FLD interacts with CO to affect both flowering time and floral initiation in Arabidopsis thaliana.

fld and co, both with significantly delayed flowering, are characterized as late-flowering mutations in Arabidopsis thaliana. Double mutants between fld-2 and co-3 were generated and the phenotypes characterized. Double mutants flower later than both single mutant parents, suggesting that there is an additive effect. In addition, the formation of flowers in double mutants was altered and showed a novel phenotype. Double mutant flowers contained a much longer stalk (pedicel). Sepals and petals were absent. Several leaf-like structures were produced in the position normally occupied by sepals and the organ numbers were reduced. The carpels were morphologically normal. The stamens produced were usually aborted in the early stage, thus, the flowers were sterile. The additive phenotype observed in double mutants provides evidence to support that these two genes, FLD and CO, are not only involved in rosette-to-inflorescence transition but also involved in the flower formation. This result also indicates that FLD and CO promote the reproductive program through two different pathways.     

A putative poplar PP2C-encoding gene negatively regulates drought and abscisic acid responses in transgenic Arabidopsis thaliana

Key message

Here we link for the first time a poplar gene with putative function in ABA signaling to the regulation of drought responses, providing a target for drought tolerance improvement in poplars.

Abstract

Populus species are valued for their fast growth and are cultivated widely. Many of the commonly used species and hybrids are, however, regarded as drought sensitive, which poses a problem for large-scale cultivation particularly in light of climate change-induced drought spells in areas of poplar growth. While many hundreds of drought-induced genes have been identified in Populus species, very little is known about the genes and the signaling process that leads to a drought response in these species. Based on sequence similarity, the poplar G059200 gene is a potential ortholog of AtPP2CA, an inhibitor of drought and abscisic acid (ABA) responses in Arabidopsis thaliana. To test if G059200 has a similar function, we generated transgenic A. thaliana plants overexpressing this gene. These transgenic lines exhibited reduced responses to exogenous ABA and reduced tolerance to osmotic stress. Finally, drought tolerance of plants was also significantly reduced. Taken together, these data provide evidences that G059200 acts as a negative regulator of ABA responses. The ability to negatively regulate drought stress responses suggests that G059200 may be targeted for drought tolerance breeding, for example, by identification of individuals harboring natural or induced loss-of-function alleles, or by RNA interference technology, to generate poplar plants with reduced activity of G059200.     

EMF genes interact with late-flowering genes in regulating floral initiation genes during shoot development in Arabidopsis thaliana

To investigate the mechanisms regulating the initiation of floral development in Arabidopsis, a construct containing beta-glucuronidase (GUS) gene driven by APETALA1 promoter (AP1::GUS) was introduced into emf fwa and emf ft double mutants. GUS activity was strongly detected on shoot meristem of emf1-1 single mutants harboring AP1::GUS construct just 5 d after germination. By contrast, GUS activity was undetectable on emf1-1 fwa-1, emf1-1 ft-1, emf2-1 fwa-1, emf2-3 fwa-1 and emf2-3 ft-1 double mutants harboring AP1::GUS construct 10 d after germination. GUS activity was only weakly detected on the apical meristem of 20-day-old emf1-1 fwa-1 and emf2-1 fwa-1 seedlings. During this time, only sessile leaves were produced. Further analysis indicated that AP1 was strongly expressed in 10-day-old emf1-1 and emf2-1 single mutants. Its expression was significantly reduced in all emf1-1 or emf2-1 late-flowering double mutants tested. Similar to AP1, the expression of LEAFY (LFY) was also high in emf1-1 and emf2-1 single mutants and reduced in emf1-1 or emf2-1 late-flowering double mutants. Our results indicate that the precocious expression of AP1 and LFY is dependent not only on the low EMF and FWA activities but also on the expression of most of the late-flowering genes such as FT, FCA, FE, CO and GI. These data also reveal that most late-flowering genes may function downstream of EMF or in pathways distinct from EMF to activate genes specified floral meristem identity during shoot maturation in Arabidopsis.     

Quantitative trait loci for floral morphology in Arabidopsis thaliana

A central question in biology is how genes control the expression of quantitative variation. We used statistical methods to estimate genetic variation in eight Arabidopsis thaliana floral characters (fresh flower mass, petal length, petal width, sepal length, sepal width, long stamen length, short stamen length, and pistil length) in a cosmopolitan sample of 15 ecotypes. In addition, we used genome-wide quantitative trait locus (QTL) mapping to evaluate the genetic basis of variation in these same traits in the Landsberg erecta x Columbia recombinant inbred line population. There was significant genetic variation for all traits in both the sample of naturally occurring ecotypes and in the Ler x Col recombinant inbred line population. In addition, broad-sense genetic correlations among the traits were positive and high. A composite interval mapping (CIM) analysis detected 18 significant QTL affecting at least one floral character. Eleven QTL were associated with several floral traits, supporting either pleiotropy or tight linkage as major determinants of flower morphological integration. We propose several candidate genes that may underlie these QTL on the basis of positional information and functional arguments. Genome-wide QTL mapping is a promising tool for the discovery of candidate genes controlling morphological development, the detection of novel phenotypic effects for known genes, and in generating a more complete understanding of the genetic basis of floral development.