Mutation of the gene encoding the PHD-type transcription factor SAB23 confers submergence tolerance in rice

Submergence is a major constraint on rice production in South and Southeast Asia. In this study, we determined that a gene of the Sub1A-binding protein family, SAB23, encodes a plant homeodomain (PHD)-type transcription factor that has a novel function of negatively regulating submergence tolerance in rice. The T-DNA insertion mutant sab23 displayed reduced plant height, delayed seed maturation, and lower percentage seed set. Importantly, this mutant also exhibited enhanced submergence tolerance. In addition, CRISPR/Cas9 knock out of SAB23 resulted in a significant reduction in the content of the gibberellin GA4 and a dramatic increase in the content of GA1 in the plants. SAB23 binds to the promoter of CYTOCHROME P450 714B2 (CYP714B2), which encodes a GA13-oxidase that catalyses the conversion of GA53 to GA19. Disruption of SAB23 function led to increased CYP714B2 transcription, and overexpression of CYP714B2 produced phenotypes similar to those of the SAB23-knockout plants. Taken together, our results reveal that SAB23 negatively regulates rice submergence tolerance by modulating CYP714B2 expression, which has significant potential for use in future breeding.

Transcriptomics and targeted metabolomics reveal the regulatory network of Lilium davidii var. unicolor during bulb dormancy release

Through combined analysis of the transcriptome and targeted metabolome of lily bulbs, the possible molecular mechanism of dormancy release was revealed. Regulation of bulb dormancy is critical for ensuring annual production and high-quality cultivation. The application of low temperatures is the most effective method for breaking bulb dormancy, but the molecular mechanism underlying this response is unclear. Herein, targeted metabolome and transcriptome analyses were performed on Lilium davidii var. unicolor bulbs stored for 0, 50, and 100 days at 4 °C. Dormancy release mainly depended on the accumulation of gibberellins GA₄ and GA₇, which are synthesized by the non-13-hydroxylation pathway, rather than GA₃, and ABA was degraded in the process. The contents of nonbioactive GA₉, GA₁₅, and GA₂₄, the precursors of GA₄ synthesis, increased with bulb dormancy release. Altogether, 113,252 unique transcripts were de novo assembled through high-throughput transcriptome sequences, and 639 genes were continuously differentially expressed. Energy sources during carbohydrate metabolism mainly depend on glycolysis and the pentose phosphate pathway. Screening of transcription factor families involved in bulb dormancy release showed that MYB, WRKY, NAC, and TCP members were significantly correlated with the targeted metabolome. Coexpression analysis further confirmed that ABI5, PYL8, PYL4, and PP2C, which are vital ABA signaling elements, regulated GA3ox and GA20ox in the GA₄ biosynthesis pathway, and XERICO may be involved in the regulation of ABA and GA₄ signaling through the ubiquitination pathway. WRKY32, WRKY71, DAM14, NAC8, ICE1, bHLH93, and TCP15 also participated in the ABA/GA₄ regulatory network, and ICE1 may be the key factor linking temperature signals and hormone metabolism. These results will help to reveal the bulb dormancy molecular mechanism and develop new strategies for high-quality bulb production.

Downstream of GA4, PbCYP78A6 participates in regulating cell cycle-related genes and parthenogenesis in pear (Pyrus bretshneideri Rehd.)

BACKGROUND

Parthenocarpy results in traits attractive to both consumers and breeders, and it overcomes the obstacle of self-incompatibility in the fruit set of horticultural crops, including pear (Pyrus bretshneider). However, there is limited knowledge regarding the genetic and molecular mechanisms that regulate parthenogenesis.

