Rice early flowering1, a CKI, phosphorylates DELLA protein SLR1 to negatively regulate gibberellin signalling

C-TERMINAL DOMAIN PHOSPHATASE-LIKE 3 contributes to GA-mediated growth and flowering by interaction with DELLA proteins

Gibberellic acid (GA) plays a central role in many plant developmental processes and is crucial for crop improvement. DELLA proteins, the core suppressors in the GA signaling pathway, are degraded by GA via the 26S proteasomal pathway to release the GA response. However, little is known about the phosphorylation-mediated regulation of DELLA proteins. In this study, we combined GA response assays with protein-protein interaction analysis to infer the connection between Arabidopsis thaliana DELLAs and the C-TERMINAL DOMAIN PHOSPHATASE-LIKE 3 (CPL3), a phosphatase involved in the dephosphorylation of RNA polymerase II. We show that CPL3 directly interacts with DELLA proteins and promotes DELLA protein stability by inhibiting its degradation by the 26S proteasome. Consequently, CPL3 negatively modulates multiple GA-mediated processes of plant development, including hypocotyl elongation, flowering time, and anthocyanin accumulation. Taken together, our findings demonstrate that CPL3 serves as a novel regulator that could improve DELLA stability and thereby participate in GA signaling transduction.

A major gene for chilling tolerance variation in Indica rice codes for a kinase OsCTK1 that phosphorylates multiple substrates under cold

Rice is susceptible to chilling stress. Identifying chilling tolerance genes and their mechanisms are key to improve rice performance. Here, we performed a genome-wide association study to identify regulatory genes for chilling tolerance in rice. One major gene for chilling tolerance variation in Indica rice was identified as a casein kinase gene OsCTK1. Its function and natural variation are investigated at the physiological and molecular level by its mutants and transgenic plants. Potential substrates of OsCTK1 were identified by phosphoproteomic analysis, protein-protein interaction assay, in vitro kinase assay, and mutant characterization. OsCTK1 positively regulates rice chilling tolerance. Three of its putative substrates, acidic ribosomal protein OsP3B, cyclic nucleotide-gated ion channel OsCNGC9, and dual-specific mitogen-activated protein kinase phosphatase OsMKP1, are each involved in chilling tolerance. In addition, a natural OsCTK1 chilling-tolerant (CT) variant exhibited a higher kinase activity and conferred greater chilling tolerance compared with a chilling-sensitive (CS) variant. The CT variant is more prevalent in CT accessions and is distributed more frequently in higher latitude compared with the CS variant. This study thus enables a better understanding of chilling tolerance mechanisms and provides gene variants for genetic improvement of chilling tolerance in rice.

Genome-wide evolutionary analysis of TKL_CTR1-DRK-2 gene family and functional characterization reveals that TaCTR1 positively regulates flowering time in wheat

BACKGROUND

Flowering time has an important effect on regional adaptation and yields for crops. The tyrosine kinase-like (TKL) gene family is widely existed and participates in many biological processes in plants. Furthermore, only few TKLs have been characterized functions in controlling flowering time in wheat.

RESULTS

Here, we report that TaCTR1, a tyrosine kinase-like (TKL) gene, regulates flowering time in wheat. Based on identification and evolutionary analysis of TKL_CTR1-DRK-2 subfamily in 15 plants, we proposed an evolutionary model for TaCTR1, suggesting that occurrence of some exon fusion events during evolution. The overexpression of TaCTR1 caused early flowering time in transgenic lines. Transcriptomics analysis enabled identification of mass differential expression genes including plant hormone (ET, ABA, IAA, BR) signaling, flavonoid biosynthesis, phenolamides and antioxidant, and flowering-related genes in TaCTR1 overexpression transgenic lines compared with WT plants. qRT-PCR results showed that the expression levels of ethylene (ET) signal-related genes (ETR, EIN, ERF) and flowering-related genes (FT, PPD1, CO, PRR, PHY) were altered in TaCTR1-overexpressing wheat compared with WT plants. Metabonomics analysis showed that flavonoid contents were altered.

CONCLUSIONS

Thus, the results show that TaCTR1 plays a positive role in controlling flowering time by activating various signaling pathways and regulating flowering-related genes, and will provide new insights on the mechanisms of wheat flowering regulation.

Overexpression of Calcineurin B-like Interacting Protein Kinase 31 Promotes Lodging and Sheath Blight Resistance in Rice

A breakthrough "Green Revolution" in rice enhanced lodging resistance by using gibberellin-deficient semi-dwarf varieties. However, the gibberellic acid (GA) signaling regulation on rice disease resistance remains unclear. The resistance test showed that a positive GA signaling regulator DWARF1 mutant d1 was more susceptible while a negative GA signaling regulator Slender rice 1 (SLR1) mutant was less susceptible to sheath blight (ShB), one of the major rice diseases, suggesting that GA signaling positively regulates ShB resistance. To isolate the regulator, which simultaneously regulates rice lodging and ShB resistance, SLR1 interactors were isolated. Yeast two-hybrid (Y2H), bimolecular fluorescence complementation (BiFC), and Co-IP assay results indicate that SLR1 interacts with Calcineurin B-like-interacting protein kinase 31 (CIPK31). cipk31 mutants exhibited normal plant height, but CIPK31 OXs showed semi-dwarfism. In addition, the SLR1 level was much higher in CIPK31 OXs than in the wild-type, suggesting that CIPK31 OX might accumulate SLR1 to inhibit GA signaling and thus regulate its semi-dwarfism. Recently, we demonstrated that CIPK31 interacts and inhibits Catalase C (CatC) to accumulate ROS, which promotes rice disease resistance. Interestingly, CIPK31 interacts with Vascular Plant One Zinc Finger 2 (VOZ2) in the nucleus, and expression of CIPK31 accumulated VOZ2. Inoculation of Rhizoctonia solani AG1-IA revealed that the voz2 mutant was more susceptible to ShB. Thus, these data prove that CIPK31 promotes lodging and ShB resistance by regulating GA signaling and VOZ2 in rice. This study provides a valuable reference for rice ShB-resistant breeding.

Highlights in gibberellin research: A tale of the dwarf and the slender

It has been almost a century since biologically active gibberellin (GA) was isolated. Here, we give a historical overview of the early efforts in establishing the GA biosynthesis and catabolism pathway, characterizing the enzymes for GA metabolism, and elucidating their corresponding genes. We then highlight more recent studies that have identified the GA receptors and early GA signaling components (DELLA repressors and F-box activators), determined the molecular mechanism of DELLA-mediated transcription reprograming, and revealed how DELLAs integrate multiple signaling pathways to regulate plant vegetative and reproductive development in response to internal and external cues. Finally, we discuss the GA transporters and their roles in GA-mediated plant development.

OsOFP6 Overexpression Alters Plant Architecture, Grain Shape, and Seed Fertility

OVATE family proteins (OFPs) play important roles in plant growth and development, hormone signaling, and stress response pathways. However, the functions of OsOFPs in rice are largely unknown. In this study, a novel gain-of-function rice mutant, Osofp6-D, was identified. This mutant exhibited decreased plant height, erect leaves, reduced panicle size, short and wide seeds, delayed seed germination time, and reduced fertility. These phenotypic changes were attributed to the increased expression of OsOFP6, which was caused by a T-DNA insertion. Complementation of the Osofp6-D phenotype by knockout of OsOFP6 using the CRISPR/Cas9 system confirmed that the Osofp6-D phenotype was caused by OsOFP6 overexpression. In addition, transgenic plants overexpressing OsOFP6 with the 35S promoter mimicked the Osofp6-D phenotype. Cytological observations of the glumes showed that OsOFP6 overexpression altered the grain shape, mainly by altering the cell shape. Hormone response experiments showed that OsOFP6 was involved in the gibberellin (GA) and brassinolide (BR) signaling responses. Further studies revealed that OsOFP6 interacts with E3BB, which is orthologous to the Arabidopsis central organ size-control protein BIG BROTHER (BB). This study further elucidates the regulation mechanism of the rice OFP family on plant architecture and grain shape.

