Project description:The timing of reproductive development determines spike architecture and thus yield in temperate grasses such as barley (Hordeum vulgare L.). Reproductive development in barley is controlled by the photoperiod response gene Ppd-H1 which accelerates flowering time under long-day (LD) conditions. A natural mutation in Ppd-H1 prevalent in spring barley causes a reduced photoperiod response, and thus, late flowering under LD. However, it is not very well understood how LD and Ppd-H1 control pre-anthesis development, and thus spike architecture and yield in barley. We performed a detailed morphological analysis of the pre-anthesis development in the spring barley cultivar Scarlett and its wild barley derived introgression line S42-IL107, carrying the photoperiod responsive Ppd-H1 allele. Characterization of shoot apex development in these genotypes indicated that floral transition and initiation of floral primordia occurred under LD (16h light/ 8h dark) and short day (SD, 8h light/ 16h dark) conditions, while inflorescence and seed development strictly required LDs. Additionally, a fast photoperiod response in the presence of the dominant Ppd-H1 allele promoted floret fertility under LDs. To characterize the effects of the photoperiod and allelic variation at Ppd-H1 on gene expression during pre-anthesis development we performed RNA sequencing of leaves and developing main shoot apices during the vegetative phase and early stages of inflorescence development in Scarlett and S42-IL107 grown under SD and LD conditions. Main shoot apices of both genotypes were sampled at defined developmental stages, i.e. Waddington stage W0.5, W1.0, W2.0 and W3.5, respectively. Leaf samples were harvested from plants before (W1.0) and after floral transition (W2.0). We identified genes that were specifically regulated at floral transition independent of day-length and Ppd-H1 and thus may serve as markers for the staging of floral transition. Furthermore, we identified transcripts differentially expressed between photoperiods and between genotypes in leaves and in shoot apices. This set of transcripts might act as candidates downstream of Ppd-H1 and are correlated with the promotion of shoot apex development and higher floret fertility under LD and in the presence of the photoperiod responsive Ppd-H1 allele.
Project description:Ramie is an important industrial fiber crop, and the fiber yield and its related traits are the most valuable traits in ramie production. However, the genetic basis for these traits is still poorly understood. Herein, a high-density genetic map with 1085 markers spanning 2,118.8 cM was constructed using a population derived from two parents, cultivated ramie Zhongsizhu 1 (ZSZ1) and its wild progenitor B. nivea var. tenacissima (BNT). The fiber yield (FY) and its four related traits—stem diameter (SD) and length (SL), stem bark weight (BW) and thickness (BT)—were performed for quantitative trait locus (QTL) analysis, resulting in eight, six, six, three, and ten QTLs for SD, SL, BW, BD and FY traits, respectively. These 33 QTLs were mapped into 11 genomic regions, thus forming 11 QTL clusters; there were 11 QTLs identified their beneficial alleles from the wild species BNT. Interestingly, all QTLs in Cluster 8 and Cluster 10 displayed overdominance, indicating that these two regions were likely heterotic loci. In addition, there were five fiber yield-related genes identified to undergo positive selection in previous study, and they were found to locate into the genomic region near to the QTLs of this study. The genetic dissection for FY and its related traits improved our understanding to the genetic basis of these traits, as well to their domestication in ramie. The identification of many QTLs and the discovery of beneficial alleles from wild species provided a basis for the improvement of yield traits in ramie breeding.