Working model for the interaction between the Yang cycle and NA biosynthesis. In WT, to sustain a high flow of NA synthesis the byproduct MTA is hydrolyzed by MTN and recycled in the Yang cycle. However, in the mic1, mutation of ZmMTN1 impaired MTA salvage; thereby the accumulated MTA represses NAS activity. Insufficient NA supply led to Fe deficiency and interveinal chlorosis. Fe deficiency induced the expression of enzymes associated with DMA synthesis but accelerated NA consumption. Enzymes are indicated in blue color, while compounds are represented in black letters. The black arrows/lines indicate pathways reported previously, while red lines/arrows indicate regulations identified in the mic1 mutant in this study.