Exploring the molecular mechanism of karrikins and strigolactones

Karrikins force a rethink of strigolactone mode of action

“…27 Instead Scaffidi et al 27 propose that the pyran moiety creates an electronic effect that renders the butenolide susceptible to nucleophilic attack at the carbonyl group. Since a single α/β-hydrolase (KAI2) is active with both KAR and SL in Arabidopsis at least, 18 we propose that the molecular mode of action of both types of molecule involves nucleophilic attack on the common carbonyl group of the butenolide (Fig.…”

“…2 and mechanism 3), followed by hydrolysis of the resulting intermediate. 27 Such a mechanism operating on SL will liberate 5-hydroxy-3-methyl-butenolide and release of the ABC rings (or other leaving group in the case of other active analogs). However, in the case of KAR, the pyran moiety does not function as a leaving group, 27 and therefore it is proposed that the product of hydrolase activity on KAR will spontaneously eliminate water to recreate the original KAR molecule.…”

“…27 Such a mechanism operating on SL will liberate 5-hydroxy-3-methyl-butenolide and release of the ABC rings (or other leaving group in the case of other active analogs). However, in the case of KAR, the pyran moiety does not function as a leaving group, 27 and therefore it is proposed that the product of hydrolase activity on KAR will spontaneously eliminate water to recreate the original KAR molecule. Together with the fact that the D-ring structure alone is not active as a SL, 14,19 we conclude that the process of nucleophilic attack on the butenolide of SL and KAR is essential for activity, rather than the products of the reaction.…”

Molecular mechanism of strigolactone perception by DWARF14

“…The d3/max2/rms4 mutants are also SL insensitive 1,2 . D3/ MAX2/RMS4 genes encode members of the F-box-family protein [17][18][19][20] that participate in an Skp-cullin-F box (SCF) complex 18 and have diverse roles in the plant lifecycle 14,[21][22][23][24][25][26][27][28][29][30] . Recently, it has been reported that petunia DAD2, an orthologue of rice DWARF14 (D14) protein, can hydrolyse the enol ether linkage of GR24 and interacts with PhMAX2A, a petunia orthologue of Arabidopsis MAX2 protein, indicating that the formation of the DAD2-PhMAX2A complex initiates an SCF-mediated signal transduction pathway 31 .…”

From little things big things grow: karrikins and new directions in plant development

“…Thermal destabilisation of KAI2 can, however, come about through addition of the non-natural enantiomer GR24 ent-5DS , which is also a hydrolytic substrate for KAI2, suggesting that mechanistically KAI2 and D14 work in a similar fashion as enzyme-receptors. At this time there is no direct evidence that karrikins are hydrolysed by KAI2, perhaps because karrikins are not expected to be destroyed by nucleophillic attack upon the butenolide ring (Scaffidi et al 2012;Waters et al 2012b). Thus some data do not fully support a simple interpretation that KAI2 binds and hydrolyses KAR 1 directly, with the same outcomes as when D14 binds strigolactones.…”