Overexpression of the Arabidopsis anaphase promoting complex subunit CDC27a increases growth rate and organ size

The Multifunctional Anaphase Promoting Complex 7 (APC7) Gene Is Associated With Increased Plant Growth and Improved Resistance to DNA and RNA Viruses

The anaphase promoting complex 7 (AtAPC7) is an APC/C subunit expressed in different organs of Arabidopsis thaliana and conserved among eukaryotes. A variant of the complete APC7 protein, containing its C-terminal region (named APC-CT), shows a high homology with a tobacco viral replication inhibitor (IVR-like) protein that reduces plant susceptibility to RNA viruses. Here, the role of the AtAPC7 gene was investigated by characterizing Arabidopsis plants overexpressing the full-length AtAPC7 (APC7OE) and the C-terminal portion (APC7-CTOE), by phenotypical, physiological and molecular approaches. APC7OE plants showed improved growth of vegetative organs, earlier flowering and increased photosynthetic efficiency, CO2 assimilation and productivity, compared with Col-0 control plants. Conversely, APC7-CTOE plants showed reduced susceptibility to both RNA and DNA viruses, along with an improvement in plant growth, although not surpassing APC7OE plants. Altogether, the data provide evidence for the role of the AtAPC7 in regulating cell division, expansion and differentiation, accompanied by an increase in photosynthetic capacity, resulting in enhanced plant biomass and seed yield. AtAPC7-CT might reduce growth-defence trade-offs, enabling plants to simultaneously defend themselves while promoting better growth. Our findings highlight the multifunctional role of AtAPC7, unveiling the potential of its orthologous genes as valuable biotechnological tools in important crops.

Discovering novel genomic regions explaining adaptation of bread wheat to conservation agriculture through GWAS

To sustainably increase wheat yield to meet the growing world population's food demand in the face of climate change, Conservation Agriculture (CA) is a promising approach. Still, there is a lack of genomic studies investigating the genetic basis of crop adaptation to CA. To dissect the genetic architecture of 19 morpho-physiological traits that could be involved in the enhanced adaptation and performance of genotypes under CA, we performed GWAS to identify MTAs under four contrasting production regimes viz., conventional tillage timely sown (CTTS), conservation agriculture timely sown (CATS), conventional tillage late sown (CTLS) and conservation agriculture late sown (CALS) using an association panel of 183 advanced wheat breeding lines along with 5 checks. Traits like Phi2 (Quantum yield of photosystem II; CATS:0.37, CALS: 0.31), RC (Relative chlorophyll content; CATS:55.51, CALS: 54.47) and PS1 (Active photosystem I centers; CATS:2.45, CALS: 2.23) have higher mean values in CA compared to CT under both sowing times. GWAS identified 80 MTAs for the studied traits across four production environments. The phenotypic variation explained (PVE) by these QTNs ranged from 2.15 to 40.22%. Gene annotation provided highly informative SNPs associated with Phi2, NPQ (Quantum yield of non-photochemical quenching), PS1, and RC which were linked with genes that play crucial roles in the physiological adaptation under both CA and CT. A highly significant SNP AX94651261 (9.43% PVE) was identified to be associated with Phi2, while two SNP markers AX94730536 (30.90% PVE) and AX94683305 (16.99% PVE) were associated with NPQ. Identified QTNs upon validation can be used in marker-assisted breeding programs to develop CA adaptive genotypes.

CsRAXs negatively regulate leaf size and fruiting ability through auxin glycosylation in cucumber

Leaves are the main photosynthesis organ that directly determines crop yield and biomass. Dissecting the regulatory mechanism of leaf development is crucial for food security and ecosystem turn-over. Here, we identified the novel function of R2R3-MYB transcription factors CsRAXs in regulating cucumber leaf size and fruiting ability. Csrax5 single mutant exhibited enlarged leaf size and stem diameter, and Csrax1/2/5 triple mutant displayed further enlargement phenotype. Overexpression of CsRAX1 or CsRAX5 gave rise to smaller leaf and thinner stem. The fruiting ability of Csrax1/2/5 plants was significantly enhanced, while that of CsRAX5 overexpression lines was greatly weakened. Similarly, cell number and free auxin level were elevated in mutant plants while decreased in overexpression lines. Biochemical data indicated that CsRAX1/5 directly promoted the expression of auxin glucosyltransferase gene CsUGT74E2. Therefore, our data suggested that CsRAXs function as repressors for leaf size development by promoting auxin glycosylation to decrease free auxin level and cell division in cucumber. Our findings provide new gene targets for cucumber breeding with increased leaf size and crop yield.