OsCSN2 orchestrates Oryza sativa L. growth and development through modulation of the GA and BR pathways

The COP9 signalosome (CSN) is a conserved protein complex found in higher eukaryotes, consisting of eight subunits, and it plays a crucial role in regulating various processes of plant growth and development. Among these subunits, CSN2 is one of the most conserved components within the COP9 signalosome complex. Despite its prior identification in other species, its specific function in Oryza sativa L. (Rice) has remained poorly understood. In this study, we investigated the role of CSN2 in rice using gene editing CRISPR/Cas9 technology and overexpression techniques. We created two types of mutants: the oscsn2 mutant and the OsCSN2-OE mutant, both in the background of rice, and also generated point mutants of OsCSN2 (OsCSN2K64E, OsCSN2K67E, OsCSN2K71E and OsCSN2K104E) to further explore the regulatory function of OsCSN2. Phenotypic observation and gene expression analysis were conducted on plants from the generated mutants, tracking their growth from the seedling to the heading stages. The results showed that the loss and modification of OsCSN2 had limited effects on plant growth and development during the early stages of both the wild-type and mutant plants. However, as the plants grew to 60 days, significant differences emerged. The OsCSN2 point mutants exhibited increased tillering compared to the OsCSN2-OE mutant plants, which were already at the tillering stage. On the other hand, the OsCSN2 point mutant had already progressed to the heading and flowering stages, with the shorter plants. These results, along with functional predictions of the OsCSN2 protein, indicated that changes in the 64th, 67th, 71st, and 104th amino acids of OsCSN2 affected its ubiquitination site, influencing the ubiquitination function of CSN and consequently impacting the degradation of the DELLA protein SLR1. Taken together, it can be speculated that OsCSN2 plays a key role in GA and BR pathways by influencing the functional regulation of the transcription factor SLR1 in CSN, thereby affecting the growth and development of rice and the number of tillers.

Advance Research on the Pre-Harvest Sprouting Trait in Vegetable Crop Seeds

Pre-harvest sprouting (PHS), the germination of seeds on the plant prior to harvest, poses significant challenges to agriculture. It not only reduces seed and grain yield, but also impairs the commodity quality of the fruit, ultimately affecting the success of the subsequent crop cycle. A deeper understanding of PHS is essential for guiding future breeding strategies, mitigating its impact on seed production rates and the commercial quality of fruits. PHS is a complex phenomenon influenced by genetic, physiological, and environmental factors. Many of these factors exert their influence on PHS through the intricate regulation of plant hormones responsible for seed germination. While numerous genes related to PHS have been identified in food crops, the study of PHS in vegetable crops is still in its early stages. This review delves into the regulatory elements, functional genes, and recent research developments related to PHS in vegetable crops. Meanwhile, this paper presents a novel understanding of PHS, aiming to serve as a reference for the study of this trait in vegetable crops.

Mining novel genomic regions and candidate genes of heading and flowering dates in bread wheat by SNP- and haplotype-based GWAS

Bread wheat (Triticum aestivum L.) is a global staple crop vital for human nutrition. Heading date (HD) and flowering date (FD) are critical traits influencing wheat growth, development, and adaptability to diverse environmental conditions. A comprehensive study were conducted involving 190 bread wheat accessions to unravel the genetic basis of HD and FD using high-throughput genotyping and multi-environment field trials. Seven independent quantitative trait loci (QTLs) were identified to be significantly associated with HD and FD using two GWAS methods, which explained a proportion of phenotypic variance ranging from 1.43% to 9.58%. Notably, QTLs overlapping with known vernalization genes Vrn-D1 were found, validating their roles in regulating flowering time. Moreover, novel QTLs on chromosome 2A, 5B, 5D, and 7B associated with HD and FD were identified. The effects of these QTLs on HD and FD were confirmed in an additional set of 74 accessions across different environments. An increase in the frequency of alleles associated with early flowering in cultivars released in recent years was also observed, suggesting the influence of molecular breeding strategies. In summary, this study enhances the understanding of the genetic regulation of HD and FD in bread wheat, offering valuable insights into crop improvement for enhanced adaptability and productivity under changing climatic conditions. These identified QTLs and associated markers have the potential to improve wheat breeding programs in developing climate-resilient varieties to ensure food security.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01422-z.

Phosphorylation Promotes DELLA Activity by Enhancing Its Binding to Histone H2A at Target Chromatin in Arabidopsis

DELLA proteins are conserved master growth regulators that play a central role in controlling plant development in response to internal and environmental cues. DELLAs function as transcription regulators, which are recruited to target promoters by binding to transcription factors (TFs) and histone H2A via its GRAS domain. Recent studies showed that DELLA stability is regulated post-translationally via two mechanisms, phytohormone gibberellin-induced polyubiquitination for its rapid degradation, and Small Ubiquitin-like Modifier (SUMO)- conjugation to alter its accumulation. Moreover, DELLA activity is dynamically modulated by two distinct glycosylations: DELLA-TF interactions are enhanced by O -fucosylation, but inhibited by O -linked N -acetylglucosamine ( O -GlcNAc) modification. However, the role of DELLA phosphorylation remains unclear. Here, we identified phosphorylation sites in REPRESSOR OF ga1-3 (RGA, an AtDELLA) purified from Arabidopsis by tandem mass spectrometry analysis, and showed that phosphorylation of the RGA LKS-peptide in the poly- S/T region enhances RGA-H2A interaction and RGA association with target promoters. Interestingly, phosphorylation does not affect RGA-TF interactions. Our study has uncovered that phosphorylation is a new regulatory mechanism of DELLA activity.

Data-independent acquisition-based global phosphoproteomics reveal the diverse roles of casein kinase 1 in plant development

Casein kinase 1 (CK1) is serine/threonine protein kinase highly conserved among eukaryotes, and regulates multiple developmental and signaling events through phosphorylation of target proteins. Arabidopsis early flowering 1 (EL1)-like (AELs) are plant-specific CK1s with varied functions, but identification and validation of their substrates is a major bottleneck in elucidating their physiological roles. Here, we conducted a quantitative phosphoproteomic analysis in data-independent acquisition mode to systematically identify CK1 substrates. We extracted proteins from seedlings overexpressing individual AEL genes (AEL1/2/3/4-OE) or lacking AEL function (all ael single mutants and two triple mutants) to identify the high-confidence phosphopeptides with significantly altered abundance compared to wild-type Col-0. Among these, we selected 3985 phosphopeptides with higher abundance in AEL-OE lines or lower abundance in ael mutants compared with Col-0 as AEL-upregulated phosphopeptides, and defined 1032 phosphoproteins. Eight CK1s substrate motifs were enriched among AEL-upregulated phosphopeptides and verified, which allowed us to predict additional candidate substrates and functions of CK1s. We functionally characterized a newly identified substrate C3H17, a CCCH-type zinc finger transcription factor, through biochemical and genetic analyses, revealing a role for AEL-promoted C3H17 protein stability and transactivation activity in regulating embryogenesis. As CK1s are highly conserved across eukaryotes, we searched the rice, mouse, and human protein databases using newly identified CK1 substrate motifs, yielding many more candidate substrates than currently known, largely expanding our understanding of the common and distinct functions exerted by CK1s in Arabidopsis and humans, facilitating future mechanistic studies of CK1-mediated phosphorylation in different species.

Environmental control of rice flowering time

Correct measurement of environmental parameters is fundamental for plant fitness and survival, as well as for timing developmental transitions, including the switch from vegetative to reproductive growth. Important parameters that affect flowering time include day length (photoperiod) and temperature. Their response pathways have been best described in Arabidopsis, which currently offers a detailed conceptual framework and serves as a comparison for other species. Rice, the focus of this review, also possesses a photoperiodic flowering pathway, but 150 million years of divergent evolution in very different environments have diversified its molecular architecture. The ambient temperature perception pathway is strongly intertwined with the photoperiod pathway and essentially converges on the same genes to modify flowering time. When observing network topologies, it is evident that the rice flowering network is centered on EARLY HEADING DATE 1, a rice-specific transcriptional regulator. Here, we summarize the most important features of the rice photoperiodic flowering network, with an emphasis on its uniqueness, and discuss its connections with hormonal, temperature perception, and stress pathways.

