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The distribution of fossil wood genera has been demonstrated to be an effective proxy for Mesozoic terrestrial climates. In this study, we investigated the phytocoenoses, which were associated with Xenoxylon confirmed to be a marker for a cool and/or wet climate in a boreal hemisphere (i.e., Xenoxylon-phytocoenoses) during the Mesozoic, using specimens of fossil wood. It was confirmed that Xenoxylon co-occurs more often with some wood genera than with others. For example, Protocedroxylon, a wood that is most likely related to the Pinaceae, is the genus most often associated with Xenoxylon-phytocoenoses. Although Taxodioxylon is also found in Xenoxylon-phytocoenoses, it is not found, however, as consistently as Protocedroxylon. The distribution and diversity of Xenoxylon-phytocoenoses changed throughout the Mesozoic. During the Late Triassic and Late Cretaceous, Xenoxylon-phytocoenoses had low diversity and were restricted to higher palaeolatitudes during the Late Cretaceous. However, during the Early to Middle Jurassic, Xenoxylon- phytocoenoses were distributed much farther south, while their diversity concomitantly increased sharply. From the Late Jurassic to the Early Cretaceous, the distribution of Xenoxylon-phytocoenoses moved northward in Europe and even more so in East Asia. The changes in the distribution of Xenoxylon-phytocoenoses are in agreement with changes in both global and regional climates. Our results also demonstrated that, within the Xenoxylon distribution range, the corresponding phytocoenoses were differentiated along a latitudinal gradient and according to the global climate change patterns during the Mesozoic.
The change in environmental parameters affects normal growth of plants, eventually reduces agricultural production. Ethylene plays vital roles in plant stress responses, germination, fruit ripening, organ abscission, pathogen response, and senescence. Expression of an ethylene-responsive transcription factor (ERF) was induced in Korean halophyte, Raphanus sativus var. hortensis f. raphanistroides (wild radish) by 200-mM sodium chloride (NaCl). Raphanus sativus ethylene-responsive transcription factor 1 (RsERF1) is also localized to nucleus, similar to other transcription factors. In yeast, RsERF1 showed transcriptional activation property, by expressing the reporter gene. Being a TF, RsERF1 specifically bound to the cisacting elements, GCC box and DRE/CRT in vitro, to initiate transcription. Homozygous T3 transgenic Arabidopsis, overexpressing RsERF1, showed significant tolerance against salt stress in soil-grown conditions. The tolerance was also marked by an increased germination rate of RsERF1 transgenics in salt-containing media. In RsERF1 overexpression lines, abiotic stress-related genes such as ABF3, ABF4, ADH, Rab18, and SUS1 were upregulated by 200-mM NaCl. ERFs have been studied and proven for their tolerance potential against various abiotic stresses, but RsERF1 belongs to an ERF subgroup called ethylene-responsive transcription factor related to AP2 (ERF-RAP2). Thus, this is a first report for ERF-RAP2 from Korean halophyte cDNA library. We believe that extensive posttranslational modification studies will reveal the role and location of RsERF1 in stress tolerance pathway.
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