Petal size is controlled by the MYB73/TPL/HDA19-miR159-CKX6 module regulating cytokinin catabolism in Rosa hybrida

The size of plant lateral organs is determined by well-coordinated cell proliferation and cell expansion. Here, we report that miR159, an evolutionarily conserved microRNA, plays an essential role in regulating cell division in rose (Rosa hybrida) petals by modulating cytokinin catabolism. We uncover that Cytokinin Oxidase/Dehydrogenase6 (CKX6) is a target of miR159 in petals. Knocking down miR159 levels results in the accumulation of CKX6 transcripts and earlier cytokinin clearance, leading to a shortened cell division period and smaller petals. Conversely, knocking down CKX6 causes cytokinin accumulation and a prolonged developmental cell division period, mimicking the effects of exogenous cytokinin application. MYB73, a R2R3-type MYB transcription repressor, recruits a co-repressor (TOPLESS) and a histone deacetylase (HDA19) to form a suppression complex, which regulates MIR159 expression by modulating histone H3 lysine 9 acetylation levels at the MIR159 promoter. Our work sheds light on mechanisms for ensuring the correct timing of the exit from the cell division phase and thus organ size regulation by controlling cytokinin catabolism.

The MIO1-MtKIX8 module regulates the organ size in Medicago truncatula

Plant organ size is an important agronomic trait tightly related to crop yield. However, the molecular mechanisms underlying organ size regulation remain largely unexplored in legumes. We previously characterized a key regulator F-box protein MINI ORGAN1 (MIO1)/SMALL LEAF AND BUSHY1 (SLB1), which controls plant organ size in the model legume Medicago truncatula. In order to further dissect the molecular mechanism, MIO1 was used as the bait to screen its interacting proteins from a yeast library. Subsequently, a KIX protein, designated MtKIX8, was identified from the candidate list. The interaction between MIO1 and MtKIX8 was confirmed further by Y2H, BiFC, split-luciferase complementation and pull-down assays. Phylogenetic analyses indicated that MtKIX8 is highly homologous to Arabidopsis KIX8, which negatively regulates organ size. Moreover, loss-of-function of MtKIX8 led to enlarged leaves and seeds, while ectopic expression of MtKIX8 in Arabidopsis resulted in decreased cotyledon area and seed weight. Quantitative reverse-transcription PCR and in situ hybridization showed that MtKIX8 is expressed in most developing organs. We also found that MtKIX8 serves as a crucial molecular adaptor, facilitating interactions with BIG SEEDS1 (BS1) and MtTOPLESS (MtTPL) proteins in M. truncatula. Overall, our results suggest that the MIO1-MtKIX8 module plays a significant and conserved role in the regulation of plant organ size. This module could be a good target for molecular breeding in legume crops and forages.

Genome-wide identification and expression analysis of anaphase promoting complex/cyclosome (APC/C) in rose

The anaphase promoting complex/cyclosome (APC/C) is a large multi-subunit complex, regulating plant development and cell cycle. In plants, the APC/C gene family has been identified in Arabidopsis, rice, and maize. The APC/Cs in rose has not yet been reported. In this study, a total of 19 APC/C genes were identified in rose. Furthermore, we also investigated phylogenetic relationships, chromosomal distribution, gene structure, motif analysis, promoter sequence analysis and expression pattern of RhAPC/C genes. Synteny analysis indicated that AtAPC/Cs and RhAPC/Cs show a high degree of conservation. RhAPC/C promoters contains numerous cis-elements involved in plant morphogenesis, hormone response and stress response. Based on the transcription of RhAPC/Cs in different tissues and developmental stages, it appears that RhAPC/Cs may play a variety of roles in rose growth and development. RhAPC/Cs have limitations in the time and space during which they respond to hormones and abiotic stress. RhAPC5, RhAPC11d, RhAPC13a and RhAPC13c may play a role in rose responding to abiotic stress. The expression of RhAPC10 was altered by infection with fungal pathogen. Our study will serve as a basis for determining the functional role of APC/C genes in roses and help future research on woody plants.

