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Summary: The genetic control underlying natural variation in lignin content and composition in trees is not fully understood. We performed a systems genetic analysis to uncover the genetic regulation of lignin biosynthesis in a natural 'SwAsp' population of aspen (Populus tremula) trees.We analyzed gene expression by RNA sequencing (RNA‐seq) in differentiating xylem tissues, and lignin content and composition using Pyrolysis‐GC‐MS in mature wood of 268 trees from 99 genotypes.Abundant variation was observed for lignin content and composition, and genome‐wide association study identified proteins in the pentose phosphate pathway and arabinogalactan protein glycosylation among the top‐ranked genes that are associated with these traits. Variation in gene expression and the associated genetic polymorphism was revealed through the identification of 312 705 local and 292 003 distant expression quantitative trait loci (eQTL). A co‐expression network analysis suggested modularization of lignin biosynthesis and novel functions for the lignin‐biosynthetic CINNAMYL ALCOHOL DEHYDROGENASE 2 and CAFFEOYL‐CoA O‐METHYLTRANSFERASE 3. PHENYLALANINE AMMONIA LYASE 3 was co‐expressed with HOMEOBOX PROTEIN 5 (HB5), and the role of HB5 in stimulating lignification was demonstrated in transgenic trees.The systems genetic approach allowed linking natural variation in lignin biosynthesis to trees´ responses to external cues such as mechanical stimulus and nutrient availability. [ABSTRACT FROM AUTHOR]

SUMMARY: Scots pine (Pinus sylvestris L.) is one of the most widespread and economically important conifer species in the world. Applications like genomic selection and association studies, which could help accelerate breeding cycles, are challenging in Scots pine because of its large and repetitive genome. For this reason, genotyping tools for conifer species, and in particular for Scots pine, are commonly based on transcribed regions of the genome. In this article, we present the Axiom Psyl50K array, the first single nucleotide polymorphism (SNP) genotyping array for Scots pine based on whole‐genome resequencing, that represents both genic and intergenic regions. This array was designed following a two‐step procedure: first, 192 trees were sequenced, and a 430K SNP screening array was constructed. Then, 480 samples, including haploid megagametophytes, full‐sib family trios, breeding population, and range‐wide individuals from across Eurasia were genotyped with the screening array. The best 50K SNPs were selected based on quality, replicability, distribution across the draft genome assembly, balance between genic and intergenic regions, and genotype–environment and genotype–phenotype associations. Of the final 49 877 probes tiled in the array, 20 372 (40.84%) occur inside gene models, while the rest lie in intergenic regions. We also show that the Psyl50K array can yield enough high‐confidence SNPs for genetic studies in pine species from North America and Eurasia. This new genotyping tool will be a valuable resource for high‐throughput fundamental and applied research of Scots pine and other pine species. Significance Statement: In this paper, we present the first high‐throughput single nucleotide polymorphism genotyping array for a pine species developed from whole‐genome resequencing, and thus spanning genic as well as intergenic regions. This array was developed for Scots pine and successfully tested in six other pine species from North America and Eurasia, being useful for fundamental and applied studies in the fields of population genetics, evolution, genomic selection, and breeding. [ABSTRACT FROM AUTHOR]

In temperate and boreal regions, perennial plants adapt their annual growth cycle to the change of seasons. In natural forests, juvenile seedlings usually display longer growth seasons compared to adult trees to ensure their establishment and survival under canopy shade. However, how trees adjust their annual growth according to their age is not known. In this study, we show that age-dependent seasonal growth cessation is genetically controlled and found that the miR156-SPL3/5 module, a key regulon of vegetative phase change (VPC), also triggers age-dependent growth cessation in Populus trees. We show that miR156 promotes shoot elongation during vegetative growth, and its targets SPL3/5s function in the same pathway but as repressors. We find that the miR156-SPL3/5s regulon controls growth cessation in both leaves and shoot apices and through multiple pathways, but with a different mechanism compared to how the miR156-SPL regulon controls VPC in annual plants. Taken together, our results reveal an age-dependent genetic network in mediating seasonal growth cessation, a key phenological process in the climate adaptation of perennial trees. [ABSTRACT FROM AUTHOR]

LEAFY (LFY) early-acting genes are candidates for upstream regulators of flower-specific ABC genes, but it is difficult to determine the directness of interactions between LFY and ABC genes, as LFY affects the flower meristem identity. It is now shown that the role of LFY in flower-meristem initiation is separated for its later role in activation of homeotic genes. A genetic framework for the patterning of flowers is thus able to be proposed.

Among the genes that control the transition to flowering in Arabidopsis is a large group whose inactivation causes a delay in flowering. It has been difficult to establish different pathways in which the flowering-time genes might act, because mutants with lesions in these genes have very similar phenotypes. Among the putative targets of the flowering-time genes is another group of genes, which control the identity of individual meristems. Overexpression of one of the meristem-identity genes, LEAFY, can cause the precocious generation of flowers and thus early flowering. We have exploited the opposite phenotypes seen in late-flowering mutants and LEAFY overexpressers to clarify the genetic interactions between flowering-time genes and LEAFY. According to epistatic relationships, we can define one class of flowering-time genes that affects primarily the response to LEAFY activity, and another class of genes that affects primarily the transcriptional induction of LEAFY. These observations allow us to expand previously proposed models for the genetic control of flowering time.

The expression of the LEAFY (LFY) gene, a flower-meristem-identity gene, of Arabidopsis induces flowering in transgenic Arabidopsis and aspen plants by converting the lateral and apical shoots into flowers. The phenotypic expression of this gene is suppressed if there is a mutation in the APETALA1 gene or the plant is exposed to short days. The phenotype of these transgenic plants is similar to plants containing mutation in the TERMINAL FLOWER gene.

The room temperature thermal and electrical conductivity of monolithic carbon aerogels were investigated. The results showed that both the solid thermal conductivity and the electrical conductivity scaled with the density in the range between 60 and 650 kg m(super -3). Both conductivities exhibited scaling exponents of 1.5. In addition, a thermal conductivity of 0. 029 W m(super -1)K(super -1) in air and 0.018 W m(super -1)K(super -1) after evacuation was observed when the density was 82 kg m(super -3).