The Spanish Ministry of Science and Innovation (PID2019-109925GB-I00 to D.A.) and the European Union (H2020-MSCA-IF-2016-746396 to A.S.-M.). We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

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Regulation of della Proteins by Post-translational Modifications

The blue light receptor CRY1 interacts with GID1 and DELLA proteins to repress GA signaling during photomorphogenesis in Arabidopsis

Flowering is one of the most critical developmental transitions in plants’ life. The irreversible change from the vegetative to the reproductive stage is strictly controlled to ensure the progeny’s success. In Arabidopsis thaliana, seven flowering genetic pathways have been described under specific growth conditions. However, the evidence condensed here suggest that these pathways are tightly interconnected in a complex multilevel regulatory network. In this review, we pursue an integrative approach emphasizing the molecular interactions among the flowering regulatory network components. We also consider that the same regulatory network prevents or induces flowering phase change in response to internal cues modulated by environmental signals. In this sense, we describe how during the vegetative phase of development it is essential to prevent the expression of flowering promoting genes until they are required. Then, we mention flowering regulation under suboptimal growing temperatures, such as those in autumn and winter. We next expose the requirement of endogenous signals in flowering, and finally, the acceleration of this transition by long-day photoperiod and temperature rise signals allowing A. thaliana to bloom in spring and summer seasons. With this approach, we aim to provide an initial systemic view to help the reader integrate this complex developmental process.

Beyond the Genetic Pathways, Flowering Regulation Complexity in Arabidopsis thaliana

Gibberellin (GA) 2-oxidases play an important role in the GA catabolic pathway through 2β-hydroxylation. There are two classes of GA2oxs, i.e., a larger class of C19-GA2oxs and a smaller class of C20-GA2oxs. In this study, the gene encoding a GA 2-oxidase of rice, Oryza sativa GA 2-oxidase 5 (OsGA2ox5), was cloned and characterized. BLASTP analysis showed that OsGA2ox5 belongs to the C20-GA2oxs subfamily, a subfamily of GA2oxs acting on C20-GAs (GA12, GA53). Subcellular localization of OsGA2ox5-YFP in transiently transformed onion epidermal cells revealed the presence of this protein in both of the nucleus and cytoplasm. Real-time PCR analysis, along with GUS staining, revealed that OsGA2ox5 is expressed in the roots, culms, leaves, sheaths and panicles of rice. Rice plants overexpressing OsGA2ox5 exhibited dominant dwarf and GA-deficient phenotypes, with shorter stems and later development of reproductive organs than the wild type. The dwarfism phenotype was partially rescued by the application of exogenous GA3 at a concentration of 10 µM. Ectopic expression of OsGA2ox5 cDNA in Arabidopsis resulted in a similar phenotype. Real-time PCR assays revealed that both GA synthesis-related genes and GA signaling genes were expressed at higher levels in transgenic rice plants than in wild-type rice; OsGA3ox1, which encodes a key enzyme in the last step of the bioactive GAs synthesis pathway, was highly expressed in transgenic rice. The roots of OsGA2ox5-ox plants exhibited increased starch granule accumulation and gravity responses, revealing a role for GA in root starch granule development and gravity responses. Furthermore, rice and Arabidopsis plants overexpressing OsGA2ox5 were more resistant to high-salinity stress than wild-type plants. These results suggest that OsGA2ox5 plays important roles in GAs homeostasis, development, gravity responses and stress tolerance in rice.

OsGA2ox5, a Gibberellin Metabolism Enzyme, Is Involved in Plant Growth, the Root Gravity Response and Salt Stress

DELLA proteins are master growth regulators that repress responses to a group of plant growth hormones called gibberellins (GAs). Manipulation of DELLA function and signaling was instrumental in the development of high-yielding crop varieties that saved millions from starvation during the "Green Revolution." Despite decades of extensive research, it is still unclear how DELLA function and signaling mechanisms evolved within the land plant lineage. Here, we review current knowledge on DELLA protein function with reference to structure, posttranslational modifications, downstream transcriptional targets, and protein-protein interactions. Furthermore, we discuss older and recent findings regarding the evolution of DELLA signaling within the land plant lineage, with an emphasis on bryophytes, and identify future avenues of research that would enable us to shed more light on the evolution of DELLA signaling. Unraveling how DELLA function and signaling mechanisms have evolved could enable us to engineer better crops in an attempt to contribute to mitigating the effects of global warming and achieving global food security.