Unlocking the molecular basis of wheat straw composition and morphological traits through multi-locus GWAS

BACKGROUND

Rapid reductions in emissions from fossil fuel burning are needed to curb global climate change. Biofuel production from crop residues can contribute to reducing the energy crisis and environmental deterioration. Wheat is a renewable source for biofuels owing to the low cost and high availability of its residues. Thus, identifying candidate genes controlling these traits is pivotal for efficient biofuel production. Here, six multi-locus genome-wide association (ML-GWAS) models were applied using 185 tetraploid wheat accessions to detect quantitative trait nucleotides (QTNs) for fifteen traits associated with biomass composition.

RESULTS

Among the 470 QTNs, only 72 identified by at least two models were considered as reliable. Among these latter, 16 also showed a significant effect on the corresponding trait (p.value < 0.05). Candidate genes survey carried out within 4 Mb flanking the QTNs, revealed putative biological functions associated with lipid transfer and metabolism, cell wall modifications, cell cycle, and photosynthesis. Four genes encoded as Cellulose Synthase (CeSa), Anaphase promoting complex (APC/C), Glucoronoxylan 4-O Methyltransferase (GXM) and HYPONASTIC LEAVES1 (HYL1) might be responsible for an increase in cellulose, and natural and acid detergent fiber (NDF and ADF) content in tetraploid wheat. In addition, the SNP marker RFL_Contig3228_2154 associated with the variation in stem solidness (Q.Scsb-3B) was validated through two molecular methods (High resolution melting; HRM and RNase H²-dependent PCR; rhAMP).

CONCLUSIONS

The study provides new insights into the genetic basis of biomass composition traits on tetraploid wheat. The application of six ML-GWAS models on a panel of diverse wheat genotypes represents an efficient approach to dissect complex traits with low heritability such as wheat straw composition. The discovery of genes/genomic regions associated with biomass production and straw quality parameters is expected to accelerate the development of high-yielding wheat varieties useful for biofuel production.

Effect of the At-CDC27a gene on Nicotiana benthamiana phenotype and accumulation of recombinant proteins

In this study the anaphase promoting complex subunit CDC27a from Arabidopsis thaliana was introduced in the genome of Nicotiana benthamiana by Agrobacterium tumefaciens. The presence of the At-CDC27a gene facilitates plant biomass production. Compared to wild type N. benthamiana the leaf mass fraction of the best performing transgenic line At-CDC27a-29 was increased up to 154%. The positive effect of the At-CDC27a expression on leaf biomass accumulation was accompanied by an enlarged total leaf area. Furthermore, the ectopic expression of the At-CDC27a also affected cellular conditions for the production of foreign proteins delivered by the TRBO vector. In comparison to the non-transgenic control, the protein accumulation in the At-CDC27a-29 plant host increased up to 146% for GFP and up to 181% for scFv-TM43-E10. Collectively, the modified N. benthamiana plants developed in this study might be useful to improve the yield of recombinant proteins per biomass unit in closed facilities.

The role of APC/C in cell cycle dynamics, growth and development in cereal crops

Cereal crops can be considered the basis of human civilization. Thus, it is not surprising that these crops are grown in larger quantities worldwide than any other food supply and provide more energy to humankind than any other provision. Additionally, attempts to harness biomass consumption continue to increase to meet human energy needs. The high pressures for energy will determine the demand for crop plants as resources for biofuel, heat, and electricity. Thus, the search for plant traits associated with genetic increases in yield is mandatory. In multicellular organisms, including plants, growth and development are driven by cell division. These processes require a sequence of intricated events that are carried out by various protein complexes and molecules that act punctually throughout the cycle. Temporal controlled degradation of key cell division proteins ensures a correct onset of the different cell cycle phases and exit from the cell division program. Considering the cell cycle, the Anaphase-Promoting Complex/Cyclosome (APC/C) is an important conserved multi-subunit ubiquitin ligase, marking targets for degradation by the 26S proteasome. Studies on plant APC/C subunits and activators, mainly in the model plant Arabidopsis, revealed that they play a pivotal role in several developmental processes during growth. However, little is known about the role of APC/C in cereal crops. Here, we discuss the current understanding of the APC/C controlling cereal crop development.

