Dt1 inhibits SWEET-mediated sucrose transport to regulate photoperiod-dependent seed weight in soybean.

Soybean is a photoperiod-sensitive short-day crop whose reproductive period and yield are markedly affected by day-length changes. Seed weight is one of the key traits determining the soybean yield; however, the prominent genes that control the final seed weight of soybean and the mechanisms underlying the photoperiod's effect on this trait remain poorly understood. In this study, we identify SW19 as a major locus controlling soybean seed weight by QTL mapping and determine Dt1, an orthologous gene of Arabidopsis TFL1 that is known to govern the soybean growth habit, as the causal gene of the SW19 locus. We showed that Dt1 is highly expressed in developing seeds and regulates photoperiod-dependent seed weight in soybean. Further analyses revealed that the Dt1 protein physically interacts with the sucrose transporter GmSWEET10a to negatively regulate the import of sucrose from seed coat to the embryo, thus modulating seed weight under long days. However, Dt1 does not function in seed development under short days due to its very low expression. Importantly, we discovered a novel natural allelic variant of Dt1 (H4 haplotype) that decouples its pleiotropic effects on seed size and growth habit; i.e., this variant remains functional in seed development but fails to regulate the stem growth habit of soybean. Collectively, our findings provide new insights into how soybean seed development responds to photoperiod at different latitudes, offering an ideal genetic component for improving soybean's yield by manipulating its seed weight and growth habit.

Gibberellin signaling modulates flowering via the DELLA-BRAHMA-NF-YC module in Arabidopsis.

Gibberellin (GA) plays a key role in floral induction by activating the expression of floral integrator genes in plants, but the epigenetic regulatory mechanisms underlying this process remain unclear. Here, we show that BRAHMA (BRM), a core subunit of the chromatin-remodeling SWItch/sucrose nonfermentable (SWI/SNF) complex that functions in various biological processes by regulating gene expression, is involved in GA-signaling-mediated flowering via the formation of the DELLA-BRM-NF-YC module in Arabidopsis (Arabidopsis thaliana). DELLA, BRM, and NF-YC transcription factors interact with one another, and DELLA proteins promote the physical interaction between BRM and NF-YC proteins. This impairs the binding of NF-YCs to SOC1, a major floral integrator gene, to inhibit flowering. On the other hand, DELLA proteins also facilitate the binding of BRM to SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1). The GA-induced degradation of DELLA proteins disturbs the DELLA-BRM-NF-YC module, prevents BRM from inhibiting NF-YCs, and decreases the DNA-binding ability of BRM, which promote the deposition of H3K4me3 on SOC1 chromatin, leading to early flowering. Collectively, our findings show that BRM is a key epigenetic partner of DELLA proteins during the floral transition. Moreover, they provide molecular insights into how GA signaling coordinates an epigenetic factor with a transcription factor to regulate the expression of a flowering gene and flowering in plants.

Transcriptome Analysis Reveals Clues into leaf-like flower mutant in Chinese orchid Cymbidium ensifolium.

The floral morphology of Cymbidium ensifolium, a well-known orchid in China, has increasingly attracted horticultural and commercial attention. However, the molecular mechanisms that regulate flower development defects in C. ensifolium mutants are poorly understood. In this work, we examined a domesticated variety of C. ensifolium named 'CuiYuMuDan', or leaf-like flower mutant, which lacks typical characteristics of orchid floral organs but continues to produce sepal-to leaf-like structures along the inflorescence. We used comparative transcriptome analysis to identify 6234 genes that are differentially expressed between mutant and wild-type flowers. The majority of these differentially expressed genes are involved in membrane-building, anabolism regulation, and plant hormone signal transduction, implying that in the leaf-like mutant these processes play roles in the development of flower defects. In addition, we identified 152 differentially expressed transcription factors, including the bHLH, MYB, MIKC, and WRKY gene families. Moreover, we found 20 differentially expressed genes that are commonly involved in flower development, including MADS-box genes, CLAVATA3 (CLV3), WUSCHEL (WUS), and PERIANTHIA (PAN). Among them, floral homeotic genes were further investigated by phylogenetic analysis and expression validation, which displayed distinctive spatial expression patterns and significant changes between the wild type and the mutant. This is the first report on the C. ensifolium leaf-like flower mutant transcriptome. Our results shed light on the molecular regulation of orchid flower development, and may improve our understanding of floral patterning regulation and advance molecular breeding of Chinese orchids.

bHLH104 confers tolerance to cadmium stress in Arabidopsis thaliana.

