Morphogenesis in higher plants originates from an undifferentiated group of cells, the meristem. After floral induction, the cells of a shoot apical meristem change in identity and form the inflorescence meristem that is characterized by a pattern of indeterminate growth and the production of flower meristems on its flanks. In Arabidopsis, these flower meristems are arranged in a spiral phyllotactic manner and are, unlike inflorescence meristems, determined. The flower meristems produce floral organ primordia in a precise number and pattern. Arabidopsis flowers are composed of four sepals in the first whorl, four petals in the second whorl, six stamens in the third whorl, and a pistil in the center of the flower. Inside the pistil, which is formed by the congenital fusion of two carpels, new primordia initiate and differentiate into the ovules. The initiation of primordia and the specification of their identity require a complex network of regulatory genes. A number of these regulatory genes has been isolated from Arabidopsis using molecular genetic approaches (for review, see Weigel 1995). Despite the identification of these genes and extensive studies in recent years, missing pieces in the puzzle limit our understanding of the interactions between the genes involved in flower ontogeny.The meristem identity genes LEAFY (LFY) (Weigel et al. 1992) and APETALA1 (AP1) (Mandel et al. 1992) from Arabidopsis are involved in the establishment of the floral meristem and mutations in these two genes cause a partial conversion of a floral meristem into an inflorescence meristem. Strong ap1 mutants produce highly branched, inflorescence-like flowers with ectopic secondary flowers in the axils of the first whorl organs (Irish and Sussex 1990; Mandel et al. 1992). LFY and AP1 act synergistically together with other floral meristem identity genes, among which the APETALA2 (AP2) gene (Jo- 4Corresponding author.

OsMADS13 is a rice MADS-box gene that is specifically expressed in developing ovules. The amino acid sequence of OsMADS13 shows 74% similarity to those of FLORAL BINDING PROTEIN 7 (FBP7) and FBP11, the products of two MADS-box genes that are necessary and sufficient to determine ovule identity in Petunia. To assess whether OsMADS13, the putative rice ortholog of FBP7 and FBP11, has an equivalent function, several analyses were performed. Ectopic expression of FBP7 and FBP11 in Petunia results in ectopic ovule formation on sepals and petals. Here we show that ectopic expression of OsMADS13 in rice and Arabidopsis does not result in the formation of such structures. Furthermore, ectopic expression of FBP7 and FBP11 in Arabidopsis also fails to induce ectopic ovule formation. To determine whether protein-protein interactions involving putative class D MADS-box proteins have been conserved, yeast two-hybrid assays were performed. These experiments resulted in the identification of three putative partners of OsMADS13, all of them encoded by AGL2-like genes. Interestingly the Petunia FBP7 protein also interacts with AGL2-like proteins. The evolutionary conservation of the MADS-box protein partners of these ovule-specific factors was confirmed by exchange experiments which showed that the protein partners of OsMADS13 interact with FBP7 and vice versa.

To increase both the yield potential and stability of crops, integrated breeding strategies are used that have mostly a direct genetic basis, but the utility of epigenetics to improve complex traits is unclear. A better understanding of the status of the epigenome and its contribution to agronomic performance would help in developing approaches to incorporate the epigenetic component of complex traits into breeding programs. Starting from isogenic canola (Brassica napus) lines, epilines were generated by selecting, repeatedly for three generations, for increased energy use efficiency and drought tolerance. These epilines had an enhanced energy use efficiency, drought tolerance, and nitrogen use efficiency. Transcriptome analysis of the epilines and a line selected for its energy use efficiency solely revealed common differentially expressed genes related to the onset of stress tolerance-regulating signaling events. Genes related to responses to salt, osmotic, abscisic acid, and drought treatments were specifically differentially expressed in the droughttolerant epilines. The status of the epigenome, scored as differential trimethylation of lysine-4 of histone 3, further supported the phenotype by targeting drought-responsive genes and facilitating the transcription of the differentially expressed genes. From these results, we conclude that the canola epigenome can be shaped by selection to increase energy use efficiency and stress tolerance. Hence, these findings warrant the further development of strategies to incorporate epigenetics into breeding.The need to improve crop yield in both quantity (yield potential) and stability (actual yield) to meet the increasing demand for food, feed, and plant-derived materials is a major challenge. Very different complementary technologies are used to optimize yield and to develop crops with increased resilience against adverse environmental growth conditions (Botella et al., 2008;Cattivelli et al., 2008; Jhaet al., 2014). Plant breeding programs are a basic component of this improvement process encompassing a wide range of technologies, such as exploration of the genetic potential by intraspecific and interspecific crosses, combination of genetic pools in hybrid breeding, mutational breeding, molecular breeding, and transgene technologies.Rather recently, epigenetics has been investigated as a potential breeding platform (Springer, 2013). Epigenetic variations or heritable changes in gene expression that are not linked to changes in the DNA sequence, but associated with differences in DNA methylation or histone modifications, provide an alternative source of phenotypic variability. A vast and growing number of studies implicate DNA methylation and histone modification in the modulation of gene expression in general, control of developmental transitions, and plant responses to biotic 1 This work was supported by the Agency for Innovation by Science and Technology (grant no. IWT100268), the Ghent University Special Research Fund (grant no. 01J11311), the European Training and...

Gene expression changes in plant roots infected by plant-parasitic cyst nematodes are involved in the formation of nematode feeding sites. We analyzed mRNA abundance changes within roots of Arabidopsis thaliana during the early compatible interaction with Heterodera schachtii, the sugarbeet cyst nematode. Approximately 1,600 root sections, each containing a single parasitic nematode and its feeding site, and 1,600 adjacent, nematode-free root sections were excised from aseptic A. thaliana cultures 3 to 4 days after inoculation with H. schachtii. These tissue samples were termed infected and uninfected, respectively. Preparasitic nematodes were added to the uninfected tissue sample to maintain the nematode to plant tissue proportion. mRNA extracted from these two tissue samples was subjected to differential display analysis. Thirty-six cDNA clones corresponding to mRNA species with different abundance between both tissue samples were isolated. Of these clones, 24 were of A. thaliana origin and 12 were from H. schachtii. Differential display data predicted that the A. thaliana cDNA clones corresponded to 13 transcripts that were more abundant in the infected root sections and 11 transcripts that were more abundant in the uninfected root sections. H. schachtii cDNA clones were predicted to correspond to four transcripts that were more abundant in parasitic nematodes and to eight transcripts that were more abundant in preparasitic nematodes. In situ hybridization experiments confirmed the mRNA abundance changes in A. thaliana roots predicted by the differential display analyses for two A. thaliana clones.