14-3-3 Gene of Zostera Japonica ZjGRF1 Participates in Gibberellin Signaling Pathway

Background Zostera japonica (Z. japonica) is a unique seagrass species in Asia, which has important ecological value. Gibberellin is an important plant hormone, which plays an important role in the regulation of plant growth and development, including seed longevity, seed germination, anti-aging, hypocotyl elongation, leaf development, reproductive organ development and abiotic stress. However, the role of 14-3-3 gene of Z. japonica in GA signaling pathway is still unclear. Methods and results Here, we found that the gibberellin content of Arabidopsis overexpressing ZjGRF1, 14-3-3 gene of Z. japonica, is lower than that of wild type (WT), and the expression of gibberellin synthesis genes is lower than that of WT. The expression level of gibberellin receptors in transgenic ZjGRF1 Arabidopsis was lower than that in WT. The expression level of GA response genes EXP8 in transgenic ZjGRF1 Arabidopsis was lower than that in WT, and the expression levels of PRE1, PRE5 and SCL3 were higher than that in WT. Transgenic ZjGRF1 Arabidopsis is insensitive to paclobutrazol, an inhibitor of gibberellin synthesis. The expression level of flowering regulatory genes in transgenic ZjGRF1 Arabidopsis was lower than that in WT. Conclusion This is the first report on the function of 14-3-3 gene family in seagrass. Our findings can be further utilized in future studies on regulation of 14-3-3 gene on plant development.

Genome-wide Identification and Expression Analysis of the GRAS Transcription Factor Family and its Response to Abiotic Stress in Sorghum [Sorghum bicolor (L.) Moench]

Background: GRAS is a very important family of transcription factors that are unique to plants, playing important roles in plant development and their response to abiotic stress. Since the sequencing of the sorghum genome, a large number of genetic studies based on this genomic information have been carried out. Nevertheless, no detailed identification or genome-wide analysis of GRAS family genes in Sorghum bicolor has been published.Results: A total of 81 SbGRAS genes were identified based on the S. bicolor genome. They were named SbGRAS01 to SbGRAS81 and grouped into 13 subfamilies (LISCL, DLT, OS19, SCL4/7, PAT1, SHR, SCL3, HAM-1, SCR, DELLA, HAM-2, LAS and OS4). SbGRAS genes are not evenly distributed on the chromosomes, and we found tandem duplication events and segmental duplications of SbGRAS genes on S. bicolor chromosomes. According to the results of the gene and motif composition, SbGRAS members located in the same group contained analogous intron/exon and motif organizations. By quantitative (q) RT-PCR, we quantified the expression of SbGRAS members in different plant tissues and in plants exposed to six abiotic stresses at the seedling stage. We also measured gibberellin content under the different abiotic stresses.Conclusions: We identified 81 SbGRAS genes and further analyzed their structural composition, and evolution and expression patterns of SbGRAS proteins. The latter analysis indicated that SbGRAS is important in the course of plant development and its response to abiotic stress. Collectively, this systematic analysis lays the foundation for further study of the functional characteristics of GRAS genes of S. bicolor.

FIS1 encodes a GA2-oxidase that regulates fruit firmness in tomato

Fruit firmness is a target trait in tomato breeding because it facilitates transportation and storage. However, it is also a complex trait and uncovering the molecular genetic mechanisms controlling fruit firmness has proven challenging. Here, we report the map-based cloning and functional characterization of qFIRM SKIN 1 (qFIS1), a major quantitative trait locus that partially determines the difference in compression resistance between cultivated and wild tomato accessions. FIS1 encodes a GA2-oxidase, and its mutation leads to increased bioactive gibberellin content, enhanced cutin and wax biosynthesis, and increased fruit firmness and shelf life. Importantly, FIS1 has no unfavorable effect on fruit weight or taste, making it an ideal target for breeders. Our study demonstrates that FIS1 mediates gibberellin catabolism and regulates fruit firmness, and it offers a potential strategy for tomato breeders to produce firmer fruit.

Mutation of Arabidopsis Copper-Containing Amine Oxidase Gene AtCuAOδ Alters Polyamines, Reduces Gibberellin Content and Affects Development

Polyamines (PAs) are essential metabolites in plants performing multiple functions during growth and development. Copper-containing amine oxidases (CuAOs) catalyse the catabolism of PAs and in Arabidopsis thaliana are encoded by a gene family. Two mutants of one gene family member, AtCuAOδ, showed delayed seed germination, leaf emergence, and flowering time. The height of the primary inflorescence shoot was reduced, and developmental leaf senescence was delayed. Siliques were significantly longer in mutant lines and contained more seeds. The phenotype of AtCuAOδ over-expressors was less affected. Before flowering, there was a significant increase in putrescine in AtCuAOδ mutant leaves compared to wild type (WT), while after flowering both spermidine and spermine concentrations were significantly higher than in WT leaves. The expression of GA (gibberellic acid) biosynthetic genes was repressed and the content of GA1, GA7, GA8, GA9, and GA20 was reduced in the mutants. The inhibitor of copper-containing amine oxidases, aminoguanidine hydrochloride, mimicked the effect of AtCuAOδ mutation on WT seed germination. Delayed germination, reduced shoot height, and delayed flowering in the mutants were rescued by GA3 treatment. These data strongly suggest AtCuAOδ is an important gene regulating PA homeostasis, and that a perturbation of PAs affects plant development through a reduction in GA biosynthesis.

Hormonal Regulation of Early Fruit Development in European Pear (Pyrus communis cv. ‘Conference’)

European pear requires inter-cultivar cross-pollination by insects to develop fertilized fruits. However, some European pear cultivars such as ‘Conference’ naturally produce parthenocarpic seedless fruits. To better understand the hormonal regulation of fruit set and early fruit development in this European pear cultivar, the phytohormone and polyamine profiles in ‘Conference’ flowers and fruits resulting from both fertilization and parthenocarpic processes were analyzed. The expression of genes involved in phytohormone metabolism and signaling were also investigated. Phytohormone profiles differed more at flower stage 3 days after treatment than in 15 day- and 30-day-old fruits in response to fertilization and parthenocarpy. An increase in auxins, abscisic acid, ethylene precursor, and spermine, and a decrease in putrescine were recorded in the fertilized flowers as compared to the parthenocarpic flowers. Fertilization also upregulated genes involved in gibberellin synthesis and down-regulated genes involved in gibberellin catabolism although the total gibberellin content was not modified. Moreover, exogenous gibberellin (GA3, GA4/7) and cytokinin (6BA) applications did not increase parthenocarpic induction in ‘Conference’ as observed in other European and Asian pear cultivars. We hypothesize that the intrinsic parthenocarpy of ‘Conference’ could be related to a high gibberellin level in the flowers explaining why exogenous gibberellin application did not increase parthenocarpy as observed in other pear cultivars and species.