Expression of sugarcane COBRA-Like genes, ScBC1 and ScBC1L2, increases plant biomass

Cellulose is a major determinant of plant biomass yield and quality, with significant industrial relevance. COBRA proteins are established regulators of cellulose deposition and cell wall organization; however, their roles in sugarcane (Saccharum spp.) growth and development remain uncharacterized. A genome-wide analysis identified 50 sugarcane COBRA genes grouped into 11 unigenes, with ScBC1 (Brittle Culm 1) and ScBC1L2 (Brittle Culm Like 2) highly expressed in stems. Phylogenetic analysis placed ScBC1 with secondary cell wall-associated genes, including maize ZmBK2, while ScBC1L2 clustered with primary cell wall-related genes. Transient expression of ScBC1 and ScBC1L2 in Nicotiana benthamiana increased leaf biomass and epidermal cell size, with ScBC1 having the strongest effect. Virus-induced gene silencing of ZmBK2 in maize reduced biomass, cellulose content, and cell area, and altered the expression of Cellulose Synthase (CesA) genes. Genes related to cell wall remodeling, including Expansin, β-Galactosidase, and Polygalacturonase, were differentially expressed in ZmBK2-silenced leaves, suggesting compensatory responses. These findings indicate a conserved role of the ScBC1–ZmBK2 subclade in cellulose deposition and cell expansion, identifying ScBC1 as a promising target for improving sugarcane biomass.