Repressing the expression of the SUCROSE NONFERMENTING-1-RELATED PROTEIN KINASE gene in pea embryo causes pleiotropic defects of maturation similar to an abscisic acid-insensitive phenotype

The classic role of SUCROSE NONFERMENTING-1 (Snf1)-like kinases in eukaryotes is to adapt metabolism to environmental conditions such as nutrition, energy, and stress. During pea (Pisum sativum) seed maturation, developmental programs of growing embryos are adjusted to changing physiological and metabolic conditions. To understand regulation of the switch from cell proliferation to differentiation, SUCROSE NONFERMENTING-1-RELATED PROTEIN KINASE (SnRK1) was antisense repressed in pea seeds. Transgenic seeds show maturation defects, reduced conversion of sucrose into storage products, lower globulin content, frequently altered cotyledon surface, shape, and symmetry, as well as occasional precocious germination. Gene expression analysis of embryos using macroarrays of 5,548 seed-specific genes revealed 183 differentially expressed genes in two clusters, either delayed down-regulated or delayed up-regulated during transition. Delayed down-regulated genes are related to mitotic activity, gibberellic acid/brassinosteroid synthesis, stress response, and Ca2+ signal transduction. This specifies a developmentally younger status and conditional stress. Higher gene expression related to respiration/gluconeogenesis/fermentation is consistent with a role of SnRK1 in repressing energy-consuming processes in maturing cotyledons under low oxygen/energy availability. Delayed up-regulated genes are mainly related to storage protein synthesis and stress tolerance. Most of the phenotype resembles abscisic acid (ABA) insensitivity and may be explained by reduced Abi-3 expression. This may cause a reduction in ABA functions and/or a disconnection between metabolic and ABA signals, suggesting that SnRK1 is a mediator of ABA functions during pea seed maturation. SnRK1 repression also impairs gene expression associated with differentiation, independent from ABA functions, like regulation and signaling of developmental events, chromatin reorganization, cell wall synthesis, biosynthetic activity of plastids, and regulated proteolysis.     

Stepwise origin and functional diversification of the AFL subfamily B3 genes during land plant evolution

The AFL genes (ABI3/VP1, FUS3 and LEC2) belong to the plant-specific B3 superfamily, playing important roles in regulating seed development and maturation. It is unclear, however, whether these genes appeared at the same time as the origin of seed plants and if all these genes are necessary and sufficient for seed development for all seed plants. By conducting a genome-wide comparative analysis of the putative AFL genes in various plant species, we found that the ABI3 homologous genes existed in all land plant genomes, but the FUS3 homologous were present only in seed plant genomes and the LEC2-like sequences only in dicot genomes. Phylogenetic analysis indicated that the AFL genes had undergone successive rounds of gene duplication and subsequent diversification during land plant evolution, resulting in the stepwise origin of the ABI3, FUS3 and LEC2 genes. Comparison of gene structure of the AFL genes revealed a trend of decreasing in the number of conserved domains from ABI3 to FUS3 and LEC2.     

Genomic DNA sequences of two new genes for new storage protein glutelin in rice.

A new cDNA and two genomic genes encoding the rice storage protein glutelin were isolated and sequenced. The nucleotide sequence of one gene (GluA-3) was completely identical with that of the new cDNA identified here, and the other (GluA-4) was a pseudogene. These glutelin genes were closely related to each other, and belonged to the subfamily A containing the type I (GluA-1) and II (GluA-2) glutelin genes. The Northern blot analysis, using synthetic oligonucleotide specific to the GluA-3 gene as a probe, showed that this gene was expressed earlier than other glutelin genes during seed maturation.     

COP9: a new genetic locus involved in light-regulated development and gene expression in arabidopsis.

We report here the identification and characterization of a new Arabidopsis light-regulatory locus, COP9, mutation that leads to a constitutive photomorphogenic phenotype. Dark-grown cop9 seedlings exhibit many morphological characteristics of light-grown seedlings, including short hypocotyls and open and enlarged cotyledons with cell-type and chloroplast differentiation. Furthermore, the cop9 mutation leads to high-level expression of light-inducible genes in the absence of light, probably by altering the promoter activities of these genes. These properties imply that the mutation in the COP9 locus uncouples the light/dark signals from morphogenesis and light-regulated gene expression. In addition, light-grown cop9 mutants are severely dwarfed and are unable to reach maturation and flowering. This adult-lethal phenotype indicates that the COP9 locus also plays a critical role for normal development of the light-grown plant. Similar to cop1 mutants, but not det1, the cop9 mutants show (1) no effect on the phytochrome control of seed germination and (2) deficiency in the dark-adaptive change of expression of light-regulated genes. Our results suggest that the cop9 and cop1 mutations result in the same range of phenotypes and therefore COP9 and COP1 loci may encode closely related components in the same regulatory pathway.