Rice Brittle culm 6 encodes a dominant-negative form of CesA protein that perturbs cellulose synthesis in secondary cell walls

Abstract

The brittle culm (bc) mutants of Gramineae plants having brittle skeletal structures are valuable materials for studying secondary cell walls. In contrast to other recessive bc mutants, rice Bc6 is a semi-dominant bc mutant with easily breakable plant bodies. In this study, the Bc6 gene was cloned by positional cloning. Bc6 encodes a cellulose synthase catalytic subunit, OsCesA9, and has a missense mutation in its highly conserved region. In culms of the Bc6 mutant, the proportion of cellulose was reduced by 38%, while that of hemicellulose was increased by 34%. Introduction of the semi-dominant Bc6 mutant gene into wild-type rice significantly reduced the percentage of cellulose, causing brittle phenotypes. Transmission electron microscopy analysis revealed that Bc6 mutation reduced the cell wall thickness of sclerenchymal cells in culms. In rice expressing a reporter construct, BC6 promoter activity was detected in the culms, nodes, and flowers, and was localized primarily in xylem tissues. This expression pattern was highly similar to that of BC1, which encodes a COBRA-like protein involved in cellulose synthesis in secondary cell walls in rice. These results indicate that BC6 is a secondary cell wall-specific CesA that plays an important role in proper deposition of cellulose in the secondary cell walls.

Tissue-specific transcriptome analysis within the maturing sugarcane stalk reveals spatial regulation in the expression of cellulose synthase and sucrose transporter gene families

“…Shbk-2 contains the carbohydrate-binding module which has been implicated in modifying cellulose crystallinity in BC1 from rice (Li et al 2003;Liu et al 2013). Coordinate expression of the equivalent CesA subunit and COBRA transcripts in other species has been associated with secondary cell wall synthesis (Ching et al 2006;Kotake et al 2011;Zhang et al 2014), consistent with our finding that these transcripts are expressed in the rind tissue of sugarcane.…”

Characterization and cloning of a brittle culm mutant (bc88) in rice (Oryza sativa L.)

“…msu.edu/), the candidate gene for bc88 encodes a cellulose synthase. Thus, BC88 is related to the cellulose synthesis pathway, consistent with the finding in BC6 [5]. Cellulose is a major component of plant cell wall, which can be grouped into three basic types according to the wall thickness, i.e., parenchyma, collenchyma, and sclerenchma [33].…”

“…More recently, an allelic to BC88, named BC6 has been reported [5]. Although bc88 and bc6 were both obtained by EMS treatment, their wild-type was different, i.e., Wuyunjing 7 variety for the former and IR68 variety for the latter.…”

“…The CesA, first isolated from cotton [4], commonly contains 8 transmembrane domains with a large cytoplasmic region between the 2nd and the 3rd transmembrane domains [5]. So far, 10 CesA genes have been identified in Arabidopsis and 9 in rice and typically classified into 2 groups based on the phylogenetic analysis.…”

Advances in Genetic Manipulation of Lignocellulose to Reduce Biomass Recalcitrance and Enhance Biofuel Production in Bioenergy Crops

“…For cellulose biosynthesis, first CesA compounds gathered into Golgi apparatus and then transmitted to the plasma membrane in three stage: initiation, elongation, and termination [70] In secondary cell walls, the presence of CesA 4 , CesA 7 , and CesA 8 is needed [71], while in PCWs the interaction of CesA 1 , CesA 3 , and CesA 6 (or CesA 1 , CesA 3 , and CesA 6 -releated proteins) is required [68]. In numerous plant species, the CesA families have been distinguished, comprising Arabidopsis [72], rice [73,74], wheat [75], barley [76], maize [77], poplar [78], cotton [79]. Through various genetic approaches numerous specific CesA mutants have been distinguished, which most mutants present reduced cellulose levels and imperfect plant growth ( Table 2).…”