GSK3 phosphorylates and regulates the Green Revolution protein Rht-B1b to reduce plant height in wheat

The utilization of stabilized DELLA proteins Rht-B1b and Rht-D1b was crucial for increasing wheat (Triticum aestivum) productivity during the Green Revolution. However, the underlying mechanisms remain to be clarified. Here, we cloned a gain-of-function allele of the GSK3/SHAGGY-like kinase-encoding gene GSK3 by characterizing a dwarf wheat mutant. Furthermore, we determined that GSK3 interacts with and phosphorylates the Green Revolution protein Rht-B1b to promote it to reduce plant height in wheat. Specifically, phosphorylation by GSK3 may enhance the activity and stability of Rht-B1b, allowing it to inhibit the activities of its target transcription factors. Taken together, we reveal a positive regulatory mechanism for the Green Revolution protein Rht-B1b by GSK3, which might have contributed to the Green Revolution in wheat.

The E3 ubiquitin ligases SINA1 and SINA2 integrate with the protein kinase CIPK20 to regulate the stability of RGL2a, a positive regulator of anthocyanin biosynthesis

Although DELLA protein destabilization mediated by post-translational modifications is essential for gibberellin (GA) signal transduction and GA-regulated anthocyanin biosynthesis, the related mechanisms remain largely unknown. In this study, we report the ubiquitination and phosphorylation of an apple DELLA protein MdRGL2a in response to GA signaling and its regulatory role in anthocyanin biosynthesis. MdRGL2a could interact with MdWRKY75 to enhance the MdWRKY75-activated transcription of anthocyanin activator MdMYB1 and interfere with the interaction between anthocyanin repressor MdMYB308 and MdbHLH3 or MdbHLH33, thereby promoting anthocyanin accumulation. A protein kinase MdCIPK20 was found to phosphorylate and protect MdRGL2a from degradation, and it was essential for MdRGL2a-promoting anthocyanin accumulation. However, MdRGL2a and MdCIPK20 were ubiquitinated and degraded by E3 ubiquitin ligases MdSINA1 and MdSINA2, respectively, both of which were activated in the presence of GA. Our results display the integration of SINA1/2 with CIPK20 to dynamically regulate GA signaling and will be helpful toward understanding the mechanism of GA signal transduction and GA-inhibited anthocyanin biosynthesis. The discovery of extensive interactions between DELLA and SINA and CIPK proteins in apple will provide reference for the study of ubiquitination and phosphorylation of DELLA proteins in other species.

Combined genome-wide association study and epistasis analysis reveal multifaceted genetic architectures of plant height in Asian cultivated rice

Plant height (PH) in rice (Oryza sativa) is an important trait for its adaptation and agricultural performance. Discovery of the semi-dwarf1 (SD1) mutation initiated the Green Revolution, boosting rice yield and fitness, but the underlying genetic regulation of PH in rice remains largely unknown. Here, we performed genome-wide association study (GWAS) and identified 12 non-repetitive QTL/genes regulating PH variation in 619 Asian cultivated rice accessions. One of these was an SD1 structural variant, not normally detected in standard GWAS analyses. Given the strong effect of SD1 on PH, we also divided 619 accessions into subgroups harbouring distinct SD1 haplotypes, and found a further 85 QTL/genes for PH, revealing genetic heterogeneity that may be missed by analysing a broad, diverse population. Moreover, we uncovered two epistatic interaction networks of PH-associated QTL/genes in the japonica (Geng)-dominant SD1^NIP subgroup. In one of them, the hub QTL/gene qphSN1.4/GAMYB interacted with qphSN3.1/OsINO80, qphSN3.4/HD16/EL1, qphSN6.2/LOC_Os06g11130, and qphSN10.2/MADS56. Sequence variations in GAMYB and MADS56 were associated with their expression levels and PH variations, and MADS56 was shown to physically interact with MADS57 to coregulate expression of gibberellin (GA) metabolic genes OsGA2ox3 and Elongated Uppermost Internode1 (EUI1). Our study uncovered the multifaceted genetic architectures of rice PH, and provided novel and abundant genetic resources for breeding semi-dwarf rice and new candidates for further mechanistic studies on regulation of PH in rice.

Integrating Transcriptomics and Hormones Dynamics Reveal Seed Germination and Emergence Process in Polygonatum cyrtonema Hua

Polygonatum cyrtonema Hua is a traditional Chinese herb propagated using rhizomes, and excessive demand for seedlings and quality deterioration caused by rhizome propagation has highlighted that seed propagation may be an ideal solution to address these issues. However, the molecular mechanisms involved in P. cyrtonema Hua seed germination and emergence stages are not well understood. Therefore, in the present study, we performed transcriptomics combined with hormone dynamics during different seed germination stages, and 54,178 unigenes with an average length of 1390.38 bp (N50 = 1847 bp) were generated. Significant transcriptomic changes were related to plant hormone signal transduction and the starch and carbohydrate pathways. Genes related to ABA(abscisic acid), IAA(Indole acetic acid), and JA(Jasmonic acid) signaling, were downregulated, whereas genes related to ethylene, BR(brassinolide), CTK(Cytokinin), and SA(salicylic acid) biosynthesis and signaling were activated during the germination process. Interestingly, GA biosynthesis- and signaling-related genes were induced during the germination stage but decreased in the emergence stage. In addition, seed germination significantly upregulated the expression of genes associated with starch and sucrose metabolism. Notably, raffinose biosynthesis-related genes were induced, especially during the emergence stage. In total, 1171 transcription factor (TF) genes were found to be differentially expressed. Our results provide new insights into the mechanisms underlying P. cyrtonema Hua seed germination and emergence processes and further research for molecular breeding.

Uncovering the involvement of DoDELLA1-interacting proteins in development by characterizing the DoDELLA gene family in Dendrobium officinale

BACKGROUND

Gibberellins (GAs) are widely involved in plant growth and development. DELLA proteins are key regulators of plant development and a negative regulatory factor of GA. Dendrobium officinale is a valuable traditional Chinese medicine, but little is known about D. officinale DELLA proteins. Assessing the function of D. officinale DELLA proteins would provide an understanding of their roles in this orchid's development.

RESULTS

In this study, the D. officinale DELLA gene family was identified. The function of DoDELLA1 was analyzed in detail. qRT-PCR analysis showed that the expression levels of all DoDELLA genes were significantly up-regulated in multiple shoots and GA3-treated leaves. DoDELLA1 and DoDELLA3 were significantly up-regulated in response to salt stress but were significantly down-regulated under drought stress. DoDELLA1 was localized in the nucleus. A strong interaction was observed between DoDELLA1 and DoMYB39 or DoMYB308, but a weak interaction with DoWAT1.

CONCLUSIONS

In D. officinale, a developmental regulatory network involves a close link between DELLA and other key proteins in this orchid's life cycle. DELLA plays a crucial role in D. officinale development.

Genomic footprints of selection in early-and late-flowering pearl millet landraces

Pearl millet is among the top three-cereal production in one of the most climate vulnerable regions, sub-Saharan Africa. Its Sahelian origin makes it adapted to grow in poor sandy soils under low soil water regimes. Pearl millet is thus considered today as one of the most interesting crops to face the global warming. Flowering time, a trait highly correlated with latitude, is one of the key traits that could be modulated to face future global changes. West African pearl millet landraces, can be grouped into early- (EF) and late-flowering (LF) varieties, each flowering group playing a specific role in the functioning and resilience of Sahelian smallholders. The aim of this study was thus to detect genes linked to flowering but also linked to relevant traits within each flowering group. We thus investigated genomic and phenotypic diversity in 109 pearl millet landrace accessions, i.e., 66 early-flowering and 43 late-flowering, grown in the groundnut basin, the first area of rainfed agriculture in Senegal dominated by dry cereals (millet, maize, and sorghum) and legumes (groundnuts, cowpeas). We were able to confirm the role of PhyC gene in pearl millet flowering and identify several other genes that appear to be as much as important, such as FSR12 and HAC1. HAC1 and two other genes appear to be part of QTLs previously identified and deserve further investigation. At the same time, we were able to highlight a several genes and variants that could contribute to the improvement of pearl millet yield, especially since their impact was demonstrated across flowering cycles.

