GATA transcription factors are a group of DNA binding proteins broadly distributed in eukaryotes. The GATA factors DNA binding domain is a class IV zinc finger motif in the form CX₂CX_17–20CX₂C followed by a basic region. In plants, GATA DNA motifs have been implicated in light-dependent and nitrate-dependent control of transcription. Herein, we show that the Arabidopsis and the rice (Oryza sativa) genomes present 29 and 28 loci, respectively, that encode for putative GATA factors. A phylogenetic analysis of the 57 GATA factors encoding genes, as well as the study of their intron-exon structure, indicates the existence of seven subfamilies of GATA genes. Some of these subfamilies are represented in both species but others are exclusive for one of them. In addition to the GATA zinc finger motif, polypeptides of the different subfamilies are characterized by the presence of additional domains such as an acidic domain, a CCT (CONSTANS, CO-like, and TOC1) domain, or a transposase-like domain also found in FAR1 and FHY3. Subfamily VI comprises genes that encode putative bi-zinc finger polypeptides, also found in metazoan and fungi, and a tri-zinc finger protein which has not been previously reported in eukaryotes. The phylogeny of the GATA zinc finger motif, excluding flanking regions, evidenced the existence of four classes of GATA zinc fingers, three of them containing 18 residues in the zinc finger loop and one containing a 20-residue loop. Our results support multiple models of evolution of the GATA gene family in plants including gene duplication and exon shuffling.

The target of rapamycin (TOR) is a conserved Ser/Thr kinase that controls cell growth by activating an array of anabolic processes including protein synthesis, transcription, and ribosome biogenesis, and by inhibiting catabolic processes such as mRNA degradation and autophagy. Control of autophagy by TOR occurs primarily at the induction step, and involves activation of the ATG1 kinase, a conserved component of the autophagic machinery. A substantial number of genes participating in autophagy have been originally identified in yeast. Most of these genes have mammalian homologues and many have apparent homologues in plants, indicating that autophagy is conserved among eukaryotes. The recent identification of TOR as a key element in cell growth control in plants and algae opens the way for future studies to investigate whether this signaling pathway may also control autophagy in photosynthetic organisms.

The regulatory circuits that control nitrogen metabolism are relatively well known in several bacterial model groups. However, much less is understood about how the nitrogen status of the cell is perceived in vivo. In cyanobacteria, the transcription factor NtcA is required for regulation (activation or repression) of an extensive number of genes involved in nitrogen metabolism. In contrast, how NtcA activity is regulated is largely unknown. Assimilation of ammonium by most microorganisms occurs through the sequential action of two enzymes: glutamine synthetase (GS) and glutamate synthase. Interestingly, regulation of the expression of NtcA-dependent genes in the cyanobacteriumSynechocystis sp. PCC 6803 is altered in mutants with modified levels of GS activity. Two types of mutants were analyzed:glnA null mutants that lack GS type I and gifmutants unable to inactivate GS in the presence of ammonium. Changes in the intracellular pools of 19 different amino acids and the keto acid 2-oxoglutarate were recorded in wild-type and mutant strains under different nitrogen conditions. Our data strongly indicate that the nitrogen status in cyanobacteria is perceived as changes in the intracellular 2-oxoglutarate pool.

Summary: One of the mechanisms involved in chromatin remodelling is so‐called ‘histone replacement’. An example of such a mechanism is the substitution of canonical H2A histone by the histone variant H2A.Z. The ATP‐dependent chromatin remodelling complex SWR1 is responsible for this action in yeast. We have previously proposed the existence of an SWR1‐like complex in Arabidopsis by demonstrating genetic and physical interaction of the components SEF, ARP6 and PIE1, which are homologues of the yeast Swc6 and Arp6 proteins and the core ATPase Swr1, respectively. Here we show that histone variant H2A.Z, but not canonical H2A histone, interacts with PIE1. Plants mutated at loci HTA9 and HTA11 (two of the three Arabidopsis H2A.Z‐coding genes) displayed developmental abnormalities similar to those found in pie1, sef and arp6 plants, exemplified by an early‐flowering phenotype. Comparison of gene expression profiles revealed that 65% of the genes differentially regulated in hta9 hta11 plants were also mis‐regulated in pie1 plants. Detailed examination of the expression data indicated that the majority of mis‐regulated genes were related to salicylic acid‐dependent immunity. RT‐PCR and immunoblotting experiments confirmed constitutive expression of systemic acquired resistance (SAR) marker genes in pie1, hta9 hta11 and sef plants. Variations observed at the molecular level resulted in phenotypic alterations such as spontaneous cell death and enhanced resistance to the phytopathogenic bacteria Pseudomonas syringae pv. tomato. Thus, our results support the existence in Arabidopsis of an SWR1‐like chromatin remodelling complex that is functionally related to that described in yeast and human, and attribute to this complex a role in maintaining a repressive state of the SAR response.