Combined transcriptome and metabolome analysis reveals that the ZmACS7 gene affects lignin synthesis in maize (Zea mays)

Maize stem lignin content plays a significant role in improving cell wall digestibility and biofuel applications. In this study, we performed transcriptomic and metabolomic analysis using the third internode of the stalk from two inbred lines with contrasting fiber content: the high-fiber inbred line Huangchang b (Hcb) and the low-fiber line Ji63 (Ji63). We performed the analysis using samples from different developmental stages, including the tenth-leaf stage (V10), days at silking (DTS), 10 days after silking (AS10), and 20 days after silking (AS20). We found that the differentially expressed genes (DEGs) are mainly involved in plant hormone signal transduction pathways, especially in the ethylene pathway. Indeed, the expression of ZmACS7 was negatively correlated with stem lignin content. We then investigated the cell wall composition in the ZmACS7 mutant acs7/sdw3 using anatomical, mechanical and biochemical analyses at the three positions: the bottom of the tassel spindle (TBTS), the peduncle stem, and the bottom-third stalk internode. We found that cellulose, hemicellulose, and lignin contents were reduced. This study reveals a key role of the ethylene biosynthetic gene ZmACS7 in stalk fiber accumulation and mechanical strength, and provides a promising target for molecular breeding of lodging-resistant maize varieties.