An Arabidopsis Retention and Splicing complex regulates root and embryo development through pre-mRNA splicing

Pre-mRNA splicing is an important step in the posttranscriptional processing of transcripts and a key regulator of development. The heterotrimeric retention and splicing (RES) complex plays vital roles in the growth and development of yeast, zebrafish, and humans by mediating pre-mRNA splicing of multiple genes. However, whether the RES complex is conserved in plants and what specific functions it has remain unknown. In this study, we identified Arabidopsis (Arabidopsis thaliana) BUD13 (AtBUD13), GROWTH, DEVELOPMENT AND SPLICING 1 (GDS1), and DAWDLE (DDL) as the counterparts of the yeast RES complex subunits Bud site selection protein 13 (Bud13), U2 snRNP component Snu17 (Snu17), and Pre-mRNA leakage protein 1, respectively. Moreover, we showed that RES is an ancient complex evolutionarily conserved in eukaryotes. GDS1 directly interacts with both AtBUD13 and DDL in nuclear speckles. The BUD13 domain of AtBUD13 and the RNA recognition motif domain of GDS1 are necessary and sufficient for AtBUD13-GDS1 interaction. Mutants of AtBUD13, GDS1, and DDL failed to properly splice multiple genes involved in cell proliferation and showed defects in early embryogenesis and root development. In addition, we found that GDS1 and DDL interact, respectively, with the U2 small nuclear ribonucleoproteins auxiliary factor AtU2AF65B and the NineTeen Complex-related splicing factor SKIP, which are essential for early steps of spliceosome assembly and recognition of splice sites. Altogether, our work reveals that the Arabidopsis RES complex is important for root and early embryo development by modulating pre-mRNA splicing.

The spinach YY genome reveals sex chromosome evolution, domestication, and introgression history of the species

Background

Spinach (Spinacia oleracea L.) is a dioecious species with an XY sex chromosome system, but its Y chromosome has not been fully characterized. Our knowledge about the history of its domestication and improvement remains limited.

Results

A high-quality YY genome of spinach is assembled into 952 Mb in six pseudo-chromosomes. By a combination of genetic mapping, Genome-Wide Association Studies, and genomic analysis, we characterize a 17.42-Mb sex determination region (SDR) on chromosome 1. The sex chromosomes of spinach evolved when an insertion containing sex determination genes occurred, followed by a large genomic inversion about 1.98 Mya. A subsequent burst of SDR-specific repeats (0.1–0.15 Mya) explains the large size of this SDR. We identify a Y-specific gene, NRT1/PTR 6.4 which resides in this insertion, as a strong candidate for the sex determination or differentiation factor. Resequencing of 112 spinach genomes reveals a severe domestication bottleneck approximately 10.87 Kya, which dates the domestication of spinach 7000 years earlier than the archeological record. We demonstrate that a strong selection signal associated with internode elongation and leaf area expansion is associated with domestication of edibility traits in spinach. We find that several strong genomic introgressions from the wild species Spinacia turkestanica and Spinacia tetrandra harbor desirable alleles of genes related to downy mildew resistance, frost resistance, leaf morphology, and flowering-time shift, which likely contribute to spinach improvement.

Conclusions

Analysis of the YY genome uncovers evolutionary forces shaping nascent sex chromosome evolution in spinach. Our findings provide novel insights about the domestication and improvement of spinach.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13059-022-02633-x.

At-CycD2 Enhances Accumulation of Above-Ground Biomass and Recombinant Proteins in Transgenic Nicotiana benthamiana Plants

Transient expression in Nicotiana benthamiana holds great potential for recombinant protein manufacturing due to its advantages in terms of speed and yield compared to stably transformed plants. To continue improving the quantity of recombinant proteins the plant host will need to be modified at both plant and cellular levels. In attempt to increase leaf mass fraction, we transformed N. benthamiana with the At-CycD2 gene, a positive regulator of the cell cycle. Phenotypic characterization of the T₁ progeny plants revealed their accelerated above-ground biomass accumulation and enhanced rate of leaf initiation. In comparison to non-transgenic control the best performing line At-CycD2-15 provided 143 and 140% higher leaf and stem biomass fractions, respectively. The leaf area enlargement of the At-CycD2-15 genotype was associated with the increase of epidermal cell number compensated by slightly reduced cell size. The production capacity of the At-CycD2-15 transgenic line was superior to that of the non-transgenic N. benthamiana. The accumulation of transiently expressed GFP and scFv-TM43-E10 proteins per unit biomass was increased by 138.5 and 156.7%, respectively, compared to the wild type. With these results we demonstrate the potential of cell cycle regulator gene At-CycD2 to modulate both plant phenotype and intracellular environment of N. benthamiana for enhanced recombinant protein yield.

