MePHD1.2 affects the synthesis of cyanogenic glycosides by regulating transcription of MeCYP79D2 in cassava

The high content of cyanogenic glycosides (CG) in cassava tubers affects food safety. CG are involved in the plant growth and development and protect cassava leaves from herbivorous predators. However, the regulatory mechanism of CG biosynthesis remains poorly understood. Here, yeast one-hybrid assays were performed using a mixed cDNA library of cassava tubers and leaves as prey and the promoter of MeCYP79D2 as bait. MeCYP79D2, a cytochrome P450 protein, is the rate-limiting enzyme for CG synthesis in cassava. From this information, a candidate regulator of MeCYP79D2 was selected and identified as transcription factor MePHD1.2. MePHD1.2, located in the nucleus and exhibiting an inhibitory transcription activity directly bound to an AT-rich motif in the promoter of MeCYP79D2 . In cassava, the transcriptional activity of MeCYP79D2 was considerably enhanced in mephd1.2 mutant lines leading to increased linamarin and lotaustralin contents. Deletion of MePHD1.2 promoted the production of CGs in cassava and decreased transcription inhibition on MeCYP79D2 , exposing a novel regulatory module governing biosynthesis of CGs.