A Unique Sulfotransferase-Involving Strigolactone Biosynthetic Route in Sorghum

Abstract

LOW GERMINATION STIMULANT 1 (LGS1) plays an important role in strigolactones (SLs) biosynthesis and Striga resistance in sorghum, but the catalytic function remains unclear. Using the recently developed SL-producing microbial consortia, we examined the activities of sorghum MORE AXILLARY GROWTH1 (MAX1) analogs and LGS1. Surprisingly, SbMAX1a (cytochrome P450 711A enzyme in sorghum) synthesized 18-hydroxy-carlactonoic acid (18-hydroxy-CLA) directly from carlactone (CL) through four-step oxidations. The further oxidated product orobanchol (OB) was also detected in the microbial consortium. Further addition of LGS1 led to the synthesis of both 5-deoxystrigol (5DS) and 4-deoxyorobanchol (4DO). Further biochemical characterization found that LGS1 functions after SbMAX1a by converting 18-hydroxy-CLA to 5DS and 4DO possibly through a sulfonation-mediated pathway. The unique functions of SbMAX1 and LGS1 imply a previously unknown synthetic route toward SLs.

Nutritional and tissue-specific regulation of cytochrome P450 CYP711AMAX1homologues and strigolactone biosynthesis in wheat

“…However, five MAX1 homologues have been identified in the rice genome ( Zhang et al , 2014 ), while more recent studies showed that the presence of multiple MAX1 genes is a common characteristic in grasses. More specifically, maize has three MAX1 genes ( Yoneyama et al , 2018 ), sorghum has four ( Wu and Li, 2021 ), and B. distachyon has five ( Changenet et al , 2021 ). According to some studies, MAX1s from grasses fall into four different clades ( Marzec et al , 2020 ; Wu and Li, 2021 ), whereas Vinde et al (2022) only accounted for the presence of three separate groups.…”

“…More specifically, maize has three MAX1 genes ( Yoneyama et al , 2018 ), sorghum has four ( Wu and Li, 2021 ), and B. distachyon has five ( Changenet et al , 2021 ). According to some studies, MAX1s from grasses fall into four different clades ( Marzec et al , 2020 ; Wu and Li, 2021 ), whereas Vinde et al (2022) only accounted for the presence of three separate groups. The multiple MAX1 homologues have been suggested to catalyse different steps in the conversion of CL to bioactive SL molecules.…”

“…Studies in those species have shown that different CYP711A/MAX1 proteins catalyse different steps downstream of CL and might be responsible for the large structural diversity of bioactive SLs found in plants ( Fig. 1B ) ( Yoneyama et al , 2018 ; Wu and Li, 2021 ). In rice, CLA is an intermediate for the conversion of CL to 4-deoxyorobanchol (4DO) by Os900 (CYP711A2), while Os1400 (CYP711A3) converts 4DO to orobanchol ( Zhang et al , 2014 ; Yoneyama et al , 2018 ).…”

“…More specifically, SbMAX1a was found to convert CL to 18-hydroxy-CLA. The latter is used as a substrate by a sulfotransferase encoded by LOW GERMINATION STIMULANT 1 , which is probably involved in the biosynthesis of 5-deoxystrigol (5DS) and 4DO ( Wu and Li, 2021 ). Recent studies have provided insights into the phylogeny of MAX1 genes in monocotyledons, but most of the studies either did not include wheat sequences or did not include all MAX1 genes present in the wheat genome ( Yoneyama et al , 2018 ; Marzec et al , 2020 ; Wu and Li, 2021 ; Vinde et al , 2022 ).…”

Strigolactones as a hormonal hub for the acclimation and priming to environmental stress in plants

“…Beyond arabidopsis, the pathway downstream of carlactone to generate different structures of canonical strigolactones may entail, for example, several paralogues of the CYP711A MAX1 cooperating sequentially, as in rice (Yoneyama et al, 2018 ; Y. Zhang et al, 2014 ). It may also recruit, downstream of MAX1 orthologues, other CYP450 enzymes such as CYP722C isoforms in cotton ( Gossypium arboretum ), tomato ( Solanum lycopersicum ) and cowpea ( Vigna unguiculata ) (Wakabayashi et al, 2019 , 2020 ), or the CYP728B35 LOW GERMINATION STIMULANT1 (LGS1) in sorghum ( Sorghum bicolour ) (Gobena et al, 2017 ; Wu & Li, 2021 ). The CYP712G1 enzyme of tomato was very recently shown to oxidize orobanchol to didehydro‐orobanchol isomers, one of which can be further converted to solanacol (Y. Wang, Durairaj, et al, 2022 ).…”