SMALL LEAF AND BUSHY1 controls organ size and lateral branching by modulating the stability of BIG SEEDS1 in Medicago truncatula

Organ size is a major agronomic trait that determines grain yield and biomass production in crops. However, the molecular mechanisms controlling organ size, especially in legumes, are poorly understood. Using forward genetic approaches in a Tnt1 insertion mutant population of the model legume Medicago truncatula, we identified SMALL LEAF AND BUSHY1 (SLB1), which is required for the control of organ size and lateral branching. Loss of function of SLB1 led to reduced leaf and flower size but increased lateral branch formation in M. truncatula. SLB1 encodes an F-box protein, an orthologue of Arabidopsis thaliana STERILE APETALA (SAP), that forms part of an SKP1/Cullin/F-box E3 ubiquitin ligase complex. Biochemical and genetic analyses revealed that SLB1 controls M. truncatula organ growth and lateral branching by modulating the stability of BIG SEEDS1 (BS1). Moreover, the overexpression of SLB1 increased seed and leaf size in both M. truncatula and soybean (Glycine max), indicating functional conservation. Our findings revealed a novel mechanism by which SLB1 targets BS1 for degradation to regulate M. truncatula organ size and shoot branching, providing a new genetic tool for increasing seed yield and biomass production in crop and forage legumes.

Enhanced foreign protein accumulation in Nicotiana benthamiana leaves co-infiltrated with a TMV vector and plant cell cycle regulator genes

In this short communication, we report that the cell cycle checkpoint genes At-CycD2 and At-CDC27a from Arabidopsis thaliana enhance the transient heterologous protein expression in Nicotiana benthamiana. We selected a well-studied and widely used virus expression vector based on TMV for the delivery of recombinant proteins into the host plant. Co-infiltration of TMV-gfp and binary expression vectors carrying the At-CycD2 and At-CDC27a genes, respectively, resulted in enhanced GFP fluorescence in agroinoculated leaves. These findings corresponded with the observation of (1) higher mRNA levels for TMV and gfp and (2) increased GFP protein accumulation. Furthermore, by co-delivery of the TMV-scFv-TM43-E10 and At-CycD2/At-CDC27a expressing constructs we observed an enhanced amount of the scFv-TM43-E10 antibody fragment compared to the delivery of the TMV-scFv-TM43-E10 alone. We anticipate that this finding might be adapted for enhancing foreign protein production in N. benthamiana as the host plant.

Transcriptomic comparison reveals genetic variation potentially underlying seed developmental evolution of soybeans

Soybean (Glycine max) was domesticated from its wild relative Glycine soja. However, the genetic variations underlying soybean domestication are not well known. Comparative transcriptomics revealed that a small portion of the orthologous genes might have been fast evolving. In contrast, three gene expression clusters were identified as divergent by their expression patterns, which occupied 37.44% of the total genes, hinting at an essential role for gene expression alteration in soybean domestication. Moreover, the most divergent stage in gene expression between wild and cultivated soybeans occurred during seed development around the cotyledon stage (15 d after fertilization, G15). A module in which the co-expressed genes were significantly down-regulated at G15 of wild soybeans was identified. The divergent clusters and modules included substantial differentially expressed genes (DEGs) between wild and cultivated soybeans related to cell division, storage compound accumulation, hormone response, and seed maturation processes. Chromosomal-linked DEGs, quantitative trait loci controlling seed weight and oil content, and selection sweeps revealed candidate DEGs at G15 in the fruit-related divergence of G. max and G. soja. Our work establishes a transcriptomic selection mechanism for altering gene expression during soybean domestication, thus shedding light on the molecular networks underlying soybean seed development and breeding strategy.

STERILE APETALA modulates the stability of a repressor protein complex to control organ size in Arabidopsis thaliana

Organ size control is of particular importance for developmental biology and agriculture, but the mechanisms underlying organ size regulation remain elusive in plants. Meristemoids, which possess stem cell-like properties, have been recognized to play important roles in leaf growth. We have recently reported that the Arabidopsis F-box protein STERILE APETALA (SAP)/SUPPRESSOR OF DA1 (SOD3) promotes meristemoid proliferation and regulates organ size by influencing the stability of the transcriptional regulators PEAPODs (PPDs). Here we demonstrate that KIX8 and KIX9, which function as adaptors for the corepressor TOPLESS and PPD, are novel substrates of SAP. SAP interacts with KIX8/9 and modulates their protein stability. Further results show that SAP acts in a common pathway with KIX8/9 and PPD to control organ growth by regulating meristemoid cell proliferation. Thus, these findings reveal a molecular mechanism by which SAP targets the KIX-PPD repressor complex for degradation to regulate meristemoid cell proliferation and organ size.

