Mutation of 4-coumarate: coenzyme A ligase 1 gene affects lignin biosynthesis and increases the cell wall digestibility in maize mutants.

BACKGROUND

Maize () mutants associated with impaired lignin biosynthesis are a potential source for the breed of novel germplasms with improved cell wall digestibility. The spontaneous mutants had been identified since 2008. However, the gene responsible for the locus, and the comprehensive effects of mutation on lignin biosynthesis, soluble phenolics accumulation, and cell wall degradation have yet to be elucidated.

RESULTS

The locus was identified to encode a major 4-coumarate: coenzyme A ligase (Zm4CL1) through analyzing MutMap-assisted gene mapping data. Two alleles of isolated from mutants contained two transposons inserted in the first exon and the second intron, respectively, and consequently, the activities of 4CLs in the crude enzyme extracts from midribs were reduced by 51-62% compared with the wild type. Furthermore, five were retrieved from maize genome, and was the most highly expressed one in the lignified tissues. Mutation of mainly impeded the biosynthesis of guaiacyl (G) lignins and increased the level of soluble feruloyl derivatives without impacting maize growth and development. Moreover, both neutral detergent fiber digestibility and saccharification efficiency of cell walls were significantly elevated in the mutant.

CONCLUSIONS

Zm4CL1 was identified as the gene, since two independent alleles of were associated with the same mutant phenotype. Mutation of mainly affected G lignin biosynthesis and soluble feruloyl derivatives accumulation in maize lignified tissues. The reduced recalcitrance of the mutant suggests that is an elite target for cell wall engineering, and genetic manipulation of this gene will facilitate the utilization of crop straw and stover that have to be dealt with for environmental protection.