Flowering in Arabidopsis is promoted via several interacting pathways. A photoperiod-dependent pathway relays signals from photoreceptors to a transcription factor gene, CONSTANS (CO), which activates downstream meristem identity genes such as LEAFY (LFY). FT, together with LFY, promotes flowering and is positively regulated by CO. Loss of FT causes delay in flowering, whereas overexpression of FT results in precocious flowering independent of CO or photoperiod. FT acts in part downstream of CO and mediates signals for flowering in an antagonistic manner with its homologous gene, TERMINAL FLOWER1 (TFL1).

ZPT2-related proteins that have two canonical Cys-2/His-2-type zinc-finger motifs in their molecules are members of a family of plant transcription factors. To characterize the role of this type of protein, we analyzed the function of Arabidopsis L. Heynh. genes encoding four different ZPT2-related proteins (AZF1, AZF2, AZF3, and STZ). Gel-shift analysis showed that the AZFs and STZ bind to A(G/C)T repeats within an EP2 sequence, known as a target sequence of some petunia (Petunia hybrida) ZPT2 proteins. Transient expression analysis using synthetic green fluorescent protein fusion genes indicated that the AZFs and STZ are preferentially localized to the nucleus. These four ZPT2-related proteins were shown to act as transcriptional repressors that down-regulate the transactivation activity of other transcription factors. RNA gel-blot analysis showed that expression of AZF2 and STZ was strongly induced by dehydration, high-salt and cold stresses, and abscisic acid treatment. Histochemical analysis of b-glucuronidase activities driven by the AZF2 or STZ promoters revealed that both genes are induced in leaves rather than roots of rosette plants by the stresses. Transgenic Arabidopsis overexpressing STZ showed growth retardation and tolerance to drought stress. These results suggest that AZF2 and STZ function as transcriptional repressors to increase stress tolerance following growth retardation.Drought, high salinity, and low temperature are adverse environmental conditions that limit the growth of plants. Plants respond and adapt to these stresses in order to survive. These stresses induce various biochemical and physiological changes, including growth inhibition, to acquire stress tolerance. A number of genes have been described that respond to stresses at the transcriptional level (Ingram and

Postembryonic development of plants depends on the activity of apical meristems established during embryogenesis. The shoot apical meristem (SAM) and the root apical meristem (RAM) have similar but distinct cellular organization. Arabidopsis FASCIATA1 (FAS1) and FAS2 genes maintain the cellular and functional organization of both SAM and RAM, and FAS gene products are subunits of the Arabidopsis counterpart of chromatin assembly factor-1 (CAF-1). fas mutants are defective in maintenance of the expression states of WUSCHEL (WUS) in SAM and SCARECROW (SCR) in RAM. We suggest that CAF-1 plays a critical role in the organization of SAM and RAM during postembryonic development by facilitating stable maintenance of gene expression states.

SUMMARYColletotrichum higginsianum is a fungal pathogen that infects a wide variety of cruciferous plants, causing important crop losses. We have used map-based cloning and natural variation analysis of 19 Arabidopsis ecotypes to identify a dominant resistance locus against C. higginsianum. This locus named RCH2 (for recognition of C. higginsianum) maps in an extensive cluster of disease-resistance loci known as MRC-J in the Arabidopsis ecotype Ws-0. By analyzing natural variations within the MRC-J region, we found that alleles of RRS1 (resistance to Ralstonia solanacearum 1) from susceptible ecotypes contain single nucleotide polymorphisms that may affect the encoded protein. Consistent with this finding, two susceptible mutants, rrs1-1 and rrs1-2, were identified by screening a T-DNA-tagged mutant library for the loss of resistance to C. higginsianum. The screening identified an additional susceptible mutant (rps4-21) that has a 5-bp deletion in the neighboring gene, RPS4-Ws, which is a well-characterized R gene that provides resistance to Pseudomonas syringae pv. tomato strain DC3000 expressing avrRps4 (Pst-avrRps4). The rps4-21/rrs1-1 double mutant exhibited similar levels of susceptibility to C. higginsianum as the single mutants. We also found that both RRS1 and RPS4 are required for resistance to R. solanacearum and Pst-avrRps4. Thus, RPS4-Ws and RRS1-Ws function as a dual resistance gene system that prevents infection by three distinct pathogens.