Cytokinin <i>N</i>-glucosides: Occurrence, Metabolism and Biological Activities in Plants

oleh: Eva Pokorná, Tomáš Hluska, Petr Galuszka, H. Tucker Hallmark, Petre I. Dobrev, Lenka Záveská Drábková, Tomáš Filipi, Katarína Holubová, Ondřej Plíhal, Aaron M. Rashotte, Roberta Filepová, Jiří Malbeck, Ondřej Novák, Lukáš Spíchal, Břetislav Brzobohatý, Pavel Mazura, Lenka Zahajská, Václav Motyka

Format: Article
Diterbitkan: MDPI AG 2020-12-01

Deskripsi

Cytokinins (CKs) are a class of phytohormones affecting many aspects of plant growth and development. In the complex process of CK homeostasis in plants, <i>N</i>-glucosylation represents one of the essential metabolic pathways. Its products, CK <i>N</i>7- and <i>N</i>9-glucosides, have been largely overlooked in the past as irreversible and inactive CK products lacking any relevant physiological impact. In this work, we report a widespread distribution of CK <i>N</i>-glucosides across the plant kingdom proceeding from evolutionary older to younger plants with different proportions between <i>N</i>7- and <i>N</i>9-glucosides in the total CK pool. We show dramatic changes in their profiles as well as in expression levels of the <i>UGT76C1</i> and <i>UGT76C2</i> genes during <i>Arabidopsis</i> ontogenesis. We also demonstrate specific physiological effects of CK <i>N</i>-glucosides in CK bioassays including their antisenescent activities, inhibitory effects on root development, and activation of the CK signaling pathway visualized by the CK-responsive YFP reporter line, <i>TCSv2::3XVENUS</i>. Last but not least, we present the considerable impact of CK <i>N</i>7- and <i>N</i>9-glucosides on the expression of CK-related genes in maize and their stimulatory effects on CK oxidase/dehydrogenase activity in oats. Our findings revise the apparent irreversibility and inactivity of CK <i>N</i>7- and <i>N</i>9-glucosides and indicate their involvement in CK evolution while suggesting their unique function(s) in plants.