Karrikins are active components of smoke that can promote seed germination and regulate seedling morphogenesis. However, the role of karrikins as alleviators of abiotic stress remains largely elusive. In this study, we examined whether exogenous application of karrikin1 (KAR1) might improve drought tolerance in creeping bentgrass (Agrostis stolonifera cv. PennA4), and investigated the underlying mechanism. We found that exogenous application of 100 nM KAR1 enhanced drought tolerance in creeping bentgrass, as manifested by significant increases in leaf relative water content, efficiency of photosystem II, leaf chlorophyll content, proline content, and membrane stability, as well as significantly enhanced activities of antioxidant enzymes. RT‒PCR analysis indicated that improved drought stress tolerance by application of KAR1 might be related to upregulation expression of karrikin-responsive genes (KAI2, MAX2 and AFL1), transcription factors (ABF3, bHLH148, MYB13 and DREB2A), antioxidant defense genes (Cu/Zn-SOD, APX2, CAT1, and POD2), and downregulation expression of chlorophyll-degradation genes (PPH and Chl-PRX). These findings suggest that KAR1 may promote the drought tolerance of creeping bentgrass by activating karrikin-responsive genes and transcription factors, enhancing proline accumulation and antioxidant capacity, and suppressing leaf senescence under prolonged drought stress.
Tsuga (hemlock) is a small genus of 10 extant species in the Pinaceae, with a disjunct distribution in East Asia and eastern and western North America. Reliable species‐level identification of Tsuga fossils depends on the discovery of seed cones with intact bracts, but such cones are rare in the fossil record. Here we describe a new fossil species of hemlock as T. weichangensis sp. nov. based on exquisitely preserved seed cones with nearly complete bracts from the Lower Miocene of Weichang, Hebei Province, North China. This fossil species displays a mosaic of characters between Tsuga and Nothotsuga. The well‐developed and slightly exserted bract scales of T. weichangensis are reminiscent of Nothotsuga, but other characters, such as nonleaved peduncles and tongue‐shaped bract scales, in addition to monosaccate pollen found at the same fossil locality, suggest an affinity closer to Tsuga. Cladistic analysis based on 15 morphological characters and a molecular backbone constraint supports the assignment of these fossil cones to Tsuga rather than Nothotsuga, and places the fossil species of T. weichangensis in an unresolved polytomy within the genus Tsuga. The occurrence of Tsuga seed cone fossils indicate the paleoclimate in the Miocene of Weichang was warmer and more humid than today's climate, which is consistent with the paleoclimate reconstructed by paleopalynology.
Hymenophyllaceae (filmy ferns), with ca. 430 species, are the most species-rich family of early diverging leptosporangiate ferns but have a poor fossil record dating back to the Late Triassic period. Traditionally, Hymenophyllaceae comprise two species-rich genera or clades: Hymenophyllum (hymenophylloids) and Trichomanes sensu lato (s.l.) (trichomanoids). Unequivocal fossils of Hymenophyllum have been reported from the Early Cretaceous of central Mongolia and the early Eocene of Okanogan Highlands, Washington, USA. However, despite being a highly diversified lineage with an estimated 184 extant species, Trichomanes s.l. lack a definitive fossil record, which severely affects the reliability of the molecular dating of this group. Here, we report the first unequivocal fossil record of Trichomanes s.l. as T. angustum comb. nov. on the basis of fertile material with tubular involucres and long exserted receptacles from the mid-Cretaceous Kachin amber, Myanmar. This species was previously tentatively assigned to Hymenophyllites due to a lack of fertile evidence. Inferred to be an epiphytic fern, T. angustum further enriches the species diversity of the epiphytic palaeocommunities in the mid-Cretaceous Kachin amber, which are mainly composed of Porellalean leafy liverworts and Dicranalean and Hypnodendralean mosses. Fossil records indicate that Hymenophyllaceae probably originated in the tropical Pangea at the latest in the Triassic when all continents were coalesced into a single landmass and had already accumulated some notable diversity in low-middle latitude areas of Laurasia by the mid-Cretaceous period.
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