The Meishan section, South China is the Global Stratotype Section and Point (GSSP) for the Permian-Triassic boundary (PTB), and also is well known for the best record demonstrating the Permian-Triassic mass extinction (PTME) all over the world. This section has also been studied using multidisciplinary approaches to reveal the possible causes for the greatest Phanerozoic biocrisis of life on Earth; many important scenarios interpreting the great dying have been proposed on the basis of data from Meishan. Nevertheless, debates on biotic extinction patterns and possible killers still continue. This paper reviews all fossil and sedimentary records from the Permo-Triassic (P-Tr) transition, based on previously published data and our newly obtained data from Meishan, and assesses ecologically the PTME and its aftermath to determine the biotic response to climatic and environmental extremes associated with the biocrisis. Eight updated conodont zones: C. yini, C. meishanensis, H. changxingensis, C. taylorae, H. parvus, I. staeschei, I. isarcica, and C. planate Zones are proposed for the PTB beds at Meishan.

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This is a repository copy of Biotic responses to volatile volcanism and environmental stresses over the Guadalupian-Lopingian (Permian) transition.

Transcription factors that include myeloblastosis (MYB), basic helix-loop-helix (bHLH), and tryptophan-aspartic acid (WD)-repeat protein often form a ternary complex to regulate the phenylpropanoid pathway. However, only a few MYB and bHLH members involved in the biosynthesis of salvianolic acid B (Sal B) have been reported, and little is known about Sal B pathway regulation by the WD40 protein transparent testa glabra 1 (TTG1)-dependent transcriptional complexes in Salvia miltiorrhiza. We isolated SmTTG1 from that species for detailed functional characterization. Enhanced or reduced expression of SmTTG1 was achieved by gain- or loss-of-function assays, respectively, revealing that SmTTG1 is necessary for Sal B biosynthesis. Interaction partners of the SmTTG1 protein were screened by yeast two-hybrid (Y2H) assays with the cDNA library of S. miltiorrhiza. A new R2R3-MYB transcription factor, SmMYB111, was found through this screening. Transgenic plants overexpressing or showing reduced expression of SmMYB111 upregulated or deregulated, respectively, the yields of Sal B. Both Y2H and bimolecular fluorescent complementation experiments demonstrated that SmMYB111 interacts with SmTTG1 and SmbHLH51, a positive regulator of the phenolic acid pathway. Our data verified the function of SmTTG1 and SmMYB111 in regulating phenolic acid biosynthesis in S. miltiorrhiza. Furthermore, ours is the first report of the potential ternary transcription complex SmTTG1-SmMYB111-SmbHLH51, which is involved in the production of Sal B in that species.

Real time quantitative PCR (RT-qPCR or qPCR) has been extensively applied for analyzing gene expression because of its accuracy, sensitivity, and high throughput. However, the unsuitable choice of reference gene(s) can lead to a misinterpretation of results. We evaluated the stability of 10 candidates – five traditional housekeeping genes (UBC21, GAPC2, EF-1α4, UBQ10, and UBC10) and five novel genes (SAND1, FBOX, PTB1, ARP, and Expressed1) – using the transcriptome data of Gentiana macrophylla. Common statistical algorithms ΔCt, GeNorm, NormFinder, and BestKeeper were run with samples collected from plants under various experimental conditions. For normalizing expression levels from tissues at different developmental stages, GAPC2 and UBC21 had the highest rankings. Both SAND1 and GAPC2 proved to be the optimal reference genes for roots from plants exposed to abiotic stresses while EF-1α4 and SAND1 were optimal when examining expression data from the leaves of stressed plants. Based on a comprehensive ranking of stability under different experimental conditions, we recommend that SAND1 and EF-1α4 are the most suitable overall. In this study, to find a suitable reference gene and its real-time PCR assay for G. macrophylla DNA content quantification, we evaluated three target genes including WRKY30, G10H, and SLS, through qualitative and absolute quantitative PCR with leaves under elicitors stressed experimental conditions. Arbitrary use of reference genes without previous evaluation can lead to a misinterpretation of the data. Our results will benefit future research on the expression of genes related to secoiridoid biosynthesis in this species under different experimental conditions.

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