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 MAX1 analogs and LGS1. Surprisingly, SbMAX1d (accession # XP_002458367) synthesized 18-hydroxy-carlactonoic acid (18-hydroxy-CLA) directly from carlactone (CL) through four-step oxidations, and addition of LGS1 led to the synthesis of both 5-deoxystrigol (5DS) and 4-deoxyorobanchol (4DO). Further biochemical characterization found that LGS1 functions after SbMAX1d by converting 18-hydroxy-CLA to 18-sulphate-CLA to provide an easier leaving group to afford a spontaneous formation of 5DS and 4DO. The unique functions of SbMAX1 and LGS1 imply a previously unknown synthetic route towards strigolactones.

Identification of aPrunusMAX1 Homolog as a Unique Strigol Synthase from Carlactone Bypassing 5-Deoxystrigol

“…1, Os01g0700900) in converting CL to 4DO (17), OsCYP711A3 (Os1400/OsMAX1c in Fig. 1, Os01g0701400) in converting 4DO to OB (17), one of four MAX1 homologs in sorghum SbMAX1a in converting CL to 18-OH-CLA (27,29), and PpMAX1c characterized in this study as a strigol synthase are all unique functions that are only conserved in certain species or genus (Fig. 2A).…”

“…MAX1 homologs are functionally diverse, especially when multiple MAX1 homologs are encoded by one plant species (11, 17, 18, 26, 27). For example, cereal crops generally encode more than one MAX1 homologs (28), with some identified to catalyze the conversion of CL to CLA (a step conserved in all the plants reported so far) (11, 24), some CL to 18-OH-CLA (26, 27, 29), some CL to 4DO (11, 17), and some 4DO to OB (Fig. 1) (11, 17).…”

“…Recent studies indicate the important role of CYP711As in the structural diversity of SLs (17, 18, 27). Although most plants encode only one copy of MAX1 gene with highly conserved function as CLA synthase (11), the presence of multiple copies of MAX1 orthologous genes is not an unusual phenomenon, especially in monocot plants (17, 27, 29), dicotyledonous Leguminosae , and Rosaceae . The activities of OsCYP711A2 (Os900/OsMAX1b in Fig.…”

Ancestral sequence reconstruction of the CYP711 family reveals functional divergence in strigolactone biosynthetic enzymes associated with gene duplication events in monocot grasses

“…It is known that the sulfotransferase LGS1 controls the formation of either orobanchol‐type or strigol‐type SLs (Fig. 1) in Sorghum which can lead to Striga resistance (Gobena et al ., 2017; Wu & Li, 2021; Yoda et al ., 2021). Results from this study suggest that the N71 ancestor can accept 5DS‐like structures as substrates and this opens the possibility of CYP711A forms being involved in further diversification of strigol‐type SLs downstream of 5DS.…”

“…Instead, a sulfotransferase (LGS1) has been shown to catalyze 4DO and 5DS synthesis in sorghum (Fig. 1) (Wu & Li, 2021; Yoda et al ., 2021). Interestingly, within the monocot grasses, gene duplication events of the CYP711A subfamily have delivered multiple subfamily members (as opposed to the one or two CYP711As usually found in other species), including members with A3‐type activities that contribute to orobanchol synthesis (Yoneyama et al ., 2018a).…”