HighlightThis study reveals the ScFRK1 MAP kinase kinase kinase as a novel player in male and female gametophyte development, ultimately affecting pollen tube guidance and gametophyte to sporophyte communication.
BackgroundMembers of the plant MAP Kinases superfamily have been mostly studied in Arabidopsis thaliana and little is known in most other species. In Solanum chacoense, a wild species close to the common potato, it had been reported that members of a specific group in the MEKK subfamily, namely ScFRK1 and ScFRK2, are involved in male and female reproductive development. Apart from these two kinases, almost nothing is known about the roles of this peculiar family.MethodsMEKKs were identified using BLAST and hidden Markov model (HMM) to build profiles using the 21 MEKKs from A. thaliana. Following protein sequence alignments, the neighbor-joining method was used to reconstruct phylogenetic trees of the MEKK subfamily. Kinase subdomains sequence logos were generated with WebLogo in order to pinpoint FRK distinct motifs. Codon alignments of the FRKs kinase subdomains and maximum-likelihood phylogenetic trees were used in the codon substitution models of the codeml program in the PAML package to detect selective pressure between FRK groups.ResultsWith the recent progress in Next-Generation Sequencing technologies, the genomes and transcriptomes of numerous plant species have been recently sequenced, giving access to a vast amount of data. With the aim of finding all members of the MEKK subfamily members in plants, we screened the genomes of 15 species from different clades of the plant kingdom. Interestingly, the whole MEKK subfamily has significantly expanded throughout evolution, especially in solanaceous species. This holds true for members of the FRK class, which have also strongly expanded and diverged.ConclusionsExpansion and rapid evolution of the FRK class members in solanaceous species support the hypothesis that they have acquired new roles, mainly in male and female reproductive development.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2228-3) contains supplementary material, which is available to authorized users.
Background The Fertilization-related kinases (FRK) form a class that belongs to the MEKK subfamily of plant MAPKKKs. It was recently shown that FRK class kinases expanded during angiosperm evolution, reaching their maximum numbers in the lineage leading to solanaceous species and culminating in the Solanum genus where they account for more than 40% of the total MEKKs. The first members studied, ScFRK1 and ScFRK2 were shown to play a pivotal role in gametophyte development in the wild potato species Solanum chacoense. Results ScFRK3 is also involved in gametophyte development. ScFRK3 is expressed in developing pollen and young ovules, reaching its highest level immediately after meiosis and during the mitosis steps in both gametophytes. Hence, three independent lines of ScFRK3 RNAi mutant plants showed decreased number of seeds per fruit. We also observed an important number of degenerated embryo sac in mature ovary. Analysis of ovule development showed that most embryo sac did not enter mitosis I in Sc FRK3 RNAi mutant plants. Severe lethality was also observed during male gametophyte development, pollen being arrested before mitosis I, as observed in the female gametophyte. Obvious defects in vegetative organs were not observed, emphasizing the reproductive roles of the FRK class kinases. To isolate MAP kinases acting downstream of ScFRK3, a de novo S. chacoense transcriptome from male and female reproductive organs was assembled. Of the five ScMKKs and 16 ScMPKs retrieved, only the ScMKK3 interacted with ScFRK3, while only the ScMPK13 interacted with ScMKK3, leading to an apparent single three-tiered canonical MAP kinase cascade combination involving ScFRK3-ScMKK3-ScMPK13. Conclusions The ScFRK3 MAPKKK is involved in a signaling cascade that regulates both male and female gamete development, and most probably act upstream of ScMKK3 and ScMPK13. Electronic supplementary material The online version of this article (10.1186/s12870-019-1804-0) contains supplementary material, which is available to authorized users.
Followed by two previous conferences 20 and 40 years earlier, the Habitat III conference convened in Quito in 2016 to tackle global urban challenges. With cities experiencing ever-increasing levels of poverty, inequality, and vulnerability to climate change, Habitat's New Urban Agenda outlines its priorities for sustainable urban development considering current urban realities. This paper aims to assess the changing dynamics that have paved the road towards Habitat III and to evaluate the ongoing prospects for its effective policy implementation by analyzing: 1) the changing development paradigms that have informed the three meetings, and 2) the nature, adequacy and influence of Habitat policy frameworks. Our analysis elucidates the weak commitment of nations at framing and implementing policies that help advance past Habitat's agendas. This leads us to conclude that local governments may be better suited to promote just and sustainable development. Promising policymaking may occur if governments can intersect the principles of the New Urban Agenda with other global agendas, including the Sustainable Development Goals. Yet, it is relatively clear four years after Habitat III, that local commitment to these principles is not uniform either and that only certain world regions are actively participating in their implementation.
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