The genetic basis for panicle trait variation in switchgrass (Panicum virgatum)

We investigate the genetic basis of panicle architecture in switchgrass in two mapping populations across a latitudinal gradient, and find many stable, repeatable genetic effects and limited genetic interactions with the environment. Grass species exhibit large diversity in panicle architecture influenced by genes, the environment, and their interaction. The genetic study of panicle architecture in perennial grasses is limited. In this study, we evaluate the genetic basis of panicle architecture including panicle length, primary branching number, and secondary branching number in an outcrossed switchgrass QTL population grown across ten field sites in the central USA through multi-environment mixed QTL analysis. We also evaluate genetic effects in a diversity panel of switchgrass grown at three of the ten field sites using genome-wide association (GWAS) and multivariate adaptive shrinkage. Furthermore, we search for candidate genes underlying panicle traits in both of these independent mapping populations. Overall, 18 QTL were detected in the QTL mapping population for the three panicle traits, and 146 unlinked genomic regions in the diversity panel affected one or more panicle trait. Twelve of the QTL exhibited consistent effects (i.e., no QTL by environment interactions or no QTL × E), and most (four of six) of the effects with QTL × E exhibited site-specific effects. Most (59.3%) significant partially linked diversity panel SNPs had significant effects in all panicle traits and all field sites and showed pervasive pleiotropy and limited environment interactions. Panicle QTL co-localized with significant SNPs found using GWAS, providing additional power to distinguish between true and false associations in the diversity panel.

Phosphorylation of plant virus proteins: Analysis methods and biological functions

Phosphorylation is one of the most extensively investigated post-translational modifications that orchestrate a variety of cellular signal transduction processes. The phosphorylation of virus-encoded proteins plays an important regulatory role in the infection cycle of such viruses in plants. In recent years, molecular mechanisms underlying the phosphorylation of plant viral proteins have been widely studied. Based on recent publications, our study summarizes the phosphorylation analyses of plant viral proteins and categorizes their effects on biological functions according to the viral life cycle. This review provides a theoretical basis for elucidating the molecular mechanisms of viral infection. Furthermore, it deepens our understanding of the biological functions of phosphorylation in the interactions between plants and viruses.

Dynamics of Protein Phosphorylation during Arabidopsis Seed Germination

Seed germination is critical for early plantlet development and is tightly controlled by environmental factors. Nevertheless, the signaling networks underlying germination control remain elusive. In this study, the remodeling of Arabidopsis seed phosphoproteome during imbibition was investigated using stable isotope dimethyl labeling and nanoLC-MS/MS analysis. Freshly harvested seeds were imbibed under dark or constant light to restrict or promote germination, respectively. For each light regime, phosphoproteins were extracted and identified from dry and imbibed (6 h, 16 h, and 24 h) seeds. A large repertoire of 10,244 phosphopeptides from 2546 phosphoproteins, including 110 protein kinases and key regulators of seed germination such as Delay Of Germination 1 (DOG1), was established. Most phosphoproteins were only identified in dry seeds. Early imbibition led to a similar massive downregulation in dormant and non-dormant seeds. After 24 h, 411 phosphoproteins were specifically identified in non-dormant seeds. Gene ontology analyses revealed their involvement in RNA and protein metabolism, transport, and signaling. In addition, 489 phosphopeptides were quantified, and 234 exhibited up or downregulation during imbibition. Interaction networks and motif analyses revealed their association with potential signaling modules involved in germination control. Our study provides evidence of a major role of phosphosignaling in the regulation of Arabidopsis seed germination.

Genomic and GWAS analyses demonstrate phylogenomic relationships of Gossypium barbadense in China and selection for fibre length, lint percentage and Fusarium wilt resistance

Sea Island cotton (Gossypium barbadense) is the source of the world's finest fibre quality cotton, yet relatively little is understood about genetic variations among diverse germplasms, genes underlying important traits and the effects of pedigree selection. Here, we resequenced 336 G. barbadense accessions and identified 16 million SNPs. Phylogenetic and population structure analyses revealed two major gene pools and a third admixed subgroup derived from geographical dissemination and interbreeding. We conducted a genome-wide association study (GWAS) of 15 traits including fibre quality, yield, disease resistance, maturity and plant architecture. The highest number of associated loci was for fibre quality, followed by disease resistance and yield. Using gene expression analyses and VIGS transgenic experiments, we confirmed the roles of five candidate genes regulating four key traits, that is disease resistance, fibre length, fibre strength and lint percentage. Geographical and temporal considerations demonstrated selection for the superior fibre quality (fibre length and fibre strength), and high lint percentage in improving G. barbadense in China. Pedigree selection breeding increased Fusarium wilt disease resistance and separately improved fibre quality and yield. Our work provides a foundation for understanding genomic variation and selective breeding of Sea Island cotton.

Integration of transcriptomic and proteomic analyses reveals several levels of metabolic regulation in the excess starch and early senescent leaf mutant lses1 in rice

BACKGROUND

The normal metabolism of transitory starch in leaves plays an important role in ensuring photosynthesis, delaying senescence and maintaining high yield in crops. OsCKI1 (casein kinase I1) plays crucial regulatory roles in multiple important physiological processes, including root development, hormonal signaling and low temperature-treatment adaptive growth in rice; however, its potential role in regulating temporary starch metabolism or premature leaf senescence remains unclear. To reveal the molecular regulatory mechanism of OsCKI1 in rice leaves, physiological, transcriptomic and proteomic analyses of leaves of osckI1 allele mutant lses1 (leaf starch excess and senescence 1) and its wild-type varieties (WT) were performed.

RESULTS

Phenotypic identification and physiological measurements showed that the lses1 mutant exhibited starch excess in the leaves and an obvious leaf tip withering phenotype as well as high ROS and MDA contents, low chlorophyll content and protective enzyme activities compared to WT. The correlation analyses between protein and mRNA abundance are weak or limited. However, the changes of several important genes related to carbohydrate metabolism and apoptosis at the mRNA and protein levels were consistent. The protein-protein interaction (PPI) network might play accessory roles in promoting premature senescence of lses1 leaves. Comprehensive transcriptomic and proteomic analysis indicated that multiple key genes/proteins related to starch and sugar metabolism, apoptosis and ABA signaling exhibited significant differential expression. Abnormal increase in temporary starch was highly correlated with the expression of starch biosynthesis-related genes, which might be the main factor that causes premature leaf senescence and changes in multiple metabolic levels in leaves of lses1. In addition, four proteins associated with ABA accumulation and signaling, and three CKI potential target proteins related to starch biosynthesis were up-regulated in the lses1 mutant, suggesting that LSES1 may affect temporary starch accumulation and premature leaf senescence through phosphorylation crosstalk ABA signaling and starch anabolic pathways.

CONCLUSION

The current study established the high correlation between the changes in physiological characteristics and mRNA and protein expression profiles in lses1 leaves, and emphasized the positive effect of excessive starch on accelerating premature leaf senescence. The expression patterns of genes/proteins related to starch biosynthesis and ABA signaling were analyzed via transcriptomes and proteomes, which provided a novel direction and research basis for the subsequent exploration of the regulation mechanism of temporary starch and apoptosis via LSES1/OsCKI1 in rice.

