Strigolactone Regulates Leaf Senescence in Concert with Ethylene in Arabidopsis

Abstract

Leaf senescence is not a passive degenerative process; it represents a process of nutrient relocation, in which materials are salvaged for growth at a later stage or to produce the next generation. Leaf senescence is regulated by various factors, such as darkness, stress, aging, and phytohormones. Strigolactone is a recently identified phytohormone, and it has multiple functions in plant development, including repression of branching. Although strigolactone is implicated in the regulation of leaf senescence, little is known about its molecular mechanism of action. In this study, strigolactone biosynthesis mutant strains of Arabidopsis (Arabidopsis thaliana) showed a delayed senescence phenotype during dark incubation. The strigolactone biosynthesis genes MORE AXIALLY GROWTH3 (MAX3) and MAX4 were drastically induced during dark incubation and treatment with the senescence-promoting phytohormone ethylene, suggesting that strigolactone is synthesized in the leaf during leaf senescence. This hypothesis was confirmed by a grafting experiment using max4 as the stock and Columbia-0 as the scion, in which the leaves from the Columbia-0 scion senesced earlier than max4 stock leaves. Dark incubation induced the synthesis of ethylene independent of strigolactone. Strigolactone biosynthesis mutants showed a delayed senescence phenotype during ethylene treatment in the light. Furthermore, leaf senescence was strongly accelerated by the application of strigolactone in the presence of ethylene and not by strigolactone alone. These observations suggest that strigolactone promotes leaf senescence by enhancing the action of ethylene. Thus, dark-induced senescence is regulated by a two-step mechanism: induction of ethylene synthesis and consequent induction of strigolactone synthesis in the leaf.

Influence of Strigolactone (GR24) as a Seed Treatment on Growth, Gas Exchange and Chlorophyll Fluorescence of Wheat under Saline Conditions

“…Strigolactones are produced in two forms (as endogenous hormones and root secretions). Strigolactones are involved in various roles like promoting symbiotic interactions (arbuscular mycorrhizal fungi) (Evangelisti et al, 2014); enhancing cell elongation within the root but inhibiting root hairs and asymmetric root growth ; affecting developmental processes (Yoneyama et al, 2013), involving in light harvesting mechanism (Mayzlish-Gati et al, 2010) and leaf senescence (Woo et al, 2001); performing cross-talk with other major hormones like auxin, ABA and ethylene ; controlling leaf shape, lamina joint inclination and tiller angle (Sang, 2014); delaying leaf senescence and reducing secondary growth and controlling PCD (Programmed cell death), photomorphogenesis and modulating biotic/abiotic stress responses (Xiong et al, 2014;Ha et al, 2014;Ueda and Kusaba, 2015). Strigolactones are widely distributed and GR24 is its synthetic analogue (Gomez-Roldan et al, 2008;Tsuchiya and McCourt, 2009).…”

Structural diversity of strigolactones and their distribution in the plant kingdom

“…In 2008, SLs or their further metabolites were shown to be a novel class of plant hormone inhibiting shoot branching. 10,11) These findings attracted researchers to study the biological functions of SLs and they have been shown to be involved in the regulation of growth of lateral roots and root hairs, 12,13) secondary growth, 14) photomorophogenesis 15) and leaf senescence, 16,17) and to promote root colonization by root nodule bacteria. [18][19][20][21] Approximately 25 natural SLs have been characterized from root exudates of various plant species.…”

Strigolactone biosynthesis and signaling in plant development

“…Pea, Arabidopsis, rice and petunia mutants with defects in SL biosynthesis or SL responses were first identified based on their increased shoot branching phenotypes and their dwarfism (Beveridge et al, 1996;Ishikawa et al, 2005;Napoli, 1996;Stirnberg et al, 2002). Less obvious phenotypes, such as reduced secondary growth, delay in leaf senescence or modified root architecture, were later identified (Brewer et al, 2013;Ueda and Kusaba, 2015;Yamada et al, 2014). SLs can also modulate tolerance to abiotic stresses (drought) (Ha et al, 2014).…”