FIDDLEHEAD, a gene required to suppress epidermal cell interactions in Arabidopsis, encodes a putative lipid biosynthetic enzyme

Functional characterization of beta-ketoacyl-CoA synthase genes from Brassica napus L

Seed-specifically expressed beta-ketoacyl-CoA synthase genes of Brassica napus (Bn-FAE1.1 genes) were cloned from two cultivars, namely Askari, a high-erucic-acid type, and Drakkar, a low-erucic-acid type. The genes from the two cultivars were found to be nearly identical. They encode proteins of 507 amino acids, the sequences of which differ only at position 282. The Bn-FAE1.1 gene of Askari, unlike that of Drakkar, was functionally expressed in yeast cells suggesting that the single amino acid exchange effects the low erucic acid phenotype at the E1 gene locus. In yeast cells the beta-ketoacyl-CoA synthase of Askari elongated not only oleoyl but also palmitoleoyl groups as well as saturated acyl groups in such a way that monounsaturated acyl groups of 22 carbons and saturated ones of 26 carbons were formed as main products. A reporter gene fused to the promoter region of the Bn-FAE1.1 gene from Askari showed seed-specific expression in transgenic rapeseed plants. Over-expression of the coding region of the Askari gene in developing seeds of transgenic Drakkar plants resulted in a significant increase in the levels of eicosenoic acid and erucic acid esterified in the seed oil. On the other hand, in transgenic high-erucic-acid rapeseed plants the increase in erucic acid level was at most 60% although the chimeric Bn-FAE1.1 gene was co-expressed with an erucoyl-CoA-specific lysophosphatidate acyltransferase gene enabling trierucoyl glycerol to accumulate in the seed oil.

The maize CR4 receptor-like kinase mediates a growth factor-like differentiation response

The maize crinkly4 (cr4) gene encodes a predicted receptor kinase that is required for the normal differentiation of leaf epidermis (Becraft et al., 1996). Here we confirm that the presumptive cytoplasmic domain is capable of autophosphorylation on serine and threonine residues. The cr4 transcript is most abundant in young developing tissues of the shoot but was not detected in the root. Phenotypic analysis of strong mutant alleles indicates that cr4 functions throughout shoot development to control the differentiation of internal as well as epidermal tissues. However, epidermal cells appear most sensitive to perturbations in CR4 signaling because epidermal defects are more pronounced than internal cell defects. Epidermal cells show irregularities in shape, cell wall thickness and structure, cuticle formation, and vesicle trafficking. Some plants show tumor-like proliferations of cells on the leaves. Thus CR4 regulates an array of developmental responses including cell proliferation, fate, pattern, and differentiation suggesting a function analogous to growth factor responses in animals.

Transgenic Arabidopsis plants expressing a fungal cutinase show alterations in the structure and properties of the cuticle and postgenital organ fusions

A major structural component of the cuticle of plants is cutin. Analysis of the function of cutin in vivo has been limited because no mutants with specific defects in cutin have been characterized. Therefore, transgenic Arabidopsis plants were generated that express and secrete a cutinase from Fusarium solani f sp pisi. Arabidopsis plants expressing the cutinase in the extracellular space showed an altered ultrastructure of the cuticle and an enhanced permeability of the cuticle to solutes. In addition, pollen could germinate on fully differentiated leaves of cutinase-expressing plants but not on control leaves. These differences coincided with strong postgenital organ fusions. The junctions of the fusions contained pectic polysaccharides. As fused organs grew apart from each other, organ deformations and protrusions of epidermal cells developed at positions with high mechanical stress. These results demonstrate that an intact cutin layer not only is important for plant-environment interactions but also prevents fusions between different plant organs and is therefore necessary for normal epidermal differentiation and organ formation.

Transgenic Arabidopsis plants expressing a fungal cutinase show alterations in the structure and properties of the cuticle and postgenital organ fusions

A major structural component of the cuticle of plants is cutin. Analysis of the function of cutin in vivo has been limited because no mutants with specific defects in cutin have been characterized. Therefore, transgenic Arabidopsis plants were generated that express and secrete a cutinase from Fusarium solani f sp pisi. Arabidopsis plants expressing the cutinase in the extracellular space showed an altered ultrastructure of the cuticle and an enhanced permeability of the cuticle to solutes. In addition, pollen could germinate on fully differentiated leaves of cutinase-expressing plants but not on control leaves. These differences coincided with strong postgenital organ fusions. The junctions of the fusions contained pectic polysaccharides. As fused organs grew apart from each other, organ deformations and protrusions of epidermal cells developed at positions with high mechanical stress. These results demonstrate that an intact cutin layer not only is important for plant-environment interactions but also prevents fusions between different plant organs and is therefore necessary for normal epidermal differentiation and organ formation.