Cd is a non-essential heavy metal that is toxic to both plants and animals. Here, we reveal that the transcription factor bHLH104 positively regulates Cd tolerance in Arabidopsis thaliana. We show that Fe deficiency-responsive genes were induced by Cd treatment, and that their upregulation was suppressed in bhlh104 loss-of-function mutants, but enhanced upon overexpression of bHLH104. Correspondingly, the bhlh104 mutants displayed sensitivity to Cd stress, whereas plants overexpressing bHLH104 exhibited enhanced Cd tolerance. Further analysis suggested that bHLH104 positively regulates four heavy metal detoxification-associated genes, IREG2, MTP3, HMA3 and NAS4, which play roles in Cd sequestration and tolerance. The bHLH104 overexpression plants accumulated high levels of Cd in the root but low levels of Cd in the shoot, which might contribute to the Cd tolerance in those lines. The present study thus points to bHLH104 as a potentially useful tool for genetic engineering of plants with enhanced Cd tolerance.

POSITIVE REGULATOR OF IRON HOMEOSTASIS1, OsPRI1, Facilitates Iron Homeostasis.

Oryza sativa HEMERYTHRIN MOTIF-CONTAINING REALLY INTERESTING NEW GENE AND ZINC-FINGER PROTEIN1 (OsHRZ1) is a putative iron-binding sensor. However, it is unclear how OsHRZ1 transmits signals. In this study, we reveal that POSITIVE REGULATOR OF IRON HOMEOSTASIS1 (OsPRI1) interacts with OsHRZ1. A loss-of-function mutation to OsPRI1 increased the sensitivity of plants to Fe-deficient conditions and down-regulated the expression of Fe-deficiency-responsive genes. Yeast one-hybrid and electrophoretic mobility shift assay results suggested that OsPRI1 binds to the OsIRO2 and OsIRO3 promoters. In vitro ubiquitination experiments indicated that OsPRI1 is ubiquitinated by OsHRZ1. Cell-free degradation assays revealed that the stability of OsPRI1 decreased in wild-type roots but increased in the hrz1-2 mutant, suggesting OsHRZ1 is responsible for the instability of OsPRI1. The hrz1-2 seedlings were insensitive to Fe-deficient conditions. When the pri1-1 mutation was introduced into hrz1-2 mutants, the pri1hrz1 double mutant was more sensitive to Fe deficiency than the hrz1-2 mutant. Additionally, the expression levels of Fe-deficiency-responsive genes were lower in the hrz1pri1 double mutant than in the hrz1-2 mutant. Collectively, these results imply that OsPRI1, which is ubiquitinated by OsHRZ1, mediates rice responses to Fe deficiency by positively regulating OsIRO2 and OsIRO3 expression as part of the OsHRZ1-OsPRI1-OsIRO2/3 signal transduction cascade.

Fe-deficiency-induced expression of bHLH104 enhances Fe-deficiency tolerance of Arabidopsis thaliana.

MAIN CONCLUSION: Expression of bHLH104 - GFP driven by the MYB72 promoter improves plants' tolerance to Fe deficiency and increases seed Fe concentrations. Iron (Fe) deficiency causes reduced crop yield and quality. In humans, Fe deficiency is directly associated with Fe-deficiency anemia. Therefore, breeding Fe-deficiency tolerant and Fe-enriched plants are an ideal approach to deal with these problems. Here, different strategies were explored to generate Fe-deficiency tolerant and Fe-enriched plants. Unexpectedly, the overexpression of Fe-deficiency responsive genes (IRT1, MYB72, and bHLH100) resulted in enhanced sensitivity to Fe deficiency, including leaf chlorosis and short roots under Fe-deficiency conditions. Next, three different types of Fe-deficiency responsive promoters (Pro IRT1 , Pro MYB72, and Pro bHLH100 ) were used to drive the expression of bHLH104-GFP fusion gene in Arabidopsis. Pro IRT1 :bHLH104-GFP plants showed the enhanced sensitivity to Fe deficiency on Fe-deficient media and the reduced fertility in alkaline soil. In contrast, Pro bHLH100 :bHLH104-GFP plants displayed a slight tolerance to Fe deficiency and Pro MYB72 :bHLH104-GFP plants had a significant advantage in growth in alkaline soil, including increased root length, chlorophyll, and biomass. Further analysis revealed that the expression of Fe-deficiency responsive genes was dramatically upregulated in both Pro MYB72 :bHLH104-GFP and Pro bHLH100 :bHLH104-GFP plants under Fe-deficiency conditions. When grown in alkaline soil, Pro MYB72 :bHLH104-GFP plants greatly improved the seed yield and Fe concentration. These results are fundamental for plant manipulation approaches to modify tolerance to Fe deficiency and Fe accumulation through alterations of bHLH104 gene expression.