Regulation of (1,3;1,4)-beta-D-glucan synthesis in developing endosperm of barley lys mutants

The mechanism behind altered content of (1,3:1,4)-beta-D-glucan was investigated in developing endosperm of barley lys3 and lys5 mutants. Both types of mutants are primarily affected in starch biosynthesis, and hence effects on (1,3;1,4)-beta-D-glucan are likely to be pleiotropic. The mutant alleles lys5f and lys5g exerted pronounced effects on the cell wall with increased level of (1,3;1,4)-beta-D-glucan content. The low-starch high-(1,3;1,4)-beta-D-glucan phenotype was most pronounced in lys5f. Among the Cellulose Synthase-Like (CSL) gene members belonging to the families CSLF and CSLH, which all encode (1,3;1,4)-beta-D-glucan synthase proteins, CSLF6 was by far the highest expressed in the wild type, whereas both lys5f and lys5g exhibited a decreased level of CSLF6 transcript. Thus, the lys5 mutants have increased (1,3:1,4)-beta-D-glucan level in spite of lower transcript levels. This suggests the presence of a sensing and signaling system in the cell wall, which in the case of the lys5 mutants caused a decreased transcript level in response to the increased (1,3;1,4)-beta-D-glucan levels. In the lys3a mutant we found a 1000-fold repression of the CSLF6 transcript throughout the whole endosperm development. Thus CSLF6 is under the control of the Lys3 transcriptional regulatory mechanism that operates during barley grain development.