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.
Highlights
Strigolactones (SL) are a group of butanolide-containing molecules originally identified as seed germination stimulants for the parasitic weeds Striga and Orobanche (Cook et al, 1966; Samejima et al, 2016) and later characterized as phytohormones that play diverse important roles in plant growth and development (Al-Babili and Bouwmeester, 2015; Zwanenburg and Blanco-Ania, 2018; Chesterfield et al, 2020)
Same as the other Poaceae family members, sorghum does not encode cytochrome P450s (CYPs) that belong to CYP722C subfamily, but encode four MORE AXILLARY GROWTH1 (MAX1) analogs
To understand the evolutionary relationship of these MAX1 homologs, we conducted a phylogenetic analysis of selected MAX1 analogs from dicotyledons and monocotyledons (Figure 2A; Supplementary Figure 1; Supplementary Table 6)
Summary
Edited by: Sheng-Xiong Huang, Kunming Institute of Botany, Chinese Academy of Sciences (CAS), China. Reviewed by: Jungui Dai, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, China. 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. SbMAX1a (cytochrome P450 711A enzyme in sorghum) synthesized 18-hydroxy-carlactonoic acid (18-hydroxy-CLA) directly from carlactone (CL) through four-step oxidations. 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
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