RESULTS

Here, in a transcriptional comparison between pollination-dependent fruit and GA₄-induced parthenocarpy, PbCYP78A6 was identified and proposed as a candidate gene involved in parthenocarpy. PbCYP78A6 is similar to Arabidopsis thaliana CYP78A6 and highly expressed in pear hypanthia. The increased PbCYP78A6 expression, as assessed by RT-qPCR, was induced by pollination and GA₄ exposure. The ectopic overexpression of PbCYP78A6 contributed to parthenocarpic fruit production in tomato. The PbCYP78A6 expression coincided with fertilized and parthenocarpic fruitlets development and the expression of fruit development-related genes as assessed by cytological observations and RT-qPCR, respectively. PbCYP78A6 RNA interference and overexpression in pear calli revealed that the gene is an upstream regulator of specific fruit development-related genes in pear.

CONCLUSIONS

Our findings indicate that PbCYP78A6 plays a critical role in fruit formation and provide insights into controlling parthenocarpy.

miR169 and PmRGL2 synergistically regulate the NF-Y complex to activate dormancy release in Japanese apricot (Prunus mume Sieb. et Zucc.)

This study is the first to demonstrate that GA₄-induced dormancy release is associated with the NF-Y complex, which interacts with gibberellin inhibitor RGL2 in Japanese apricot. Seasonal dormancy is not only vital for the survival in cold winter but also affects flowering of temperate fruit trees and the dormancy release depends on the accumulation of the cold temperatures (Chilling requirement-CR). To understand the mechanism of dormancy release in deciduous fruit crops, we compared miRNA sequencing data during the transition stage from paradormancy to dormancy release in the Japanese apricot and found that the miR169 family showed significant differentially up-regulated expression during dormancy induction and was down-regulated during the dormancy release periods. The 5' RACE assay and RT-qPCR validated its target gene NUCLEAR FACTOR-Y subunit A (NF-YA), which exhibited the opposite expression pattern. Further study showed that exogenous GA₄ could inhibit the expression of the gibberellic acid (GA) signal transduction suppressor PmRGL2 (RGA-LIKE 2) and promote the expression of NF-Y. Moreover, the interaction between the NF-Y family and GA inhibitor PmRGL2 was verified by the yeast-two-hybrid (Y2H) system and a bimolecular fluorescence complementarity (BiFC) experiment. These results suggest that synergistic regulation of the NF-Y and PmRGL2 complex leads to the activation of dormancy release induced by GA₄. These findings will help to elucidate the functional and regulatory roles of miR169 and NF-Y complex in seasonal bud dormancy induced by GA in Japanese apricot and provide new insights for the discovery of dormancy release mechanisms in woody plants.

Endodormancy Release Can Be Modulated by the GA4-GID1c-DELLA2 Module in Peach Leaf Buds

Gibberellin (GA) plays a key role in the release of bud dormancy and the GA receptor GID1 (GIBBERELLIN INSENSITIVE DWARF1) and DELLA protein are the GA signaling parts, but the molecular mechanism of GA-GID1-DELLA module regulating leaf bud dormancy in peach (Prunus persica) is still not very clear. In this study, we isolated and characterized the GID1 gene PpGID1c from the peach cultivar "Zhong you No.4." Overexpressing PpGID1c in Arabidopsis promoted seed germination, which indicated that PpGID1c has an important function in dormancy. The expression level of PpGID1c in peach leaf buds during endodormancy release was higher than that during ecodormancy and was positively correlated with GA₄ levels. Our study also found that GA₄ had the most obvious effect on promoting the bud break, indicating that GA₄ may be the key gibberellin to promoting peach leaf bud endodormancy release. Moreover, a quantitative real-time PCR (qRT-PCR) found that GA₄ could increase the expression of the gibberellin signaling gene PpDELLA2. A yeast two-hybrid (Y2H) assay suggested that the PpGID1c interaction with the PpDELLA1 protein was not dependent on gibberellin, while the PpGID1c interaction with PpDELLA2 required GA₄ or another gibberellin. These findings suggested that the GA₄-GID1c-DELLA2 module regulates peach leaf bud endodormancy release, with this finding significantly enhancing our comprehensive understanding of bud endodormancy release and revealing a new mechanism for regulating leaf bud endodormancy release in peach.

