ABSTRACT
A seed marks the transition between two developmental states; a plant is an embryo during seed formation, whereas it is a seedling after emergence from the seed. Two factors have been identified in Arabidopsis that play a role in establishment of repression of the embryonic state: PKL (PICKLE), which codes for a putative CHD3 chromatin remodeling factor, and gibberellin (GA), a plant growth regulator. Previous observations have also suggested that PKL mediates some aspects of GA responsiveness in the adult plant. To investigate possible mechanisms by which PKL and GA might act to repress the embryonic state, we further characterized the ability of PKL and GA to repress embryonic traits and reexamined the role of PKL in mediating GA-dependent responses. We found that PKL acts throughout the seedling to repress expression of embryonic traits. Although the ability of pkl seedlings to express embryonic traits is strongly induced by inhibiting GA biosynthesis, it is only marginally responsive to abscisic acid and SPY (SPINDLY), factors that have previously been demonstrated to inhibit GA-dependent responses during germination. We also observed that pkl plants exhibit the phenotypic hallmarks of a mutation in a positive regulator of a GA response pathway including reduced GA responsiveness and increased synthesis of bioactive GAs. These observations indicate that PKL may mediate a subset of GA-dependent responses during shoot development.
Subject(s)
Arabidopsis Proteins/genetics , Arabidopsis/embryology , Arabidopsis/genetics , Genes, Plant , Arabidopsis/drug effects , Base Sequence , DNA Helicases , DNA, Plant/genetics , Gene Expression Regulation, Developmental , Gene Expression Regulation, Plant , Germination , Gibberellins/biosynthesis , Gibberellins/pharmacology , Phenotype , Plants, Genetically Modified , Repressor Proteins/geneticsABSTRACT
From an enhancer trap screen for genes expressed in Arabidopsis embryos, we identified a gene expressed from the octant stage onward in the boundary between the two presumptive cotyledons and in a variety of postembryonic organ and meristem boundaries. This gene, CUP-SHAPED COTYLEDON3 (CUC3), encodes a putative NAC-domain transcription factor that is homologous with CUC1 and CUC2. Analysis of a CUC3 hypomorph and a putative cuc3 null mutant indicates that CUC3 function is partially redundant with that of CUC1 and CUC2 in the establishment of the cotyledon boundary and the shoot meristem, thus revealing an even higher degree of redundancy in this class of genes than was thought previously. The CUC3 expression pattern, the cuc3 phenotypes, and CUC3 expression in a series of shoot meristem mutants and transgenes suggest a primary role for CUC3 in the establishment of boundaries that contain cells with low proliferation and/or differentiation rates. The CUC-mediated establishment of such boundaries may be essential for the initiation of shoot meristems.
Subject(s)
Arabidopsis Proteins/genetics , Arabidopsis/genetics , Meristem/genetics , Plant Shoots/genetics , Transcription Factors/genetics , Arabidopsis/growth & development , Arabidopsis/metabolism , Arabidopsis Proteins/metabolism , Base Sequence , Cloning, Molecular , DNA, Plant/chemistry , DNA, Plant/genetics , Gene Expression Regulation, Developmental , Gene Expression Regulation, Plant , Glucuronidase/genetics , Glucuronidase/metabolism , Homeodomain Proteins/genetics , Homeodomain Proteins/metabolism , In Situ Hybridization , Meristem/growth & development , Meristem/metabolism , Molecular Sequence Data , Mutation , Phenotype , Phylogeny , Plant Shoots/growth & development , Plant Shoots/metabolism , Seeds/genetics , Seeds/growth & development , Seeds/metabolism , Sequence Analysis, DNA , Transcription Factors/metabolismABSTRACT
Zygotic embryos of three Arabidopsis thaliana (L.) Heynh. mutants lacking an embryonic shoot apical meristem (SAM), shoot meristemless (stm), wuschel (wus) and zwille/pinhead (zll/pnh) were used as explants to establish embryogenic cell cultures. Somatic embryos of all three mutants showed the same mutant phenotypes as their zygotic equivalents. These results provide genetic evidence that the developmental program of somatic and zygotic embryos is indistinguishable. They also suggest that a functional SAM is not required for somatic embryogenic cell formation in Arabidopsis.
