Clara Sánchez-Rodríguez, KassaDee Ketelaar, Rene Schneider, Jose A. Villalobos, Chris R. Somerville, Staffan Persson, and Ian S. Wallace

Significance

Cellulose is the most abundant biopolymer on Earth and is a critical component for plants to grow and develop. Cellulose is synthesized by large cellulose synthase complexes containing multiple cellulose synthase A (CESA) subunits; however, how cellulose synthesis is regulated remains unclear. In this study, we identify BRASSINOSTEROID INSENSITIVE2 (BIN2) as a protein kinase that directly phosphorylates Arabidopsis CESA1 and further demonstrate that this phosphorylation event negatively regulates CESA activity, and thus cellulose biosynthesis, in Arabidopsis. Therefore, this study provides a clear link between cell wall biosynthesis and hormonal signal transduction pathways that regulate plant growth and development.

Abstract

The deposition of cellulose is a defining aspect of plant growth and development, but regulation of this process is poorly understood. Here, we demonstrate that the protein kinase BRASSINOSTEROID INSENSITIVE2 (BIN2), a key negative regulator of brassinosteroid (BR) signaling, can phosphorylate Arabidopsis cellulose synthase A1 (CESA1), a subunit of the primary cell wall cellulose synthase complex, and thereby negatively regulate cellulose biosynthesis. Accordingly, point mutations of the BIN2-mediated CESA1 phosphorylation site abolished BIN2-dependent regulation of cellulose synthase activity. Hence, we have uncovered a mechanism for how BR signaling can modulate cellulose synthesis in plants.

See: https://www.google.com.vn/?gfe_rd=cr&ei=2WXbWOPgMsOP2ATBmKGIBw

PNAS March 28 2017; vol.114; no.13: 3533–3538

Fig. 1.

Cellulose biosynthesis depends on BR synthesis and signaling. The crystalline cellulose content of 5-d-old dark-grown seedlings was analyzed as described in Materials and Methods. (A) Crystalline cellulose content of wild-type Col-0 (black bars) and det2-1 (white bars) seedlings grown in the presence or absence of 100 nM eBL. (B) Similar analyses were performed for bin2-1 heterozygous (bin2-1^+/−; gray bars) and homozygous (bin2-1^−/−; white bars) mutants in the presence or absence of 5 μM bikinin (BK). Crystalline cellulose contents are reported as a percentage of the crystalline cellulose content of wild-type untreated controls. Error bars for both A and B represent SEM (n = 3 biological replicates per biological replicate, n = 2 technical replicates per biological replicate; ***P < 0.005 by Student’s t test). ns, not significant by Student’s t test.