Hormone and RNA-seq analyses reveal the mechanisms underlying differences in seed vigour at different maize ear positions

ABA/GA₄ ratio, stress resistance, carbon and nitrogen metabolism, and chromatin structure play important roles in vigour differences of seeds located at different maize ear positions. Seed vigour, which ensures rapid and uniform field emergence across diverse environments, differs at different maize ear positions. However, little is known regarding the associated mechanisms. In this study, we determined that seed vigour, stress resistance, and carbon and nitrogen metabolism were higher in seeds from middle and bottom section of the ear, while the ABA/GA₄ ratio in the embryos was significantly lower. Compared with the seeds subjected to repeated pollination during silking, less variation in seed vigour and the ABA/GA₄ ratio in the embryos was observed in seeds at different ear positions subjected to single pollination after complete silking. This indicated that single pollination can reduce, but not eliminate, the differences in seed vigour at different ear positions. RNA-seq analysis indicated that the seed vigour differences at the different locations of the maize ears of the single pollinated treatment were related to carbon and nitrogen metabolism. In contrast, the differences in seed vigour under repeated pollination were related to chromatin structure. The present study contributes to our understanding of the mechanisms underlying differences in seed vigour at different positions on the maize ear.

Isolation and Role of PmRGL2 in GA-mediated Floral Bud Dormancy Release in Japanese Apricot (Prunus mume Siebold et Zucc.)

Bud dormancy release is regulated by gibberellins (GAs). DELLA proteins are highly conserved and act as negative regulators in GA signaling pathway. The present study established a relationship between PmRGL2 in Japanese apricot and GA₄ levels during dormancy release of floral buds. Overexpression of PmRGL2 in poplar delayed the onset of bud dormancy and resulted in dwarf plants, relative to wild-type trees. PmRGL2 exhibited higher expression during ecodormancy and relatively lower expression during endodormancy. The relative level of GA₄ exhibited an increasing trend at the transition from endodormancy to ecodormancy and displayed a similar expression pattern of genes related to GA metabolism, PmGA20ox2, PmGA3ox1, PmGID1b, in both Japanese apricot and transgenic poplar. These results suggests that PmRGL2 acts as an integrator and negative regulator of dormancy via a GA-signaling pathway. Moreover, an interaction between RGL2 and SLY1 in a yeast two hybrid (Y2H) system further suggests that SCF E3 ubiquitin ligases, such as SLY1, may be a critical factor in the regulation of RGL2 through an SCF ^SLY1 -proteasome pathway. Our study demonstrated that PmRGL2 plays a negative role in bud dormancy release by regulating the GA biosynthetic enzymes, GA20ox and GA3ox1 and the GA receptor, GID1b.

Comparative proteomic and transcriptomic approaches to address the active role of GA4 in Japanese apricot flower bud dormancy release

Hormones are closely associated with dormancy in deciduous fruit trees, and gibberellins (GAs) are known to be particularly important. In this study, we observed that GA4 treatment led to earlier bud break in Japanese apricot. To understand better the promoting effect of GA4 on the dormancy release of Japanese apricot flower buds, proteomic and transcriptomic approaches were used to analyse the mechanisms of dormancy release following GA4 treatment, based on two-dimensional gel electrophoresis (2-DE) and digital gene expression (DGE) profiling, respectively. More than 600 highly reproducible protein spots (P<0.05) were detected and, following GA4 treatment, 38 protein spots showed more than a 2-fold difference in expression, and 32 protein spots were confidently identified according to the databases. Compared with water treatment, many proteins that were associated with energy metabolism and oxidation-reduction showed significant changes after GA4 treatment, which might promote dormancy release. We observed that genes at the mRNA level associated with energy metabolism and oxidation-reduction also played an important role in this process. Analysis of the functions of the identified proteins and genes and the related metabolic pathways would provide a comprehensive proteomic and transcriptomic view of the coordination of dormancy release after GA4 treatment in Japanese apricot flower buds.