Identification and characterization of sorgomol synthase in sorghum strigolactone biosynthesis

Abstract

Strigolactones (SLs), first identified as germination stimulants for root parasitic weeds, act as endogenous phytohormones regulating shoot branching and as root-derived signal molecules mediating symbiotic communications in the rhizosphere. Canonical SLs typically have an ABCD ring system and can be classified into orobanchol- and strigol-type based on the C-ring stereochemistry. Their simplest structures are 4-deoxyorobanchol (4DO) and 5-deoxystrigol (5DS), respectively. Diverse canonical SLs are chemically modified with one or more hydroxy or acetoxy groups introduced into the A- and/or B-ring of these simplest structures, but the biochemical mechanisms behind this structural diversity remain largely unexplored. Sorgomol in sorghum (Sorghum bicolor [L.] Moench) is a strigol-type SL with a hydroxy group at C-9 of 5DS. In this study, we characterized sorgomol synthase. Microsomal fractions prepared from a high-sorgomol-producing cultivar of sorghum, Sudax, were shown to convert 5DS to sorgomol. A comparative transcriptome analysis identified SbCYP728B subfamily as candidate genes encoding sorgomol synthase. Recombinant SbCYP728B35 catalyzed the conversion of 5DS to sorgomol in vitro. Substrate specificity revealed that the C-8bS configuration in the C-ring of 5DS stereoisomers was essential for this reaction. The overexpression of SbCYP728B35 in Lotus japonicus hairy roots, which produce 5DS as an endogenous SL, also resulted in the conversion of 5DS to sorgomol. Furthermore, SbCYP728B35 expression was not detected in nonsorgomol-producing cultivar, Abu70, suggesting that this gene is responsible for sorgomol production in sorghum. Identification of the mechanism modifying parental 5DS of strigol-type SLs provides insights on how plants biosynthesize diverse SLs.

A Unique Sulfotransferase-Involving Strigolactone Biosynthetic Route in Sorghum

“…There is likely other enzyme(s) involved downstream of or simultaneous with LGS1 to guarantee the conversion of 18-sulfate-CLA to 5DS exclusively instead of a 4DO/5DS mixture in sorghum. We, thus, examined the function of SbMAX1b-1d, SbCYP722B, SbCYP728B35, SbCYP728B1, and ZmCYP728B35 in the 4DO/5DS/18-hydroxy-CLA-producing consortium ECL/YSL8a (resulting ECL/YSL9-10, Supplementary Table 3 ; Wakabayashi et al, 2021 ). However, we were unable to see any changes to the ratio between 5DS and 4DO ( Supplementary Figure 9 ).…”

A unique sulfotransferase-involving strigolactone biosynthetic route in Sorghum

“…There is likely other enzyme(s) involved downstream of or simultaneous with LGS1 to guarantee the conversion of 18-sulphate-CLA to 5DS exclusively instead of a 4DO/5DS mixture. We thus examined the function of SbMAX1a, 1b, 1c, SbCYP722B, SbCYP728B35, SbCYP728B1, and ZmCYP728B35 in the 4DO/5DS/18-hydroxy-CLA-producing consortium ECL/YSL8a (resulting ECL/YSL9-10 , Table S2) 25 . Unfortunately, we were unable to see any changes to the ratio between 5DS and 4DO (Figure S9).…”

Establishment of strigolactone-producing bacterium-yeast consortium

“…For example, Striga -susceptible maize cultivar only produces 5DS, while mainly sorgomol is detected in the resistant cultivar ( 60 ); Sorghum produces both 5DS and sorgomol and can convert 5DS to sorgomol ( 26 ). Recently, CYP728B35 encoded by Sorghum has been suggested to be the sorgomol synthase catalyzing the hydroxylation of 5DS to afford the synthesis of sorgomol ( 61 ). In addition to Sorghum, strigol-producing cotton converts 5DS to strigol and strigyl acetate ( 26 ).…”