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DELLA proteins BnaA6.RGA and BnaC7.RGA negatively regulate fatty acid biosynthesis by interacting with BnaLEC1s in Brassica napus.

ABSTRACT: Seed oil content (SOC) and fatty acid (FA) composition determine the quality and economic value of rapeseed (Brassica napus). Little is known about the role of gibberellic acid (GA) in regulating FA biosynthesis in B. napus. Here, we discovered that four BnaRGAs (B. napus REPRESSOR OF GA), encoding negative regulators of GA signalling, were suppressed during seed development. Compared to the wild type, SOC was reduced in gain-of-function mutants bnaa6.rga-D and ds-3, which also showed reduced oleic acid and increased linoleic acid contents. By contrast, the loss-of-function quadruple mutant bnarga displayed higher SOC during early seed development than the wild type, with increased oleic acid and reduced linoleic acid contents. Notably, only BnaA6.RGA and BnaC7.RGA physically interacted with two BnaLEC1s, which function as essential transcription factors in FA biosynthesis. The FA composition did not significantly differ between bnarga bnalec1 sextuple mutants and bnalec1, suggesting that BnaLEC1s are epistatic to BnaRGAs in the regulation of FA composition. Furthermore, BnaLEC1-induced activation of BnaABI3 expression was repressed by BnaA6.RGA, indicating that GA triggers the degradation of BnaRGAs to relieve their repression of BnaLEC1s, thus promoting the transcription of downstream genes to facilitate oil biosynthesis. Therefore, we uncovered a developmental stage-specific role of GA in regulating oil biosynthesis via the GA-BnaRGA-BnaLEC1 signalling cascade, providing a novel mechanistic understanding of how phytohormones regulate FA biosynthesis in seeds. BnaRGAs represent promising targets for oil crop improvement.

SUBMITTER: Yan G

PROVIDER: S-EPMC8486242 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundSubstance transport in higher land plants is mediated by vascular bundles, consisting of phloem and xylem strands that interconnect all plant organs. While the phloem mainly allocates photoassimilates, the role of the xylem is the transport of water and inorganic nutrients from roots to all aerial plant parts. Only recently it was noticed that in addition to mineral salts, xylem sap contains organic nutrients and even proteins. Although these proteins might have important impact on the performance of above-ground organs, only a few of them have been identified so far and their physiological functions are still unclear.ResultsWe used root-pressure xylem exudate, collected from cut Brassica napus stems, to extract total proteins. These protein preparations were then separated by high-resolution two-dimensional gel electrophoresis (2-DE). After individual tryptic digests of the most abundant coomassie-stained protein spots, partial peptide sequence information was deduced from tandem mass spectrometric (MS/MS) fragmentation spectra and subsequently used for protein identifications by database searches. This approach resulted in the identification of 69 proteins. These identifications include different proteins potentially involved in defence-related reactions and cell wall metabolism.ConclusionThis study provides a comprehensive overview of the most abundant proteins present in xylem sap of Brassica napus. A number of 69 proteins could be identified from which many previously were not known to be localized to this compartment in any other plant species. Since Brassica napus, a close relative of the fully sequenced model plant Arabidopsis thaliana, was used as the experimental system, our results provide a large number of candidate proteins for directed molecular and biochemical analyses of the physiological functions of the xylem under different environmental and developmental conditions. This approach will allow exploiting many of the already established functional genomic resources, like i.e. the large mutant collections, that are available for Arabidopsis.

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DELLA proteins BnaA6.RGA and BnaC7.RGA negatively regulate fatty acid biosynthesis by interacting with BnaLEC1s in Brassica napus.

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