Growth and development of Brassica genotypes differing in endogenous gibberellin content. I. Leaf and reproductive development

Comparative Transcriptome Analysis of Early- and Late-Bolting Traits in Chinese Cabbage (Brassica rapa)

Chinese cabbage is one of the most important and widely consumed vegetables in China. The developmental transition from the vegetative to reproductive phase is a crucial process in the life cycle of flowering plants. In spring-sown Chinese cabbage, late bolting is desirable over early bolting. In this study, we analyzed double haploid (DH) lines of late bolting (“Y410-1” and “SY2004”) heading Chinese cabbage (Brassica rapa var. pekinensis) and early-bolting Chinese cabbage (“CX14-1”) (B. rapa ssp. chinensis var. parachinensis) by comparative transcriptome profiling using the Illumina RNA-seq platform. We assembled 721.49 million clean high-quality paired-end reads into 47,363 transcripts and 47,363 genes, including 3,144 novel unigenes. There were 12,932, 4,732, and 4,732 differentially expressed genes (DEGs) in pairwise comparisons of Y410-1 vs. CX14-1, SY2004 vs. CX14-1, and Y410-1 vs. SY2004, respectively. The RNA-seq results were confirmed by reverse transcription quantitative real-time PCR (RT-qPCR). A Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of DEGs revealed significant enrichment for plant hormone and signal transduction as well as starch and sucrose metabolism pathways. Among DEGs related to plant hormone and signal transduction, six unigenes encoding the indole-3-acetic acid-induced protein ARG7 (BraA02g009130), auxin-responsive protein SAUR41 (BraA09g058230), serine/threonine-protein kinase BSK11 (BraA07g032960), auxin-induced protein 15A (BraA10g019860), and abscisic acid receptor PYR1 (BraA08g012630 and BraA01g009450), were upregulated in both late bolting Chinese cabbage lines (Y410-1 and SY2004) and were identified as putative candidates for the trait. These results improve our understanding of the molecular mechanisms underlying flowering in Chinese cabbage and provide a foundation for studies of this key trait in related species.

The ABA-mediated switch between submersed and emersed life-styles in aquatic macrophytes

Hydrophytes comprise aquatic macrophytes from various taxa that are able to sustain and to complete their lifecycle in a flooded environment. Their ancestors, however, underwent adaptive processes to withstand drought on land and became partially or completely independent of water for sexual reproduction. Interestingly, the step backwards into the high-density aquatic medium happened independently several times in numerous plant taxa. For flowering plants, this submersed life-style is especially difficult as they need to erect their floral organs above the water surface to be pollinated. Moreover, fresh-water plants evolved the adaptive mechanism of heterophylly, which enabled them to switch between a submersed and an emersed leaf morphology. The plant hormone abscisic acid (ABA) is a key factor of heterophylly induction in aquatic plants and is a major switch between a submersed and emersed life. The mechanisms of ABA signal perception and transduction appear to be conserved throughout the evolution of basal plants to angiosperms and from terrestrial to aquatic plants. This review summarizes the interplay of environmental factors that act through ABA to orchestrate adaptation of plants to their aquatic environment.

De novo variation in life-history traits and responses to growth conditions of resynthesized polyploid Brassica napus (Brassicaceae)

Variation that arises in generations immediately following polyploidization may be important for the establishment, adaptation, and persistence of new polyploid species. We previously showed divergence for flowering time among lines from a resynthesized Brassica napus allopolyploid lineage derived from a cross of diploid B. rapa and B. oleracea. In this study, we more fully assess phenotypic differentiation of lines from the previously studied lineage and of lines derived from an additional resynthesized B. napus lineage. Nine polyploid lines and their diploid parents were grown under four growth conditions and measured for eight life-history traits. Polyploid lines within a lineage were expected to be genetically identical because they were derived from individual, chromosome-doubled amphihaploid plants. However, significant differences were found among lines within lineages for every phenotypic trait measured and in response to different growth conditions (genotype by environment interactions). When phenotypes of each polyploid line for each trait in each environment were compared with their diploid progenitors, approximately 30% were like one or the other parent, 50% were intermediate, and 20% were transgressive. Our results demonstrate extensive de novo variation in new polyploid lineages. Such changes could contribute to the evolutionary potential in naturally occurring polyploids.

Growth and development of Brassica genotypes differing in endogenous gibberellin content. II. Gibberellin content, growth analyses and cell size

Three rapid cycling Brassica rapa genotypes were grown in greenhouse conditions to investigate the possible relationships between endogenous gibberellin (GA) content and shoot growth. Endogenous GA(1) GA(3) and GA(20) were extracted from stem samples harvested at 3 weekly intervals and analyzed by gas chromatography-mass spectrometry with selected ion monitoring, using [(2) H(2) ]-GA(1) and [(2) H(2) ]-GA(20) as quantitative internal standards. During the first 2 weeks, GA levels of the dwarf, rosette (ros), averaged 36% of levels in normal plants (on a per stem basis). Levels in the tall mutant, elongated internode (ein), were consistently higher, averaging 305% of levels in normal plants. Differences in shoot height across the genotypes resulted from varying internode length which resulted from epidermal cell length and number being increased in ein and decreased in ros relative to the normal genotype. The exogenous application of GA(3) to normal plants increased cell length while the application of paclobutrazol (PP333), a triazole plant growth retardant, reduced cell size. Thus, exogenous GA manipulations mimicked the influence of the mutant genes ros and ein. The dwarf, ros, had reduced shoot dry weights and relative growth rates compared to the other genotypes. Total dry weights were similar in ein and the normal genotype but stem weights were increased in ein, compensating for decreased leaf weights. Thus, the gibberellin-deficiency of ros resulted in generally reduced shoot growth. The overproduction of endogenous GA by ein did not result in enhanced shoot growth but rather a specific enhancement of internode elongation and stem growth at the expense of leaf size.