Seed hemicelluloses tailor mucilage properties and salt tolerance.

Bo Yang,Florian Hofmann,Cătălin Voiniciuc,Björn Usadel

doi:10.1111/nph.17056

Abstract

While Arabidopsis seed coat epidermal cells have become an excellent genetic system to study the biosynthesis and structural roles of various cell wall polymers, the physiological function of the secreted mucilaginous polysaccharides remains ambiguous. Seed mucilage is shaped by two distinct classes of highly substituted hemicelluloses along with cellulose and structural proteins, but their interplay has not been explored. We deciphered the functions of four distinct classes of cell wall polymers by generating a series of double mutants with defects in heteromannan, xylan, cellulose, or the arabinogalactan protein SALT-OVERLY SENSITIVE 5 (SOS5), and evaluating their impact on mucilage architecture and seed germination during salt stress. We discovered that muci10 seeds, lacking heteromannan branches, had elevated tolerance to salt stress, while heteromannan elongation mutants exhibited reduced germination in calcium chloride (CaCl2 ). By contrast, xylan made by MUCILAGE-RELATED21 (MUCI21) was found to be required for the adherence of mucilage pectin to microfibrils made by CELLULOSE SYNTHASE5 (CESA5) as well as to a SOS5-mediated network. Our results indicate that the substitution of xylan and glucomannan in seeds can fine-tune mucilage adherence and salt tolerance, respectively. The study of germinating seeds can thus provide insights into the synthesis, modification and function of complex glycans.

Highlights

Our results indicate that the substitution of xylan and glucomannan in seeds can fine-tune mucilage adherence and salt tolerance, respectively
Cellulose microfibrils are deposited around plant cells and enmeshed in a complex matrix of hemicelluloses, pectin, and, to a lesser extent, structural proteins
Arabidopsis thaliana has nine CELLULOSE SYNTHASE-LIKE A (CSLA) genes that are at least putatively involved in the synthesis of heteromannan (HM), a class of hemicellulose mainly built of β-1,4-linked mannosyl units

Summary

While Arabidopsis seed coat epidermal cells have become an excellent genetic system to study the biosynthesis and structural roles of various cell wall polymers, the physiological function of the secreted mucilaginous polysaccharides remains ambiguous. Seed mucilage is shaped by two distinct classes of highly substituted hemicelluloses along with cellulose and structural proteins, but their interplay has not been explored. We deciphered the functions of four distinct classes of cell wall polymers by generating a series of double mutants with defects in heteromannan, xylan, cellulose, or the arabinogalactan protein SALT-OVERLY SENSITIVE 5 (SOS5), and evaluating their impact on mucilage architecture and on seed germination during salt stress. We discovered that muci[10] seeds, lacking heteromannan branches, had elevated tolerance to salt stress, while heteromannan elongation mutants exhibited reduced germination in. Our results indicate that the substitution of xylan and glucomannan in seeds can fine-tune mucilage adherence and salt tolerance, respectively. The study of germinating seeds can provide insights into the synthesis, modification and function of complex glycans

Introduction

Materials and Methods

Figures and statistical analysis

Results and Discussion