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

The high content of cyanogenic glycosides (CG) in cassava storage tubers seriously affects human food safety. CG play crucial roles in plant growth and development and can protect cassava leaves from being masticated by herbivorous predators. Nevertheless, the regulatory mechanism of CG biosynthesis, which results in a low CG content in storage tubers and high CG content in leaves, remains poorly understood. Here, yeast one-hybrid assay was performed using a mixed cDNA library of cassava storage roots 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, that is, transcription factor MePHD1.2, was selected. MePHD1.2, which is located in the nucleus and exhibits a transcription inhibitory activity, can directly bind to PD2 segment in the promoter of MeCYP79D2, which results in its repressed expression. In cassava, the transcriptional activity of MeCYP79D2 was considerably enhanced in mephd1.2 lines, which caused an increase in the contents of linamarin and lotaustralin. Our findings unveil a novel regulatory module governing CG biosynthesis, wherein mutation of MePHD1.2 attenuates its transcription inhibition on MeCYP79D2 and boosts CGs biosynthesis in cassava.