Characterisation of a new allele ofpale cress and its role in greening inArabidopsis thaliana

Abstract

A recessive mutant with white leaves was identified in a screen of a population of T-DNA-tagged Arabidopsis thaliana plants. The mutation is lethal, but plants develop almost to maturity under sterile conditions. The white areas in leaves are devoid of developed chloroplasts, but the plants frequently develop green sectors which contain green chloroplasts. Molecular characterisation of the affected gene revealed that the mutant is allelic to pale cress (pac), a recently described mutation, and was therefore named pac-2. Sequencing of cDNAs and the genomic region revealed several noteworthy features of this genetic locus. In pac-2 the T-DNA had inserted in the region of the promoter and abolished transcription of the PAC gene completely. Cytokinin induced greening in mature, white homozygous pac-2 plants, and therefore is likely to be responsible for the greening observed in callus and shoots induced on roots from such plants. However, the PAC transcript was found to be absent in both white leaves and green callus. Thus, since cytokinin induced greening in the absence of PAC RNA this plant hormone appears to be able to bypass PAC function.

The Peroxisome Deficient Arabidopsis Mutant sse1 Exhibits Impaired Fatty Acid Synthesis

“…Even in leaf tissues where photosynthesis provides most of the ATP and reducing power for fatty acid synthesis, exogenous sugar could serve as an alternative resource when photosynthesis is abolished. This is demonstrated by the fact that Arabidopsis albino mutants could grow to fairly normal size in tissue culture in the presence of exogenous sugar (Grevelding et al, 1996;Motohashi et al, 2001). Based on these rationales, we think it is unlikely that the dramatic reduction of oil content in sse1 is due solely to lack of photosynthesis.…”

Leaf-variegated mutations and their responsible genes in Arabidopsis thaliana.

“…For example, pale cress ( pac ) is an albino mutant and lethal unless growing together with a carbon source (Reiter et al, 1994). When grown on a sucrose-containing medium, it shows green spots on a chlorotic leaf, perhaps because chloroplast development is partially rescued by supplementing a carbon source (Grevelding et al, 1996). On the other hand, the mutant called cab underexpressed ( cue ) has been isolated (Li et al, 1995) based on the reduced expression of a reporter gene driven by a light-dependent promoter from CAB gene (encoding a core protein of light harvesting complex II).…”

Arabidopsis Variegation Mutants

“…Cytokinin is also able to induce greening in pac2 (Grevelding et al, 1996) and atd2 (van der Graaff, 1997), two nuclear gene-induced variegations (see Table 1). Therefore, further insight into how cytokinins control plastid biogenesis might lend insight into im compensating activities.…”

“…Two T-DNA-tagged alleles of the pale cress (pac) mutant have been isolated (Reiter et al, 1994;Grevelding et al, 1996). One allele is pale-green (pac1) and the other has green/white variegated leaves (pac2).…”