Carlactone-type strigolactones and their synthetic analogues as inducers of hyphal branching in arbuscular mycorrhizal fungi.
Hyphal branching in the vicinity of host roots is a host recognition response of arbuscular mycorrhizal fungi. This morphological event is elicited by strigolactones. Strigolactones are carotenoid-derived terpenoids that are synthesized from carlactone and its oxidized derivatives. To test the possibility that carlactone and its oxidized derivatives might act as host-derived precolonization signals in arbuscular mycorrhizal symbiosis, carlactone, carlactonoic acid, and methyl carlactonoate as well as monohydroxycarlactones, 4-, 18-, and 19-hydroxycarlactones, were synthesized chemically and evaluated for hyphal branching-inducing activity in germinating spores of the arbuscular mycorrhizal fungus Gigaspora margarita. Hyphal branching activity was found to correlate with the degree of oxidation at C-19 methyl. Carlactone was only weakly active (100 ng/disc), whereas carlactonoic acid showed comparable activity to the natural canonical strigolactones such as strigol and sorgomol (100 pg/disc). Hydroxylation at either C-4 or C-18 did not significantly affect the activity. A series of carlactone analogues, named AD ester and AA'D diester, was synthesized by reacting formyl Meldrum's acid with benzyl, cyclohexylmethyl, and cyclogeranyl alcohols (the A-ring part), followed by coupling of the potassium enolates of the resulting formylacetic esters with the D-ring butenolide. AD ester analogues exhibited moderate activity (1 ng-100 pg/disc), while AA'D diester analogues having cyclohexylmethyl and cyclogeranyl groups were highly active on the AM fungus (10 pg/disc). These results indicate that the oxidation of methyl to carboxyl at C-19 in carlactone is a prerequisite but BC-ring formation is not essential to show hyphal branching activity comparable to that of canonical strigolactones.
Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan. Electronic address: sv201042@edu.osakafu-u.ac.jp.
Narumi
N
Mori
Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan. Electronic address: mt201042@edu.osakafu-u.ac.jp.
Kenta
K
Nishiuma
Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan. Electronic address: ss201019@edu.osakafu-u.ac.jp.
Takuya
T
Sugiyama
Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan. Electronic address: hayashi@biochem.osakafu-u.ac.jp.
Hideo
H
Hayashi
Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan. Electronic address: akiyama@biochem.osakafu-u.ac.jp.
Kohki
K
Akiyama
D005658:Fungi / Q000737:chemistry*; D055137:Glomeromycota / Q000737:chemistry; D025301:Hyphae / Q000187:drug effects; D007783:Lactones / Q000737:chemistry / Q000494:pharmacology*; D015394:Molecular Structure; D038821:Mycorrhizae / Q000502:physiology*; D010084:Oxidation-Reduction; D018517:Plant Roots / Q000382:microbiology; D013329:Structure-Activity Relationship; D013559:Symbiosis / Q000502:physiology
D007783:Lactones; C571055:carlactone; C483518:strigol
Arbuscular mycorrhizal symbiosis; Carlactone; Carlactonoic acid; Gigaspora margarita; Glomeromycota; Hyphal branching; Strigolactone; Synthetic analogue