Interactions of Gibberellins with Phytohormones and Their Role in Stress Responses

Gibberellins are amongst the main plant growth regulators. Discovered over a century ago, the interest in gibberellins research is growing due to their current and potential applications in crop production and their role in the responses to environmental stresses. In the present review, the current knowledge on gibberellins’ homeostasis and modes of action is outlined. Besides this, the complex interrelations between gibberellins and other plant growth regulators are also described, providing an intricate network of interactions that ultimately drives towards precise and specific gene expression. Thus, genes and proteins identified as being involved in gibberellin responses in model and non-model species are highlighted. Furthermore, the molecular mechanisms governing the gibberellins’ relation to stress responses are also depicted. This review aims to provide a comprehensive picture of the state-of-the-art of the current perceptions of the interactions of gibberellins with other phytohormones, and their responses to plant stresses, thus allowing for the identification of the specific mechanisms involved. This knowledge will help us to improve our understanding of gibberellins’ biology, and might help increase the biotechnological toolbox needed to refine plant resilience, particularly under a climate change scenario.

Nitric oxide negatively regulates gibberellin signaling to coordinate growth and salt tolerance in Arabidopsis

In response to dynamically altered environments, plants must finely coordinate the balance between growth and stress responses for their survival. However, the underpinning regulatory mechanisms remain largely elusive. The phytohormone gibberellin promotes growth via a derepression mechanism by proteasomal degradation of the DELLA transcription repressors. Conversely, the stress-induced burst of nitric oxide (NO) enhances stress tolerance, largely relaying on NO-mediated S-nitrosylation, a redox-based posttranslational modification. Here, we show that S-nitrosylation of Cys-374 in the Arabidopsis RGA protein, a key member of DELLAs, inhibits its interaction with the F-box protein SLY1, thereby preventing its proteasomal degradation under salinity condition. The accumulation of RGA consequently retards growth but enhances salt tolerance. We propose that NO negatively regulates gibberellin signaling via S-nitrosylation of RGA to coordinate the balance of growth and stress responses when challenged by adverse environments.

Transcriptome and Metabolite Conjoint Analysis Reveals the Seed Dormancy Release Process in Callery Pear

Seed dormancy transition is a vital developmental process for seedling propagation and agricultural production. The process is precisely regulated by diverse endogenous genetic factors and environmental cues. Callery pear (Pyrus calleryana Decne) is an important rootstock species that requires cold stratification to break seed dormancy, but the mechanisms underlying pear seed dormancy release are not yet fully understood. Here, we analyzed the transcriptome profiles at three different stages of cold stratification in callery pear seeds using RNA sequencing combined with phytohormone and sugar content measurements. Significant alterations in hormone contents and carbohydrate metabolism were observed and reflected the dormancy status of the seeds. The expressions of genes related to plant hormone metabolism and signaling transduction, including indole-3-acetic acid (IAA) biosynthesis (ASAs, TSA, NITs, YUC, and AAO) genes as well as several abscisic acid (ABA) and gibberellic acid (GA) catabolism and signaling transduction genes (CYP707As, GA2ox, and DELLAs), were consistent with endogenous hormone changes. We further found that several genes involved in cytokinin (CTK), ethylene (ETH), brassionolide (BR), and jasmonic acid (JA) metabolism and signaling transduction were differentially expressed and integrated in pear seed dormancy release. In accordance with changes in starch and soluble sugar contents, the genes associated with starch and sucrose metabolism were significantly up-regulated during seed dormancy release progression. Furthermore, the expression levels of genes involved in lipid metabolism pathways were also up-regulated. Finally, 447 transcription factor (TF) genes (including ERF, bHLH, bZIP, NAC, WRKY, and MYB genes) were observed to be differentially expressed during seed cold stratification and might relate to pear seed dormancy release. Our results suggest that the mechanism underlying pear seed dormancy release is a complex, transcriptionally regulated process involving hormones, sugars, lipids, and TFs.

RID1 sets rice heading date by balancing its binding with SLR1 and SDG722

Rice (Oryza sativa) is a major crop that feeds billions of people, and its yield is strongly influenced by flowering time (heading date). Loss of RICE INDETERMINATE1 (RID1) function causes plants not to flower; thus, RID1 is considered a master switch among flowering-related genes. However, it remains unclear whether other proteins function together with RID1 to regulate rice floral transition. Here, we revealed that the chromatin accessibility and H3K9ac, H3K4me3, and H3K36me3 levels at Heading date 3a (Hd3a) and RICE FLOWERING LOCUS T1 (RFT1) loci were significantly reduced in rid1 mutants. Notably, RID1 interacted with SET DOMAIN GROUP PROTEIN 722 (SDG722), a methyltransferase. We determined that SDG722 affects the global level of H3K4me2/3 and H3K36me2/3, and promotes flowering primarily through the Early heading date1-Hd3a/RFT1 pathway. We further established that rice DELLA protein SLENDER RICE1 (SLR1) interacted with RID1 to inhibit its transactivation activity, that SLR1 suppresses rice flowering, and that messenger RNA and protein levels of SLR1 gradually decrease with plant growth. Furthermore, SLR1 competed with SDG722 for interaction with RID1. Overall, our results establish that interplay between RID1, SLR1, and SDG722 feeds into rice flowering-time control.

The converging path of protein SUMOylation in phytohormone signalling: highlights and new frontiers

The intersection of phytohormone signalling pathways with SUMOylation, a key post-translational modification, offers an additional layer of control to the phytohormone signalling for sophisticated regulation of plant development. Plants live in a constantly changing environment that are often challenging for the growth and development of plants. Phytohormones play a critical role in modulating molecular-level changes for enabling plants to resist climatic aberrations. The orchestration of such effective molecular responses entails rapid regulation of phytohormone signalling at transcriptional, translational and post-translational levels. Post-translational modifications have emerged as a key player in modulating hormonal pathways. The current review lays emphasis on the role of SUMOylation, a key post-translational modification, in manipulating individual hormone signalling pathways for better plant adaptability. Here, we discuss the recent advancement in the field and highlights how SUMO targets key signalling intermediates including transcription factors to provide a quick response to different biotic or abiotic stresses, sometimes even prior to changes in hormone levels. The understanding of the convergence of SUMOylation and hormonal pathways will offer an additional layer of control to the phytohormone signalling for an intricate and sophisticated regulation of plant development and can be utilised as a tool to generate climate-resilient crops.

Plant casein kinases phosphorylate and destabilize a cyclin-dependent kinase inhibitor to promote cell division

Cell cycle is one of the most fundamentally conserved biological processes of plants and mammals. Casein kinase1s (CK1s) are critical for cell proliferation in mammalian cells; however, how CK1s coordinate cell division in plants remains unknown. Through genetic and biochemical studies, here we demonstrated that plant CK1, Arabidopsis (Arabidopsis thaliana) EL1-like (AELs), regulate cell cycle/division by modulating the stability and inhibitory effects of Kip-related protein6 (KRP6) through phosphorylation. Cytological analysis showed that AELs deficiency results in suppressed cell-cycle progression mainly due to the decreased DNA replication rate at S phase and increased period of G2 phase. AELs interact with and phosphorylate KRP6 at serines 75 and 109 to stimulate KRP6's interaction with E3 ligases, thus facilitating the KRP6 degradation through the proteasome. These results demonstrate the crucial roles of CK1s/AELs in regulating cell division through modulating cell-cycle rates and elucidate how CK1s/AELs regulate cell division by destabilizing the stability of cyclin-dependent kinase inhibitor KRP6 through phosphorylation, providing insights into the plant cell-cycle regulation through CK1s-mediated posttranslational modification.

