An Arabidopsis Cotyledon-Specific Albino Locus: a Possible Role in 16S rRNA Maturation

Abstract

We report here the isolation and characterization of a cotyledon-specific albino locus of Arabidopsis, WHITE COTYLEDONS (WCO). This recessive mutation in the WCO locus, located on the top of Chromosome 1, results in albino cotyledons but green true leaves. An accumulation profile of chlorophylls and ultrastructure of chloroplasts indicate that WCO is necessary for development of functional chloroplasts in cotyledons but is dispensable in true leaves. This was further supported by the fact that the mutants request feeding of sucrose for their survival at the early seedling stage where true leaves have not emerged, but the mutants which have developed true leaves are able to grow autotrophically without sucrose supplementation. The wco mutants accumulate low levels of chloroplast mRNA encoding photosynthesis-related proteins and have a specific defect in 16S rRNA maturation in a cotyledon-specific manner. Although wco mutants exhibited abnormal chloroplasts and chloroplast gene expression in cotyledons, nuclear genes for photosynthetic components are expressed at similar levels to those found in wild-type siblings. This lack of suppression of the nuclear genes is not due to a defect in the signaling of the so-called "plastid factor" to the nucleus since normal suppression of the nuclear genes was observed in response to the photo-oxidative damage due to norflurazon application.

Modified Clp Protease Complex in the ClpP3 Null Mutant and Consequences for Chloroplast Development and Function in Arabidopsis

“…Once this block is broken, by the addition of either Glc or Suc to the growth medium, cotyledons unfold and true leaves are formed. These CLP alleles do not have white cotyledons, as observed for a subset of plastid mutants, the locus white cotyledon1 (Yamamoto et al, 2000), the cyo1 stromal elongation factor G (SCO1; Albrecht et al, 2006;Ruppel and Hangarter, 2007), or the thylakoid protein disulfide isomerase CYO1/SCO2 (Shimada et al, 2007;Albrecht et al, 2008;Tanz et al, 2012; for review, see Pogson and Albrecht, 2011). These sco mutants are not affected in chloroplast development during embryogenesis in the developing silique.…”

Mutations in SUPPRESSOR OF VARIEGATION1, a Factor Required for Normal Chloroplast Translation, Suppress var2-Mediated Leaf Variegation in Arabidopsis

“…Other factors that affect chloroplast rRNA maturation are defined by a handful of mutants that accumulate rRNA intermediates. These include the following: (1) maize high chlorophyll fluorescence7 (Barkan, 1993), maize rnc1 (Watkins et al, 2007), and Arabidopsis white cotyledon (Yamamoto et al, 2000), all of which accumulate primarily 16S rRNA precursors; (2) Chlamydomonas ac20, which is defective in 23S rRNA maturation (Holloway and Herrin, 1998); (3) Arabidopsis dal (for dag-like, from the differentiation and greening mutant of snapdragon [Antirrhinum majus]) (Chatterjee et al, 1996), which accumulates 16S and 23S precursor rRNAs (Babiychuk et al, 1997;Bisanz et al, 2003); and (4) tomato dcl (for defective chloroplasts and leaves), in which 4.5S rRNA processing is defective (Bellaoui et al, 2003); 4.5S rRNA processing is also impaired in Arabidopsis mutants with downregulated DCL gene expression (Bellaoui and Gruissem, 2004). (C) Determination of the T-DNA insertion site in ClpR1/SVR2.…”

The Cytosolic Kinases STY8, STY17, and STY46 Are Involved in Chloroplast Differentiation in Arabidopsis

“…Several mutants have been identified, with distinct phenotypes in chloroplast biogenesis restricted to either cotyledons or true leaves. In a mutant of the FtsH complex, var2, and in var3, pigment deficiencies are confined to true leaves only (Chen et al, 2000;Naested et al, 2004), whereas in other mutants, such as snowy cotyledon1 and snowy cotyledon2 (Albrecht et al, 2006(Albrecht et al, , 2008, white cotyledon (Yamamoto et al, 2000), and cyo1 (Shimada et al, 2007), chloroplast formation is solely affected in cotyledons. All of these genes encode for chloroplast-localized proteins, which exert their function within the organelle and are involved in the reorganization of the plastid on the transcriptional or protein level.…”