A which is an intermediated compound in the SL

lower concentration of Strigolactones in the plants treated with inhibitors of
carotenoid biosynthesis and total nonappearance of strigolactones in carotenoid insufficient mutants put forward for thought that
strigolactones were inferred from carotenoids.

A wide
collection of shoot branching mutants that were deficient in strigolactones biosynthesis
or signalling helped to understand and define the assembly of strigolactones
biosynthesis and signalling pathways and lead to a proposed strigolactones biosynthesis
pathway. These branching mutants are Arabidopsis thaliana known as more axillary growth
(max) mutants, Oryza sativa dwarf
(d) or high-tillering dwarf or (htd) mutants, Pisum sativum ramosus (rms) mutants and Petunia hybrida decreased apical dominance (dad) mutants.

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The advanced
discovery of regulation of shoot branching and tillering by strigolactones
exhibited that the two carotenoid cleavage dioxygenases
(CCDs), CCD7 and CCD8,
encoded by MAX3/RMS5/D17(HTD1)/DAD3 and MAX4/RMS1/D10/DAD1 respectively. Theses CCDs catalyses
the oxidative cleavage of carotenoid double bonds to release carbonyl products
called apocarotenoids.


The excusive
substrate for strigolactones biosynthesis is trans-?-carotene. The plants a stereo-selective enzyme lycopene- ?-cyclase, catalyse the conversion of ?-carotene forms to all-trans-configured ?-carotene. These trans-configured – ?-carotene are converted into 9-cis-?-carotene
(C-40) by the activity of
?-carotene isomerase, encoded by D27 in Arabidopsis. The later acts as substrate for CCD7 which cleaves cis-configured carotenoids into 9-cis-?-apo-10′-carotenal (C-27) and ?-ionone (C-13) (Schwartz et al., 2004; Alder et al., 2012; Waters et al., 2012a). CCD8 then acts on the 9-cis-?-apo-10′-carotenal product of enzymatic cleavage to form a strigolactone-like
compound named Carlactone (CL), which is an intermediated compound in the SL
pathway containing only A and D rings with enol ether bridge (Alder et al., 2012). Cytochrome P450 of the
CYP711A1clade encoded by MAX1 in Arabidopsis is responsible for the conversion
of Carlactone into functional SLs such as 5-deoxystrigol (Stirnberg et al., 2002; Booker et al., 2004; Alder et al., 2012). The
rearrangements and modifications (hydroxylation, oxidation) caused by MAX1,
converts Carlactone to carlactonic acid (CLA) then further transformed to
methyl carlactonoate (MeCLA) by an unknown enzyme (Abe et al., 2014). In rice,
one MAX1 paralogue converts carlactone into ent-20-epi-5-deoxystrigol, the
presumed precursor of rice SL.


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