Whole-genome resequencing of 240 Gossypium barbadense accessions reveals genetic variation and genes associated with fiber strength and lint percentage

KEY MESSAGE

Genetic variation in a G. barbadense population was revealed using resquencing. GWAS on G.barbadense population identified several candidate genes associated with fiber strength and lint percentage. Gossypium barbadense is the second-largest cultivated cotton species planted in the world, which is characterized by high fiber quality. Here, we described the global pattern of genetic polymorphisms for 240 G. barbadense accessions based on the whole-genome resequencing. A total of 3,632,231 qualified single-nucleotide polymorphisms (SNPs) and 221,354 insertion-deletions (indels) were obtained. We conducted a genome-wide association study (GWAS) on 12 traits under four environments. Two traits with more stable associated variants, fiber strength and lint percentage, were chosen for further analysis. Three putative candidate genes, HD16 orthology (GB_D11G3437), WDL2 orthology (GB_D11G3460) and TUBA1 orthology (GB_D11G3471), on chromosome D11 were found to be associated with fiber strength, and one gene orthologous to Arabidopsis Receptor-like protein kinase HERK 1 (GB_A07G1034) was predicated to be the candidate gene for the lint percentage improvement. The identified genes may serve as promising targets for genetic engineering to accelerate the breeding process for G. barbadense and the high-density genome variation map constructed in this work may facilitate our understanding of the genetic architecture of cotton traits.

Genomic signatures of natural selection at phenology-related genes in a widely distributed tree species Fagus sylvatica L

BACKGROUND

Diversity among phenology-related genes is predicted to be a contributing factor in local adaptations seen in widely distributed plant species that grow in climatically variable geographic areas, such as forest trees. European beech (Fagus sylvatica L.) is widespread, and is one of the most important broadleaved tree species in Europe; however, its potential for adaptation to climate change is a matter of uncertainty, and little is known about the molecular basis of climate change-relevant traits like bud burst.

RESULTS

We explored single nucleotide polymorphisms (SNP) at candidate genes related to bud burst in beech individuals sampled across 47 populations from Europe. SNP diversity was monitored for 380 candidate genes using a sequence capture approach, providing 2909 unlinked SNP loci. We used two complementary analytical methods to find loci significantly associated with geographic variables, climatic variables (expressed as principal components), or phenotypic variables (spring and autumn phenology, height, survival). Redundancy analysis (RDA) was used to detect candidate markers across two spatial scales (entire study area and within subregions). We revealed 201 candidate SNPs at the broadest scale, 53.2% of which were associated with phenotypic variables. Additive polygenic scores, which provide a measure of the cumulative signal across significant candidate SNPs, were correlated with a climate variable (first principal component, PC1) related to temperature and precipitation availability, and spring phenology. However, different genotype-environment associations were identified within Southeastern Europe as compared to the entire geographic range of European beech.

CONCLUSIONS

Environmental conditions play important roles as drivers of genetic diversity of phenology-related genes that could influence local adaptation in European beech. Selection in beech favors genotypes with earlier bud burst under warmer and wetter habitats within its range; however, selection pressures may differ across spatial scales.

Understanding and Exploiting Post-Translational Modifications for Plant Disease Resistance

Plants are constantly threatened by pathogens, so have evolved complex defence signalling networks to overcome pathogen attacks. Post-translational modifications (PTMs) are fundamental to plant immunity, allowing rapid and dynamic responses at the appropriate time. PTM regulation is essential; pathogen effectors often disrupt PTMs in an attempt to evade immune responses. Here, we cover the mechanisms of disease resistance to pathogens, and how growth is balanced with defence, with a focus on the essential roles of PTMs. Alteration of defence-related PTMs has the potential to fine-tune molecular interactions to produce disease-resistant crops, without trade-offs in growth and fitness.

Phosphorylation-mediated signalling in flowering: prospects and retrospects of phosphoproteomics in crops

Protein phosphorylation is a major post-translational modification, regulating protein function, stability, and subcellular localization. To date, annotated phosphorylation data are available mainly for model organisms and humans, despite the economic importance of crop species and their large kinomes. Our understanding of the phospho-regulation of flowering in relation to the biology and interaction between the pollen and pistil is still significantly lagging, limiting our knowledge on kinase signalling and its potential applications to crop production. To address this gap, we bring together relevant literature that were previously disconnected to present an overview of the roles of phosphoproteomic signalling pathways in modulating molecular and cellular regulation within specific tissues at different morphological stages of flowering. This review is intended to stimulate research, with the potential to increase crop productivity by providing a platform for novel molecular tools.

Interaction of BTB-TAZ protein MdBT2 and DELLA protein MdRGL3a regulates nitrate-mediated plant growth

Nitrate acts as a vital signal molecule in the modulation of plant growth and development. The phytohormones gibberellin (GA) is also involved in this process. However, the exact molecular mechanism of how nitrate and GA signaling pathway work together in regulating plant growth remains poorly understood. In this study, we found that a nitrate-responsive BTB/TAZ protein MdBT2 participates in regulating nitrate-induced plant growth in apple (Malus × domestica). Yeast two-hybridization, protein pull-down, and bimolecular fluorescence complementation (BiFC) assays showed that MdBT2 interacts with a DELLA protein MdRGL3a, which is required for the ubiquitination and degradation of MdRGL3a proteins via a 26S proteasome-dependent pathway. Furthermore, heterologous expression of MdBT2 partially rescued growth inhibition caused by overexpression of MdRGL3a in Arabidopsis. Taken together, our findings indicate that MdBT2 promotes nitrate-induced plant growth partially through reducing the abundance of the DELLA protein MdRGL3a.

Transcriptional and post-transcriptional regulation of heading date in rice

Rice is a facultative short day (SD) plant. In addition to serving as a model plant for molecular genetic studies of monocots, rice is a staple crop for about half of the world's population. Heading date is a critical agronomic trait, and many genes controlling heading date have been cloned over the last 2 decades. The mechanism of flowering in rice from recognition of day length by leaves to floral activation in the shoot apical meristem has been extensively studied. In this review, we summarise current progress on transcriptional and post-transcriptional regulation of heading date in rice, with emphasis on post-translational modifications of key regulators, including Heading date 1 (Hd1), Early heading date 1 (Ehd1), Grain number, plant height, and heading date7 (Ghd7). The contribution of heading date genes to heterosis and the expansion of rice cultivation areas from low-latitude to high-latitude regions are also discussed. To overcome the limitations of diverse genetic backgrounds used in heading date studies and to gain a clearer understanding of flowering in rice, we propose a systematic collection of genetic resources in a common genetic background. Strategies in breeding adapted cultivars by rational design are also discussed.

Quantitative Proteomics and Phosphoproteomics Support a Role for Mut9-Like Kinases in Multiple Metabolic and Signaling Pathways in Arabidopsis

Protein phosphorylation is one of the most prevalent posttranslational modifications found in eukaryotic systems. It serves as a key molecular mechanism that regulates protein function in response to environmental stimuli. The Mut9-like kinases (MLKs) are a plant-specific family of Ser/Thr kinases linked to light, circadian, and abiotic stress signaling. Here we use quantitative phosphoproteomics in conjunction with global proteomic analysis to explore the role of the MLKs in daily protein dynamics. Proteins involved in light, circadian, and hormone signaling, as well as several chromatin-modifying enzymes and DNA damage response factors, were found to have altered phosphorylation profiles in the absence of MLK family kinases. In addition to altered phosphorylation levels, mlk mutant seedlings have an increase in glucosinolate metabolism enzymes. Subsequently, we show that a functional consequence of the changes to the proteome and phosphoproteome in mlk mutant plants is elevated glucosinolate accumulation and increased sensitivity to DNA damaging agents. Combined with previous reports, this work supports the involvement of MLKs in a diverse set of stress responses and developmental processes, suggesting that the MLKs serve as key regulators linking environmental inputs to developmental outputs.

•

MUT9-LIKE KINASE mutant quantitative proteome and phosphoproteome measured.

•

Changes to proteome and phosphoproteome are specific to genotype and environment.

•

Loss of MLKs alters glucosinolate enzyme abundance and metabolism.

•

Loss of MLKs increases plant sensitivity to UV radiation and DNA damage agents.

