DNA binding with One Finger (DOF) transcription factors are involved in multiple aspects of plant growth and development but their precise roles in abiotic stress tolerance are largely unknown. Here we report a group of five tomato DOF genes, homologous to Arabidopsis Cycling DOF Factors (CDFs), that function as transcriptional regulators involved in responses to drought and salt stress and flowering-time control in a gene-specific manner. SlCDF1-5 are nuclear proteins that display specific binding with different affinities to canonical DNA target sequences and present diverse transcriptional activation capacities in vivo. SlCDF1-5 genes exhibited distinct diurnal expression patterns and were differentially induced in response to osmotic, salt, heat, and low-temperature stresses. Arabidopsis plants overexpressing SlCDF1 or SlCDF3 showed increased drought and salt tolerance. In addition, the expression of various stress-responsive genes, such as COR15, RD29A, and RD10, were differentially activated in the overexpressing lines. Interestingly, overexpression in Arabidopsis of SlCDF3 but not SlCDF1 promotes late flowering through modulation of the expression of flowering control genes such as CO and FT. Overall, our data connect SlCDFs to undescribed functions related to abiotic stress tolerance and flowering time through the regulation of specific target genes and an increase in particular metabolites.

The phenylpropanoid metabolic pathway provides a wide variety of essential compounds for plants. Together with sinapate esters, in Brassicaceae species, flavonoids play an important role in protecting plants against UV irradiation. In this work we have characterized Arabidopsis thaliana AtMYB7, the closest homolog of AtMYB4 and AtMYB32, described as repressors of different branches of phenylpropanoid metabolism. The characterization of atmyb7 plants revealed an induction of several genes involved in flavonol biosynthesis and an increased amount of these compounds. In addition, AtMYB7 gene expression is repressed by AtMYB4. As a consequence, the atmyb4 mutant plants present a reduction of flavonol contents, indicating once more that AtMYB7 represses flavonol biosynthesis. Our results also show that AtMYB7 gene expression is induced by salt stress. Induction assays indicated that AtMYB7 represses several genes of the flavonoid pathway, DFR and UGT being early targets of this transcription factor. The results obtained indicate that AtMYB7 is a repressor of flavonol biosynthesis and also led us to propose AtMYB4 and AtMYB7 as part of the regulatory mechanism controlling the balance of the main A. thaliana UV-sunscreens.

TERMINAL FLOWER 1 (TFL1) is a key regulator of Arabidopsis plant architecture that responds to developmental and environmental signals to control flowering time and the fate of shoot meristems. TFL1 expression is dynamic, being found in all shoot meristems, but not in floral meristems, with the level and distribution changing throughout development. Using a variety of experimental approaches we have analysed the TFL1 promoter to elucidate its functional structure. TFL1 expression is based on distinct cis-regulatory regions, the most important being located 3′ of the coding sequence. Our results indicate that TFL1 expression in the shoot apical versus lateral inflorescence meristems is controlled through distinct cis-regulatory elements, suggesting that different signals control expression in these meristem types. Moreover, we identified a cis-regulatory region necessary for TFL1 expression in the vegetative shoot and required for a wild-type flowering time, supporting that TFL1 expression in the vegetative meristem controls flowering time. Our study provides a model for the functional organisation of TFL1 cis-regulatory regions, contributing to our understanding of how developmental pathways are integrated at the genomic level of a key regulator to control plant architecture.

The results identify AGO1 as a repressor of TFL1 expression. Moreover, they reveal a novel role for AGO1 in inflorescence development, controlling the production of coflorescences. AGO1 seems to play this role through regulating TFL1 expression.

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[Abstract] Tomato is one of the most important horticultural crops worldwide, and is cultivated in semi-arid regions in which soil and groundwater salinity is an increasing limitation to yield. The assessment of the responses of new cultivars to salt and the comparisons among cultivars and wild species are of great interest in tomato breeding. This assay provides a reproducible and reliable method for screening tomato responses to NaCl salinity under hydroponic conditions in growth chambers. Although NaCl is the most commonly used salt in salinity studies, other salts such as Na 2 SO 4 , MgCl 2 or MgSO 4 , usually found in saline soils, can also be assayed (Nebauer et al., 2013). Plants can be maintained for 30-45 days under the described conditions, although significant effects on growth can be observed after 10 days, depending on the salt and concentration used. Materials and Reagents