The Arabidopsis Cdk1/Cdk2 homolog CDKA;1 controls chromosome axis assembly during plant meiosis.

Meiosis is key to sexual reproduction and genetic diversity. Here, we show that the Arabidopsis cyclin-dependent kinase Cdk1/Cdk2 homolog CDKA;1 is an important regulator of meiosis needed for several aspects of meiosis such as chromosome synapsis. We identify the chromosome axis protein ASYNAPTIC 1 (ASY1), the Arabidopsis homolog of Hop1 (homolog pairing 1), essential for synaptonemal complex formation, as a target of CDKA;1. The phosphorylation of ASY1 is required for its recruitment to the chromosome axis via ASYNAPTIC 3 (ASY3), the Arabidopsis reductional division 1 (Red1) homolog, counteracting the disassembly activity of the AAA+ ATPase PACHYTENE CHECKPOINT 2 (PCH2). Furthermore, we have identified the closure motif in ASY1, typical for HORMA domain proteins, and provide evidence that the phosphorylation of ASY1 regulates the putative self-polymerization of ASY1 along the chromosome axis. Hence, the phosphorylation of ASY1 by CDKA;1 appears to be a two-pronged mechanism to initiate chromosome axis formation in meiosis.

The Arabidopsis Hop1 homolog ASY1 mediates cross-over assurance and interference.

The chromosome axis plays a crucial role in meiotic recombination. Here, we study the function of ASY1, the Arabidopsis homolog of the yeast chromosome axis-associated component Hop1. Specifically, we characterized cross-over (CO) distribution in female and male meiosis by deep sequencing of the progeny of an allelic series of asy1 mutants. Combining data from nearly 1,000 individual plants, we find that reduced ASY1 functionality leads to genomic instability and sometimes drastic genomic rearrangements. We further observed that COs are less frequent and appear in more distal chromosomal regions in plants with no or reduced ASY1 functionality, consistent with previous analyses. However, our sequencing approach revealed that the reduction in CO number is not as dramatic as suggested by cytological analyses. Analysis of double mutants of asy1 with mutants with three other CO factors, MUS81, MSH4, and MSH5, as well as the determination of foci number of the CO regulator MLH1 demonstrates that the majority of the COs in asy1, similar to the situation in the wildtype (WT), largely belong to the class I, which are subject to interference. However, these COs are redistributed in asy1 mutants and typically appear much closer than in the WT. Hence, ASY1 plays a key role in CO interference that spaces COs along a chromosome. Conversely, since a large proportion of chromosomes do not receive any CO, we conclude that CO assurance, the process that ensures the obligatory assignment of one CO per chromosome, is also affected in asy1 mutants.

Biotransformation of Phthalate Plasticizers and Bisphenol A by Marine-Derived, Freshwater, and Terrestrial Fungi.

Phthalate esters (PEs, Phthalates) are environmentally ubiquitous as a result of their extensive use as plasticizers and additives in diverse consumer products. Considerable concern relates to their reported xenoestrogenicity and consequently, microbial-based attenuation of environmental PE concentrations is of interest to combat harmful downstream effects. Fungal PE catabolism has received less attention than that by bacteria, and particularly fungi dwelling within aquatic environments remain largely overlooked in this respect. We have compared the biocatalytic and biosorptive removal rates of di-n-butyl phthalate (DBP) and diethyl phthalate (DEP), chosen to represent two environmentally prominent PEs of differing structure and hydrophobicity, by marine-, freshwater-, and terrestrial-derived fungal strains. Bisphenol A, both an extensively used plastic additive and prominent environmental xenoestrogen, was included as a reference compound due to its well-documented fungal degradation. Partial pathways of DBP metabolization by the ecophysiologically diverse asco- and basidiomycete strains tested were proposed with the help of UPLC-QTOF-MS analysis. Species specific biochemical reaction steps contributing to DBP metabolism were also observed. The involved reactions include initial cytochrome P450-dependent monohydroxylations of DBP with subsequent further oxidation of related metabolites, de-esterification via either hydrolytic cleavage or cytochrome P450-dependent oxidative O-dealkylation, transesterification, and demethylation steps - finally yielding phthalic acid as a central intermediate in all pathways. Due to the involvement of ecophysiologically and phylogenetically diverse filamentous and yeast-like fungi native to marine, freshwater, and terrestrial habitats the results of this study outline an environmentally ubiquitous pathway for the biocatalytic breakdown of plastic additives. Beyond previous research into fungal PE metabolism which emphasizes hydrolytic de-esterification as the primary catabolic step, a prominent role of cytochrome P450 monooxygenase-catalyzed reactions is established.