Fatty acid breakdown in developing embryos of Brassica napus (L)

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Beat the weed : early bolting and flowering control research in full bloom

Peer reviewe

Development of new quantitative physiological and molecular breeding parameters based on the sugar beet vernalization intensity model.

Sugar-beet crops, Beta vulgaris spp. vulgaris (L), suffer from premature bolting and flowering as a consequence of prolonged exposure to cold conditions (vernalization). This reduces crop yield and quality and could be avoided if bolting-resistant varieties were available. Traditionally, development of bolting-resistant varieties has relied on selection against the annual growth habit associated with the bolting gene B. However, this has failed to deliver crops that can be reliably sown in early spring or grown over winter without the risk of bolting. New breeding targets and selection strategies are required and have become tractable with the recent development of the vernalization-intensity model. This model uses parameters for the intensity and duration of vernalization (vernalization hours) to predict bolting responses and discriminates between varieties by the minimum number of vernalization hours needed to induce bolting (vernalization requirement (VR)) and by the increase in bolting incidence for each extra vernalizing hour once the VR has been satisfied (bolting sensitivity (BS)). Since the vernalization-intensity model was developed from variety-assessment trials data, the present work sought to refine and test it through controlled environment (CE) experiments in which seven sugar-beet varieties were exposed to differing levels of accurately defined vernalization treatments and scored for bolting rates to determine their VR and BS values. The results confirmed and improved the model and showed that VR, not BS, has more potential for developing bolting resistant varieties. It was also observed that there exist in current varieties, the genetic potential to breed for higher VR. Further experiments assessed the correlation of attainment of VR with changes in gene expression and shoot apical meristem (SAM) morphology to identify potential markers for this trait. It was found that the time when VR is attained correlates with up-regulation of gibberellin biosynthetic genes and floral transcription factors in leaf and shoot apices; most prominently, GIBBERELLIN 20-OXIDASE 2 (BvGA20ox2) and FLOWERING LOCUS T 2 (BvFT2). To integrate the results with weather data, temperature records for the past 47 years from the Broom's Barn weather station were used to develop a tool for predicting accumulated vernalization hours based on sowing date. The results, together with data from the CE experiments, were used to establish VR-breeding targets for bolting-resistant varieties for spring- and autumn-sown sugar-beet crops. The present paper shows that integration of weather, VR and genetic data provide useful tools to aid both cultivation and breeding selection. For growers, it provides a weather data tool to assist with the selection of suitable sowing dates. For breeders, it provides the first identification of molecular genetic factors that correlate with VR and the physiological changes associated with vernalization responses in sugar beet. The results suggest that gene-expression profiles can be developed into tools for quantifying bolting resistance in beet, thereby providing a cost-effective, high-throughput and simple method for breeders to apply the vernalization-intensity model.Peer reviewe

Diurnal Changes in the Transcriptome Encoding Enzymes of Starch Metabolism Provide Evidence for Both Transcriptional and Posttranscriptional Regulation of Starch Metabolism in Arabidopsis Leaves

To gain insight into the synthesis and functions of enzymes of starch metabolism in leaves of Arabidopsis L. Heynth, Affymetrix microarrays were used to analyze the transcriptome throughout the diurnal cycle. Under the conditions employed, transitory leaf starch is degraded progressively during a 12-h dark period, and then accumulates during the following 12-h light period. Transcripts encoding enzymes of starch synthesis changed relatively little in amount over 24 h except for two starch synthases, granule bound starch synthase and starch synthase II, which increased appreciably during the transition from dark to light. The increase in RNA encoding granule-bound starch synthase may reflect the extensive destruction of starch granules in the dark. Transcripts encoding several enzymes putatively involved in starch breakdown showed a coordinated decline in the dark followed by rapid accumulation in the light. Despite marked changes in their transcript levels, the amounts of some enzymes of starch metabolism do not change appreciably through the diurnal cycle. Posttranscriptional regulation is essential in the maintenance of amounts of enzymes and the control of their activities in vivo. Even though the relationships between transcript levels, enzyme activity, and diurnal metabolism of starch metabolism are complex, the presence of some distinctive diurnal patterns of transcripts for enzymes known to be involved in starch metabolism facilitates the identification of other proteins that may participate in this process

Conservation and divergence of autonomous pathway genes in the flowering regulatory network of Beta vulgaris

The transition from vegetative growth to reproductive development is a complex process that requires an integrated response to multiple environmental cues and endogenous signals. In Arabidopsis thaliana, which has a facultative requirement for vernalization and long days, the genes of the autonomous pathway function as floral promoters by repressing the central repressor and vernalization-regulatory gene FLC. Environmental regulation by seasonal changes in daylength is under control of the photoperiod pathway and its key gene CO. The root and leaf crop species Beta vulgaris in the caryophyllid clade of core eudicots, which is only very distantly related to Arabidopsis, is an obligate long-day plant and includes forms with or without vernalization requirement. FLC and CO homologues with related functions in beet have been identified, but the presence of autonomous pathway genes which function in parallel to the vernalization and photoperiod pathways has not yet been reported. Here, this begins to be addressed by the identification and genetic mapping of full-length homologues of the RNA-regulatory gene FLK and the chromatin-regulatory genes FVE, LD, and LDL1. When overexpressed in A. thaliana, BvFLK accelerates bolting in the Col-0 background and fully complements the late-bolting phenotype of an flk mutant through repression of FLC. In contrast, complementation analysis of BvFVE1 and the presence of a putative paralogue in beet suggest evolutionary divergence of FVE homologues. It is further shown that BvFVE1, unlike FVE in Arabidopsis, is under circadian clock control. Together, the data provide first evidence for evolutionary conservation of components of the autonomous pathway in B. vulgaris, while also suggesting divergence or subfunctionalization of one gene. The results are likely to be of broader relevance because B. vulgaris expands the spectrum of evolutionarily diverse species which are subject to differential developmental and/or environmental regulation of floral transition.Peer reviewedFinal Published versio

The Role of a Pseudo-Response Regulator Gene in Life Cycle Adaptation and Domestication of Beet

Highlights: Map-based cloning of B in beet led to isolation of the PRR gene BvBTC1 BvBTC1 controls life cycle through differential regulation of the BvFT1/BvFT2 module BvBTC1 mediates floral transition in response to both long days and vernalization Beet domestication involved selection of a rare Bvbtc1 allele conferring bienniality Summary: Life cycle adaptation to latitudinal and seasonal variation in photoperiod and temperature is a major determinant of evolutionary success in flowering plants. Whereas the life cycle of the dicotyledonous model species Arabidopsis thaliana is controlled by two epistatic genes, FLOWERING LOCUS C and FRIGIDA [1,2,3], three unrelated loci (VERNALIZATION 1–3) determine the spring and winter habits of monocotyledonous plants such as temperate cereals [4,5,6]. In the core eudicot species Beta vulgaris, whose lineage diverged from that leading to Arabidopsis shortly after the monocot-dicot split 140 million years ago [7,8], the bolting locus B [9] is a master switch distinguishing annuals from biennials. Here, we isolated B and show that the pseudo-response regulator gene BOLTING TIME CONTROL 1 (BvBTC1), through regulation of the FLOWERING LOCUS T genes [10], is absolutely necessary for flowering and mediates the response to both long days and vernalization. Our results suggest that domestication of beets involved the selection of a rare partial loss-of-function BvBTC1 allele that imparts reduced sensitivity to photoperiod that is restored by vernalization, thus conferring bienniality, and illustrate how evolutionary plasticity at a key regulatory point can enable new life cycle strategies.Peer reviewe