Silencing of ShMYB58/63 and ShMYB85 in Saccharum spp. Alters Lignin Deposition and Can Improve Biomass Saccharification

Abstract

A primary focus in reducing biomass recalcitrance in plants to produce second-generation bioethanol (E2G) has been the genetic manipulation of transcription factors (TFs) that regulate lignin content and composition. Little is known about lignin regulation in monocots, particularly in sugarcane, which is a promising feedstock for E2G production. We conducted a Bayesian network analysis that identified sugarcane orthologs ShMYB85 and ShMYB58/63 as potential activators of lignin biosynthesis in sugarcane. Then, we generated silenced transgenic lines for these TFs in the Saccharum spp. hybrid cultivar SP80-3280 to investigate their roles in lignin biosynthesis (the two Saccharum species, S. officinarum and S. spontaneum, were used only as the dataset for the network and expression analyses). Characterization of the transgenic lines revealed significant alterations in lignin content and composition. Notably, saccharification efficiency was enhanced in the shmyb85 transgenic lines, suggesting that shmyb85 may act as a broader activator than shmyb58/63. Our findings highlight the opportunities and challenges associated with redesigning the sugarcane cell wall through the genetic manipulation of myb TFs, ultimately aiming to enhance E2G production.