Overexpression of ovate family protein 22 confers multiple morphological changes and represses gibberellin and brassinosteroid signalings in transgenic rice

OVATE family proteins (OFPs) are plant-specific transcription factors that regulate plant growth and development. OFPs interact with 3-aa loop extension (TALE) homeodomain proteins and brassinosteroid (BR) signaling components to modulate gibberellic acid (GA) biosynthesis and BR responses. Bioactive GAs are essential in regulating plant organogenesis and organ growth by promoting cell differentiation and elongation. DELLA proteins act as the central repressors of GA-regulated processes and are targeted to be degraded by the 26S proteasome in the presence of GA. We discovered that the rice OFP22 negatively regulates GA and BR signal transduction. OsOFP22 expression was rapidly up-regulated by exogenous GA and BR application, detected predominantly in the calli and spikelets. Overexpression of OsOFP22 conferred multiple morphological phenotypes, including reduced plant height, dark green leaves, and shortened and widened leaves, floral organs and grains. The GA-induced elongation of the second leaf sheath in the seedlings, and α-amylase activity in the endosperms were attenuated in transgenic lines overexpressing OsOFP22, while GA-biosynthesis gene transcripts and bioactive GA₃ and GA₄ contents were increased in the transgenic plants. OsOFP22 promotes the protein accumulation of SLR1, the single DELLA in rice protein. Furthermore, Overexpression of OsOFP22 suppresses BR response and the expression of BR-related genes. OsOFP22 is thus involved in the repression of GA and BR signal transduction and integrates GA with BR to regulate plant growth and development.

MLK4-mediated phosphorylation of histone H3T3 promotes flowering by transcriptional silencing of FLC/MAF in Arabidopsis thaliana

Casein kinase I (CK1), a ubiquitous Ser/Thr protein kinase in eukaryotes, plays a critical role in higher plant flowering. Arabidopsis CK1 family member MUT9-LIKE KINASEs, such as MLK1 and MLK3, have been shown to phosphorylate histone H3 at threonine 3 (H3T3), an evolutionarily conserved residue, and the modification is associated with the transcriptional repression of euchromatic and heterochromatic loci. This study demonstrates that mlk4-3, a T-DNA insertion mutant of MLK4, flowered late, and that overexpression of MLK4 caused early flowering. The nuclear protein MLK4 phosphorylated histone H3T3 both in vitro and in vivo, and this catalytic activity required the conserved lysine residue K175. mutation of MLK4 at K175 failed to restore the level of phosphorylated H3T3 (H3T3ph) or to complement the phenotypic defects of mlk4-3. The FLC/MAF-clade genes, including FLC, MAF4 and MAF5, were significantly upregulated in mlk4-3. The double mutant mlk4-3 flc-3 flowered earlier than mlk4-3, suggesting that functional FLC is crucial for flowering repression in mlk4-3. Chromatin immunoprecipitation assays showed that MLK4 bound to FLC/MAF chromatin and that H3T3ph occupancy at the promoter of FLC/MAF was negatively associated with its transcriptional level. In accordance, H3T3ph accumulated at FLC/MAF in 35S::MLK4/mlk4-3 but diminished in 35S::MLK4(K175R)/mlk4-3 plants. Moreover, the amount of RNA Pol II deposited at FLC/MAF was clearly enriched in mlk4-3 relative to the wild type. Therefore, MLK4-dependent phosphorylation of H3T3 contributes to accelerating flowering by repressing the transcription of negative flowering regulator FLC/MAF. This study sheds light on the delicate control of flowering by the plant-specific CK1, MLK4, via post-translational modification of histone H3.

Interactions between ScNAC23 and ScGAI regulate GA-mediated flowering and senescence in sugarcane

Control of gene transcription is crucial to regulate plant growth and development events, such as flowering, leaf senescence, and seed germination. Here we identified a NAC transcription factor (ScNAC23) isolated from sugarcane (cv. ROC22). Analysis by qRT-PCR indicated that ScNAC23 expression was strongly induced in mature leaves and flowering varieties and was also responsive to exogenous treatment with the hormone gibberellin (GA). Ectopic expression of ScNAC23 in Arabidopsis accelerated bolting, flowering, and leaf senescence compared to wild type plants. Furthermore, Arabidopsis overexpressed ScNAC23 were more sensitive to GA than the wild type, and exogenous GA significantly accelerated flowering and senescence in the ScNAC23-overexpressed ones. A direct interaction between ScNAC23 and ScGAI, an inhibitor of GA signaling, was confirmed by yeast-two hybrid, bimolecular fluorescence complementation, and GST-pull down assay. The putative GA-ScNAC23-LFY/SAGs regulator module might provide a new sight into the molecular action of GA to accelerating flowering and leaf senescence in sugarcane.

Genetic Elucidation for Response of Flowering Time to Ambient Temperatures in Asian Rice Cultivars

Climate resilience of crops is critical for global food security. Understanding the genetic basis of plant responses to ambient environmental changes is key to developing resilient crops. To detect genetic factors that set flowering time according to seasonal temperature conditions, we evaluated differences of flowering time over years by using chromosome segment substitution lines (CSSLs) derived from japonica rice cultivars "Koshihikari" × "Khao Nam Jen", each with different robustness of flowering time to environmental fluctuations. The difference of flowering times in 9 years' field tests was large in "Khao Nam Jen" (36.7 days) but small in "Koshihikari" (9.9 days). Part of this difference was explained by two QTLs. A CSSL with a "Khao Nam Jen" segment on chromosome 11 showed 28.0 days' difference; this QTL would encode a novel flowering-time gene. Another CSSL with a segment from "Khao Nam Jen" in the region around Hd16 on chromosome 3 showed 23.4 days" difference. A near-isogenic line (NIL) for Hd16 showed 21.6 days' difference, suggesting Hd16 as a candidate for this QTL. RNA-seq analysis showed differential expression of several flowering-time genes between early and late flowering seasons. Low-temperature treatment at panicle initiation stage significantly delayed flowering in the CSSL and NIL compared with "Koshihikari". Our results unravel the molecular control of flowering time under ambient temperature fluctuations.

The Rice Abscisic Acid-Responsive RING Finger E3 Ligase OsRF1 Targets OsPP2C09 for Degradation and Confers Drought and Salinity Tolerance in Rice

Drought and salinity are major important factors that restrain growth and productivity of rice. In plants, many really interesting new gene (RING) finger proteins have been reported to enhance drought and salt tolerance. However, their mode of action and interacting substrates are largely unknown. Here, we identified a new small RING-H2 type E3 ligase OsRF1, which is involved in the ABA and stress responses of rice. OsRF1 transcripts were highly induced by ABA, salt, or drought treatment. Upregulation of OsRF1 in transgenic rice conferred drought and salt tolerance and increased endogenous ABA levels. Consistent with this, faster transcriptional activation of key ABA biosynthetic genes, ZEP, NCED3, and ABA4, was observed in OsRF1-OE plants compared with wild type in response to drought stress. Yeast two-hybrid assay, BiFC, and co-immunoprecipitation analysis identified clade A PP2C proteins as direct interacting partners with OsRF1. In vitro ubiquitination assay indicated that OsRF1 exhibited E3 ligase activity, and that it targeted OsPP2C09 protein for ubiquitination and degradation. Cell-free degradation assay further showed that the OsPP2C09 protein is more rapidly degraded by ABA in the OsRF1-OE rice than in the wild type. The combined results suggested that OsRF1 is a positive player of stress responses by modulating protein stability of clade A PP2C proteins, negative regulators of ABA signaling.

Protein Phosphorylation Response to Abiotic Stress in Plants

Plants are an important part of nature because as photoautotrophs, they provide a nutrient source for many other living organisms. Due to their sessile nature, to overcome both biotic and abiotic stresses, plants have developed intricate mechanisms for perception of and reaction to these stresses, both on an external level (perception) and on an internal level (reaction). Specific proteins found within cells play crucial roles in stress mitigation by enhancing cellular processes that facilitate the plants survival during the unfavorable conditions. Well before plants are able to synthesize nascent proteins in response to stress, proteins which already exist in the cell can be subjected to an array of posttranslation modifications (PTMs) that permit a rapid response. These activated proteins can, in turn, aid in further stress responses. Different PTMs have different functions in growth and development of plants. Protein phosphorylation, a reversible form of modification has been well elucidated, and its role in signaling cascades is well documented. In this mini-review, we discuss the integration of protein phosphorylation with other components of abiotic stress-responsive pathways including phytohormones and ion homeostasis. Overall, this review demonstrates the high interconnectivity of the stress response system in plants and how readily plants are able to toggle between various signaling pathways in order to survive harsh conditions. Most notably, fluctuations of the cytosolic calcium levels seem to be a linking component of the various signaling pathways.

