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Publication - Dr Jill Harrison

    A KNOX-cytokinin regulatory module predates the origin of indeterminate vascular plants

    Citation

    Coudert, Y, Novak, O & Harrison, CJ, 2019, ‘A KNOX-cytokinin regulatory module predates the origin of indeterminate vascular plants’. Current Biology, vol 29., pp. 2743 - 2750

    Abstract

    The diverse forms of today’s dominant vascular plant flora are generated by the sustained proliferative activity of sporophyte meristems at plants’ shoot and root tips, a trait known as indeterminacy [1]. Bryophyte sister lineages to the vascular plants lack such indeterminate meristems and have an overall sporophyte form comprising a single small axis which ceases growth in the formation of a reproductive sporangium [1]. Genetic mechanisms regulating indeterminacy are well characterised in flowering plants, involving a feedback loop between Class I KNOX genes and cytokinin [2, 3], and Class I KNOX expression is a conserved feature of vascular plant meristems [4]. The transition from determinate growth to indeterminacy during evolution was a pre-requisite to vascular plant diversification, but mechanisms enabling the innovation of indeterminacy are unknown [5]. Here we show that Class I KNOX gene activity is necessary and sufficient for axis extension from an intercalary region of determinate moss shoots. As in Arabidopsis, Class I KNOX activity promotes cytokinin biosynthesis by an ISOPENTENYL TRANSFERASE gene, PpIPT3. PpIPT3 promotes axis extension, and PpIPT3 and exogenously applied cytokinin can partially compensate for loss of Class I KNOX function. By outgroup comparison, the results suggest that a pre-existing KNOX-cytokinin regulatory module was recruited into vascular plant shoot meristems during evolution to promote indeterminacy, thereby enabling the radiation of vascular plant shoot forms.

    Full details in the University publications repository