Browsing by Author "Ashton, Neil W."

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    An Analysis of Auxin Distribution and Activity during Photomorphogenesis and Skotomorphogenesis in the moss, Physcomitrella patens
    (Faculty of Graduate Studies and Research, University of Regina, 2015-07) Robinson, Shawn Riley; Ashton, Neil W.; Weger, Harold; Dahms, Tanya
    Plant development varies depending on whether it occurs in the light (photomorphogenesis) or in the dark (skotomorphogenesis). This phenomenon has been studied in depth in flowering plants such as Arabidopsis thaliana but remains largely unexplored in more ancient plant groups such as the bryophytes, which include the model moss, Physcomitrella patens, despite decades-old awareness of the markedly different gametophytic morphologies that result from photomorphogenesis and skotomorphogenesis in this moss. Research undertaken with Arabidopsis has elucidated in detail roles for various phytohormones, including auxin, in regulating the reversible developmental interconversion of photomorphogenesis and skotomorphogenesis. By contrast, although auxin has previously been shown to be active at many stages of Physcomitrella development, its specific involvement in photomorphogenesis and skotomorphogenesis and their interconversion, especially in relation to gametophore development, is unknown. Through the use of transgenic auxin-responsive GUS reporter strains in conjunction with auxin signalling and polar transport inhibitors it was shown that auxin is critically important for the development of gametophore stems and leaves in Physcomitrella during photomorphogenesis but it has a diminished role in leaf development and is not required for stem elongation during skotomorphogenesis. However, auxin is required for the gametophore bud to leafy gametophore transition in a dark-dependent manner and for protonemal development both in the dark and in the light. The roles of auxin in development of the moss gametophore are very similar to those in hypocotyl elongation in Arabidopsis, implying that they are ancient and have been highly conserved during land plant evolution.
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    The polyketide pathway in sporopollenin biosynthesis is specific to land plants (Embryophyta)
    (BioRxiv, 2024-10-19) Sraan, Damanpreet K.; Ashton, Neil W.; Suh, Dae-Yeon
    Background and Aims: Sporopollenin (SP) is a complex biopolymer in the outer wall of spores and pollen and provides protection from environmental stresses. Its extraordinary chemical resistance, especially to acetolysis, was widely used to identify SP in biological specimens. This broad definition of SP led to claims for its widespread occurrence among diverse embryophyte and non-embryophyte taxa. We previously proposed a biochemical definition that can be used to distinguish genuine SP from other chemically resistant cell wall materials. The definition was centred on ASCL (Anther-Specific Chalcone synthase-Like), an embryophyte-specific enzyme of the polyketide pathway that provides precursors for SP biosynthesis. Herein, we examine the evolution and distribution of all five enzymes (CYP703A, CYP704B, ACOS, ASCL and TKPR) of the polyketide pathway and propose a new, more comprehensive definition of SP. Methods: We performed BLASTp searches, phylogenetic tree construction, protein modeling and sequence analysis to determine the presence or absence of ACOS and TKPR in embryophytes and streptophytic algae. Key Results: We found evidence that all five enzymes of the polyketide pathway evolved from ancestral enzymes of primary metabolism and ACOS, ASCL and TKPR were co-selected during evolution. The dosage of all five genes has been subjected to strict evolutionary control and, in some taxa, synteny has provided a selective advantage. All five enzymes are present in embryophytes but absent in green algae, indicating that the polyketide pathway and therefore SP is embryophyte-specific. Conclusions: The addition of the polyketide pathway in the definition of genuine SP will allow separation of SP from algaenans and other chemically resistant ‘SP-like’ algal spore wall substances. This study further signifies SP as an evolutionary innovation unique to the embryophyte lineage and encourages research on possible evolutionary relationship between algal spore wall ‘SP-like materials’ and embryophyte SP. Competing Interest Statement The authors have declared no competing interest.