Regulation of DELLA Proteins by Post-translational Modifications

DELLA proteins are the negative regulators of the gibberellin (GA) signaling pathway. GAs have a pervasive effect on plant physiology, influencing processes that span the entire life cycle of the plant. All the information encoded by GAs, either environmental or developmental in origin, is canalized through DELLAs, which modulate the activity of many transcription factors and transcriptional regulators. GAs unlock the signaling pathway by triggering DELLA polyubiquitination and degradation by the 26S proteasome. Recent reports indicate, however, that there are other pathways that trigger DELLA polyubiquitination and degradation independently of GAs. Moreover, results gathered during recent years indicate that other post-translational modifications (PTMs), namely phosphorylation, SUMOylation and glycosylation, modulate DELLA function. The convergence of several PTMs in DELLA therefore highlights the strict regulation to which these proteins are subject. In this review, we summarize these discoveries and discuss DELLA PTMs from an evolutionary perspective and examine the possibilities these and other post-translational regulations offer to improve DELLA-dependent agronomic traits.

Origin and evolution of gibberellin signaling and metabolism in plants

Gibberellins modulate multiple aspects of plant behavior. The molecular mechanism by which these hormones are perceived and how this information is translated into transcriptional changes has been elucidated in vascular plants: gibberellins are perceived by the nuclear receptor GID1, which then interacts with the DELLA nuclear proteins and promote their degradation, resulting in the modification of the activity of transcription factors with which DELLAs interact physically. However, several important questions are still pending: how does a single molecule perform such a vast array of functions along plant development? What property do gibberellins add to plant behavior? A closer look at gibberellin action from an evolutionary perspective can help answer these questions. DELLA proteins are conserved in all land plants, and predate the emergence of a full gibberellin metabolic pathway and the GID1 receptor in the ancestor of vascular plants. The origin of gibberellin signaling is linked to the exaptation by GID1 of the N-terminal domain in DELLA, which already acted as a transcriptional coactivator domain in the ancestral DELLA proteins. At least the ability to control plant growth seems to be encoded already in the ancestral DELLA protein too, suggesting that gibberellins' functional diversity is the direct consequence of DELLA protein activity. Finally, comparative network analysis suggests that gibberellin signaling increases the coordination of transcriptional responses, providing a theoretical framework for the role of gibberellins in plant adaptation at the evolutionary scale, which further needs experimental testing.

Plant hormonal changes and differential expression profiling reveal seed dormancy removal process in double dormant plant-herbaceous peony

Herbaceous peony (Paeonia lactiflora Pall.) is a popular ornamental and medicinal plant. Taking approximately six to seven months, the seeds germination under natural conditions experiences dual dormancies, which seriously affects horticultural cultivation. Few studies have been conducted on exploring both biological and molecular mechanism that regulates dormancy removal process in hypocotyls double dormant plants. Here, we first measured ABA and GA₃ content changes at four key dormancy break stages, and then performed transcriptomic analyses to identify the differentially expressed genes (DEGs) using RNA-seq. We subsequently carried out Quantitative real-time PCR (qRT-PCR) to validate RNA-seq data. ABA content decreased during the whole dormancy removal process and GA₃ content exhibited decreasing slightly and then increasing trend. RNA sequencing de novo assembly generated a total of 99,577 unigenes. 20,344 unigenes were differentially expressed in the whole dormancy release process. The qPCR results of 54 selected unigenes were consistent with the FPKM values obtained from RNA-seq. Our results summarize a valuable collection of gene expression profiles characterizing the dormancy release process. The DEGs are candidates for functional analyses of genes affecting the dormancy release, which is a precious resource for the on-going physiological and molecular investigation of seeds dormancy removal in other perennial plants.

Arabidopsis thaliana MLK3, a Plant-specific Casein Kinase 1, Negatively Regulates Flowering and Phosphorylates Histone H3 in Vitro

Arabidopsis thalianaMUT9-LIKE KINASES (MLKs), a family of the plant-specific casein kinase 1 (CK1), have been implicated collectively in multiple biological processes including flowering. Three of the four MLKs (MLK1/2/4) have been characterized, however, little is known about MLK3, the most divergent member of MLKs. Here, we demonstrated that disruption of MLK3 transcript in mlk3 caused early flowering with retarded leaf growth under long-day conditions. In vitro kinase assay showed the nuclear protein MLK3 phosphorylated histone 3 at threonine 3 (H3T3) and mutation of a conserved residue (K146R) abolished the catalytic activity. Ectopic expression of MLK3 but not MLK3(K146R) rescued the morphological defects of mlk3, indicating that an intact MLK3 is critical for maintaining proper flowering time. Transcriptomic analysis revealed that the floral repressor FLOWERING LOCUS C (FLC) was down-regulated significantly in mlk3, suggesting that MLK3 negatively regulates flowering. Hence, MLK3 plays a role in repressing the transition from vegetative to reproductive phase in A. thaliana. This study sheds light on the delicate control of flowering time by A. thaliana CK1 specific to the plant kingdom.

Mut9p-LIKE KINASE Family Members: New Roles of the Plant-Specific Casein Kinase I in Plant Growth and Development

: Casein kinase I (CK1), a ubiquitous serine/threonine (Ser/Thr) protein kinase in eukaryotes, plays pivotal roles in a wide spectrum of cellular functions including metabolism, cell cycle progression, developmental control and stress responses. Plant CK1 evolves a lineage expansion, resulting in a unique branch of members exclusive to the kingdom. Among them, Arabidopsis Mut9p-LIKE KINASEs (MLKs) target diverse substrates including histones and the key regulatory proteins involving in physiological processes of light signaling, circadian rhythms, phytohormone and plant defense. Deregulation of the kinase activity by mutating the enzyme or the phosphorylation sites of substrates causes developmental disorders and susceptibility to adverse environmental conditions. MLKs have evolved as a general kinase that modifies transcription factors or primary regulatory proteins in a dynamic way. Here, we summarize the current knowledge of the roles of MLKs and MLK orthologs in several commercially important crops.

Mutations on ent-kaurene oxidase 1 encoding gene attenuate its enzyme activity of catalyzing the reaction from ent-kaurene to ent-kaurenoic acid and lead to delayed germination in rice

Rice seed germination is a critical step that determines its entire life circle, with seeds failing to germinate or pre-harvest sprouting both reduce grain yield. Nevertheless, the mechanisms underlying this complex biological event remain unclear. Previously, gibberellin has been shown to promote seed germination. In this study, a delayed seed germination rice mutant was obtained through screening of the EMS induced mutants. Besides of delayed germination, it also shows semi-dwarfism phenotype, which could be recovered by exogenous GA. Through re-sequencing on the mutant, wild-type and their F2 populations, we identified two continuous mutated sites on ent-kaurene oxidase 1 (OsKO1) gene, which result in the conversion from Thr to Met in the cytochrome P450 domain. Genetic complementary analysis and enzyme assay verified that the mutations in OsKO1 gene block the biosynthesis of GA and result in the defect phenotypes. Further analyses proved that OsKO1 could catalyze the reaction from ent-kaurene into ent-kaurenoic acid in GA biosynthesis mainly at seed germination and seedling stages, and the mutations decrease its activity to catalyze the step from ent-kaurenol to ent-kaurenoic acid in this reaction. Transcriptomic and proteomic data indicate that the defect on GA biosynthesis decreases its ability to mobilize starch and attenuate ABA signaling, therefore delay the germination process. The results provide some new insights into both GA biosynthesis and seed germination regulatory pathway in rice.