The steroidal hormone brassinosteroids (BRs) play important roles in plant growth and development. Genetic, genomic and proteomic studies in Arabidopsis have identified major BR signaling components and elucidated the signal transduction pathway from the cell surface receptor kinase BRI1 to the BES1/BZR1 family of transcription factors. BRs interact with other plant hormones in coordinating gene expression and plant growth and development. In this review, we provide an update on the latest progress in characterizing the BR signaling network and discuss its interactions with other hormone pathways in determining yield component traits and in regulating stress responses.

This study investigated the differences in microbial community abundance, composition, and diversity throughout the depth profiles in soils collected from corn and soybean fields in Iowa (United States) using 16S rRNA amplicon sequencing. The results revealed decreased richness and diversity in microbial communities at increasing soil depth. Soil microbial community composition differed due to crop type only in the top 60 cm and due to location only in the top 90 cm. While the relative abundance of most phyla decreased in deep soils, the relative abundance of the phylum Proteobacteria increased and dominated agricultural soils below the depth of 90 cm. Although soil depth was the most important factor shaping microbial communities, edaphic factors, including soil organic matter, soil bulk density, and the length of time that deep soils were saturated with water, were all significant factors explaining the variation in soil microbial community composition. Soil organic matter showed the highest correlation with the exponential decrease in bacterial abundance with depth. A greater understanding of how soil depth influences the diversity and composition of soil microbial communities is vital for guiding sampling approaches in agricultural soils where plant roots extend beyond the upper soil profile. In the long term, a greater knowledge of the influence of depth on microbial communities should contribute to new strategies that enhance the sustainability of soil, which is a precious resource for food security. IMPORTANCE Determining how microbial properties change across different soils and within the soil depth profile will be potentially beneficial to understanding the long-term processes that are involved in the health of agricultural ecosystems. Most literature on soil microbes has been restricted to the easily accessible surface soils. However, deep soils are important in soil formation, carbon sequestration, and providing nutrients and water for plants. In the most productive agricultural systems in the United States where soybean and corn are grown, crop plant roots extend into the deeper regions of soils (>100 cm), but little is known about the taxonomic diversity or the factors that shape deep-soil microbial communities. The findings reported here highlight the importance of soil depth in shaping microbial communities, provide new information about edaphic factors that influence the deep-soil communities, and reveal more detailed information on taxa that exist in deep agricultural soils.

Soil pH is a major factor shaping bulk soil microbial communities. However, it is unclear whether the belowground microbial habitats shaped by plants (e.g. rhizosphere and root endosphere) are also affected by soil pH. We investigated this question by comparing the microbial communities associated with plants growing in neutral and strongly alkaline soils in the Sandhills, which is the largest sand dune complex in the northern hemisphere. Bulk soil, rhizosphere and root endosphere DNA were extracted from multiple plant species and analyzed using 16S rRNA amplicon sequencing. Results showed that rhizosphere, root endosphere and bulk soil microbiomes were different in the contrasting soil pH ranges. The strongest impact of plant species on the belowground microbiomes was in alkaline soils, suggesting a greater selective effect under alkali stress. Evaluation of soil chemical components showed that in addition to soil pH, cation exchange capacity also had a strong impact on shaping bulk soil microbial communities. This study extends our knowledge regarding the importance of pH to microbial ecology showing that root endosphere and rhizosphere microbial communities were also influenced by this soil component, and highlights the important role that plants play particularly in shaping the belowground microbiomes in alkaline soils.

17 The determination of how microbial community structure changes within the soil profile, 18 will be beneficial to understanding the long-term health of agricultural soil ecosystems 19 and will provide a first step towards elucidating how deep soil microbial communities 20 contribute to carbon sequestration. This study aimed to investigate the differences in the 21 microbial community abundance, composition and diversity throughout from the surface 22 layers down to deep soils in corn and soybean fields in Iowa, USA. We used 16S rRNA 23 amplicon sequencing of soil samples to characterize the change in microbial community 24 structure. Our results revealed decreased richness and diversity in bacterial community 25 structure with increasing soil depth. We also observed distinct distribution patterns of 26 bacterial community composition along soil profiles. Soil and root data at different 27 depths enabled us to demonstrate that the soil organic matter, soil bulk density and 28 plant water availability were all significant factors in explaining the variation in soil 29 microbial community composition. Our findings provide valuable insights in the changes 30 in microbial community structure to depths of 180 cm in one of the most productive 31 agricultural regions in the world. This knowledge will be important for future 32 management and productivity of agroecosystems in the face of increasing demand for 33 food and climate change. 34 35 36

Autumn dormancy in alfalfa (Medicago sativa) is associated with agronomically important traits including regrowth rate, maturity, and winter survival. Historical recurrent selection experiments have been able to manipulate the dormancy response. We hypothesized that artificial selection for dormancy phenotypes in these experiments had altered allele frequencies of dormancy-related genes. Here, we follow this hypothesis and analyze allele frequency changes using genome-wide polymorphisms in the pre- and postselection populations from one historical selection experiment. We screened the nondormant cultivar CUF 101 and populations developed by three cycles of recurrent phenotypic selection for taller and shorter plants in autumn with markers derived from genotyping-by-sequencing (GBS). We validated the robustness of our GBS-derived allele frequency estimates using an empirical approach. Our results suggest that selection mapping is a powerful means of identifying genomic regions associated with traits, and that it can be exploited to provide regions on which to focus further mapping and cloning projects.