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Evolution of DELLA function and signaling in land plants

FLAVIN-BINDING KELCH REPEAT F-BOX 1 (FKF1) encodes an F-box protein that regulates photoperiod flowering in Arabidopsis under long-day conditions (LDs). Gibberellin (GA) is also important for regulating flowering under LDs. However, how FKF1 and the GA pathway work in concert in regulating flowering is not fully understood. Here, we showed that the mutation of FKF1 could cause accumulation of DELLA proteins, which are crucial repressors in GA signaling pathway, thereby reducing plant sensitivity to GA in flowering. Both in vitro and in vivo biochemical analyses demonstrated that FKF1 directly interacted with DELLA proteins. Furthermore, we showed that FKF1 promoted ubiquitination and degradation of DELLA proteins. Analysis of genetic data revealed that FKF1 acted partially through DELLAs to regulate flowering under LDs. In addition, DELLAs exerted a negative feedback on FKF1 expression. Collectively, these findings demonstrate that FKF1 promotes flowering partially by negatively regulating DELLA protein stability under LDs, and suggesting a potential mechanism linking the FKF1 to the GA signaling DELLA proteins.

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FKF1 F-box protein promotes flowering in part by negatively regulating DELLA protein stability under long-day photoperiod in Arabidopsis

Phenotype and TMT-based quantitative proteomics analysis of Brassica napus reveals new insight into chlorophyll synthesis and chloroplast structure

Plant height is one of the important agronomic traits of crops. Gibberellins (GAs) play an important role in the regulation of plant height. Gibberellin 2-oxidase (GA2ox) inactivates active GAs or their precursors and plays a key role in the catabolism of GAs. Here, we isolated and characterized a fragment from rapeseed (Brassica napus L.), designated BnGA2ox2, that is highly expressed in the silique and flower. Overexpression of BnGA2ox2 in Arabidopsis resulted in GA-deficient phenotypes, including a short hypocotyl, reduced plant height, increased chlorophyll and anthocyanin accumulation, late flowering, and partial sterility. Similarly, when BnGA2ox2 was overexpressed in rapeseed, the transgenic plants had a dwarf phenotype with dark-green leaves and increased chlorophyll and anthocyanin accumulation. In addition, similar dwarf phenotypes were observed in Arabidopsis overexpressing AtGA2ox2. Genetic analysis showed that the atga2ox2 mutation could partially rescue the phenotype of BnGA2ox2 transgenic Arabidopsis plant, indicating that BnGA2ox2 and AtGA2ox2 have conserved functions in vegetative plant growth and stem elongation. These results suggest that BnGA2ox2 regulates stem elongation and chlorophyll and anthocyanin accumulation in rapeseed and Arabidopsis. Therefore, BnGA2ox2 is a new candidate gene for breeding dwarf varieties of rapeseed.

Overexpression of BnGA2ox2, a rapeseed gibberellin 2-oxidase, causes dwarfism and increased chlorophyll and anthocyanin accumulation in Arabidopsis and rapeseed

Plant height is an important plant characteristic closely related to yield performance of many crops. Reasonable reduction of plant height of crops is beneficial for improving yield and enhancing lodging resistance. In the present study, we described the Brassica napus dwarf mutant bnd2 that was isolated using ethyl methanesulfonate (EMS) mutagenesis. Compared to wild type (WT), bnd2 exhibited reduced height and shorter hypocotyl and petiole leaves. By crossing the bnd2 mutant with the WT strain, we found that the ratio of the mutant to the WT in the F2 population was close to 1:3, indicating that bnd2 is a recessive mutation of a single locus. Following bulked segregant analysis (BSA) by resequencing, BND2 was found to be located in the 13.77–18.08 Mb interval of chromosome A08, with a length of 4.31 Mb. After fine mapping with single nucleotide polymorphism (SNP) and insertion/deletion (InDel) markers, the gene was narrowed to a 140-Kb interval ranging from 15.62 Mb to 15.76 Mb. According to reference genome annotation, there were 27 genes in the interval, of which BnaA08g20960D had an SNP type variation in the intron between the mutant and its parent, which may be the candidate gene corresponding to BND2. The hybrid line derived from a cross between the mutant bnd2 and the commercial cultivar L329 had similar plant height but higher grain yield compared to the commercial cultivar, suggesting that the allele bnd2 is beneficial for hybrid breeding of lodging resistant and high yield rapeseed. In this study, we identified a novel dwarf mutant of rapeseed with a new locus, which may be useful for functional analyses of genetic mechanisms of plant architecture and grain yield in rapeseed.

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Piao Yang

Papers

FKF1 F-box protein promotes flowering in part by negatively regulating DELLA protein stability under long-day photoperiod in Arabidopsis

Phenotype and TMT-based quantitative proteomics analysis of Brassica napus reveals new insight into chlorophyll synthesis and chloroplast structure

Overexpression of BnGA2ox2, a rapeseed gibberellin 2-oxidase, causes dwarfism and increased chlorophyll and anthocyanin accumulation in Arabidopsis and rapeseed

Characterization and fine mapping of a new dwarf mutant in Brassica napus