Nucleotide diversity of vernalization and flowering‐time‐related genes in a germplasm collection of meadow fescue (Festuca pratensis Huds. syn. Lolium pratense (Huds.) Darbysh.)

In plant species, control of flowering time is an important factor for adaptation to local natural environments. The Vrn1, CO, FT1 and CK2α genes are key components in the flowering‐specific signaling pathway of grass species. Meadow fescue is an agronomically important forage grass species, which is naturally distributed across Europe and Western Asia. In this study, meadow fescue flowering‐time‐related genes were resequenced to assess nucleotide diversity in European and Western Asian subpopulations. Identified sequence polymorphisms were then converted into PCR‐based molecular genetic markers, and a meadow fescue germplasm collection was genotyped to investigate global allelic variation. Lower nucleotide diversities were observed for the Vrn1 and CO orthologs, while relatively higher values were observed for the FT1 and casein kinase II α‐subunit (CK2α) orthologs. The nucleotide diversity for FT1 orthologs in the Western Asian subpopulation was significantly higher than those of the European subpopulation. Similarly, significant differences in nucleotide diversity for the remaining genes were observed between several combinations of subpopulation. The global allele distribution pattern was consistent with observed level of nucleotide diversity. These results suggested that the degree of purifying selection acting on the genes differs according to geographical location. As previously shown for model plant species, functional specificities of flowering‐time‐related genes may also vary according to environmental conditions.     

The MADS-box gene DAL1 is a potential mediator of the juvenile-to-adult transition in Norway spruce (Picea abies)

Progression through the plant life cycle involves change in many essential features, most notably in the capacity to reproduce. The transition from a juvenile vegetative and non-reproductive to an adult reproductive phase is gradual and can take many years; in the conifer Norway spruce, Picea abies, typically 20-25 years. We present a detailed analysis of the activities of three regulatory genes with potential roles in this transition in Norway spruce: DAL1, a MADS-box gene related to the AGL6 group of genes from angiosperms, and the two LEAFY-related genes PaLFY and PaNLY. DAL1 activity is initiated in the shoots of juvenile trees at an age of 3-5 years, and then increases with age, whereas both LFY genes are active throughout the juvenile phase. The activity of DAL1 further shows a spatial pattern along the stem of the tree that parallels a similar gradient in physiological and morphological features associated with maturation to the adult phase. Constitutive expression of DAL1 in transgenic Arabidopsis plants caused a dramatic attenuation of both juvenile and adult growth phases; flowers forming immediately after the embryonic phase of development in severely affected plants. Taken together, our results support the notion that DAL1 may have a regulatory role in the juvenile-to-adult transition in Norway spruce.     

Defining subdomains of the K domain important for protein–protein interactions of plant MADS proteins

The MADS proteins APETALA3 (AP3), PISTILLATA (PI), SEPALLATAI (SEPI), SEP2, SEP3, AGAMOUS, and APETALA are required for proper floral organ identity in Arabidopsis flowers. All of these floral MADS proteins conserve two domains: the MADS domain that mediates DNA binding and dimerization, and the K domain that mediates protein protein interaction. The K domain is postulated to form a several amphipathic c-helices referred to as K1, K2, and K3. The K1 and K2 helicies are located entirely within the K domain while the K3 helix spans the K domain-C domain boundary. Here we report on our studies on the interactions of the B class MADS proteins AP3 and PI with the E class MADS proteins SEP1, SEP2, and SEP3. A comparative analysis of mutants in the K domain reveals that the subdomains mediating the PI/AP3 interaction are different from the subdomains mediating the PI/SEP3 (or PI/SEP1) interaction. The strong PI/SEP3 (or PI/SEP1) interaction requires K2, part of K3, and the interhelical region between K1 and K2. By contrast, K1, K2 and the region between K1 and K2 are important for strong AP3/PI interaction. Most of the K3 helix does not appear to be important for either the PI/AP3 or the PI/SEP3 (or PI/SEP1) interaction. Conserved hydrophobic positions are most important for the strength of both PI/AP3 and PI/SEP3 dimerization, though ionic and/or polar interactions appear to play a secondary role.     

A MADS domain gene involved in the transition to flowering in Arabidopsis

Flowering time in many plants is triggered by environmental factors that lead to uniform flowering in plant populations, ensuring higher reproductive success. So far, several genes have been identified that are involved in flowering time control. AGL20 (AGAMOUS LIKE 20) is a MADS domain gene from Arabidopsis that is activated in shoot apical meristems during the transition to flowering. By transposon tagging we have identified late flowering agl20 mutants, showing that AGL20 is involved in flowering time control. In previously described late flowering mutants of the long-day and constitutive pathways of floral induction the expression of AGL20 is down-regulated, demonstrating that AGL20 acts downstream to the mutated genes. Moreover, we can show that AGL20 is also regulated by the gibberellin (GA) pathway, indicating that AGL20 integrates signals of different pathways of floral induction and might be a central component for the induction of flowering. In addition, the constitutive expression of AGL20 in Arabidopsis is sufficient for photoperiod independent flowering and the over-expression of the orthologous gene from mustard, MADSA, in the classical short-day tobacco Maryland Mammoth bypasses the strict photoperiodic control of flowering.     

CaMADS1, a MADS box gene expressed in the carpel of hazelnut

Hazelnut (Corylus avellana L.) is a species of economic interest that shows a peculiar floral biology. Unlike most of the angiosperms, which produce ovules during floral development such that they are ready for pollen at anthesis, hazelnut ovary development is delayed and triggered by compatible pollination. In order to elucidate the mechanisms regulating this unusual process and the role of the MADS box genes in ovary development, a cDNA library from pollinated styles of hazelnut was screened with a mixture of MADS box genes from different plant species. CaMADS1 (Corylus avellana MADS box), a floral-specific MADS box gene, was isolated, and characterized as belonging to the sub-family of the AGAMOUS genes. Northern blot, RT-PCR analyses and in situ hybridization experiments show a precise correlation between ovary development and CaMADS1 expression, indicating a role of this MADS box gene in the processes of floral organogenesis.