play a role in a genetic pathway in the tapetum to act on proliferation of tapetal cells and keep the normal development of pollens.
    Keywords:  Brassica campestris ssp. chinensis; Pollen wall development; TFs; Tapetum; Vacuole
  4. Planta. 2018 Jun 23.
      MAIN CONCLUSION: Freezing resistance strategies vary in Arabidopsis depending on origin. Southern accessions may avoid or tolerate freezing, while northern ones are always tolerant and reduce the proportion of freezable tissue water during acclimation. Survival of sub-zero temperatures can be achieved by either avoiding or tolerating extracellular ice formation. Conflicting evidence has been presented showing that detached leaves of Arabidopsis thaliana are either freeze avoiding or tolerant. Here, we used three different natural Arabidopsis accessions from different habitats to investigate the frost resistance strategy of whole plants in soil. Plants were cooled to fixed temperatures or just held at their individual ice nucleation temperature for different time intervals. Tissue damage of whole plants was compared to the standard lethal temperature determined for detached leaves with external ice nucleation. While all detached leaves survived freezing when ice nucleation was externally initiated at mild sub-zero temperatures, whole plants of the southern accession behaved as freeze avoiding in the non-acclimated state. The northern accessions and all cold acclimated plants were freezing tolerant, but the duration of the freezing event affected tissue damage. Because this pointed to cell dehydration as mechanism of damage, the proportion of freezable water in leaves and osmolality of cell sap was determined. Indeed, the freezing tolerant accession Rsch had a lower proportion of freezable water and higher cell sap osmolality compared to the sensitive accession C24 in the cold acclimated state.
    Keywords:  Cold acclimation; Differential scanning calorimetry; Differential thermal analysis; Freeze avoidance; Freezing tolerance; Ice nucleation