Organ size is coordinately regulated by cell proliferation and cell expansion; however, the mechanisms of organ size control are still poorly understood. We have previously demonstrated that the Arabidopsis F-box protein STERILE APETALA (SAP)/SUPPRESSOR OF DA1 (SOD3) controls organ size by promoting meristemoid proliferation. SAP functions as part of a SKP1/Cullin/F-box (SCF) E3 ubiquitin ligase complex and modulates the stability of the transcriptional regulators PEAPODs (PPDs) to control organ growth. Here we show that KIX8 and KIX9 are novel substrates of SAP. KIX8 and KIX9 have been shown to form a transcriptional repressor complex with PPD and TOPLESS (TPL) to regulate leaf growth. We found that SAP interacts with KIX8/9 in vitro and in vivo, and modulates their protein stability. Further analyses indicate that SAP acts in a common pathway with KIX8/9 and PPD to control meristemoid proliferation and organ growth. These findings reveal that SAP regulates organ size by targeting the KIX-PPD repressor complex for degradation.

OLIGOCELLULA1/HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES15 Promotes Cell Proliferation With HISTONE DEACETYLASE9 and POWERDRESS During Leaf Development in Arabidopsis thaliana

Organ size regulation is dependent on the precise spatial and temporal regulation of cell proliferation and cell expansion. A number of transcription factors have been identified that play a key role in the determination of aerial lateral organ size, but their functional relationship to various chromatin modifiers has not been well understood. To understand how leaf size is regulated, we previously isolated the oligocellula1 (oli1) mutant of Arabidopsis thaliana that develops smaller first leaves than the wild type (WT) mainly due to a reduction in the cell number. In this study, we further characterized oli1 leaf phenotypes and identified the OLI1 gene as well as interaction partners of OLI1. Detailed characterizations of leaf development suggested that the cell proliferation rate in oli1 leaf primordia is lower than that in the WT. In addition, oli1 was associated with a slight delay of the progression from the juvenile to adult phases of leaf traits. A classical map-based approach demonstrated that OLI1 is identical to HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES15 (HOS15). HOS15/OLI1 encodes a homolog of human transducin β-like protein1 (TBL1). TBL1 forms a transcriptional repression complex with the histone deacetylase (HDAC) HDAC3 and either nuclear receptor co-repressor (N-CoR) or silencing mediator for retinoic acid and thyroid receptor (SMRT). We found that mutations in HISTONE DEACETYLASE9 (HDA9) and a switching-defective protein 3, adaptor 2, N-CoR, and transcription factor IIIB-domain protein gene, POWERDRESS (PWR), showed a small-leaf phenotype similar to oli1. In addition, hda9 and pwr did not further enhance the oli1 small-leaf phenotype, suggesting that these three genes act in the same pathway. Yeast two-hybrid assays suggested physical interactions, wherein PWR probably bridges HOS15/OLI1 and HDA9. Earlier studies suggested the roles of HOS15, HDA9, and PWR in transcriptional repression. Consistently, transcriptome analyses showed several genes commonly upregulated in the three mutants. From these findings, we propose a possibility that HOS15/OLI1, PWR, and HDA9 form an evolutionary conserved transcription repression complex that plays a positive role in the regulation of final leaf size.

F-Box Protein FBX92 Affects Leaf Size in Arabidopsis thaliana

F-box proteins are part of one of the largest families of regulatory proteins that play important roles in protein degradation. In plants, F-box proteins are functionally very diverse, and only a small subset has been characterized in detail. Here, we identified a novel F-box protein FBX92 as a repressor of leaf growth in Arabidopsis. Overexpression of AtFBX92 resulted in plants with smaller leaves than the wild type, whereas plants with reduced levels of AtFBX92 showed, in contrast, increased leaf growth by stimulating cell proliferation. Detailed cellular analysis suggested that AtFBX92 specifically affects the rate of cell division during early leaf development. This is supported by the increased expression levels of several cell cycle genes in plants with reduced AtFBX92 levels. Surprisingly, overexpression of the maize homologous gene ZmFBX92 in maize had no effect on plant growth, whereas ectopic expression in Arabidopsis increased leaf growth. Expression of a truncated form of AtFBX92 showed that the contrasting effects of ZmFBX92 and AtFBX92 gain of function in Arabidopsis are due to the absence of the F-box-associated domain in the ZmFBX92 gene. Our work reveals an additional player in the complex network that determines leaf size and lays the foundation for identifying putative substrates.

Transcriptomic profiling of taproot growth and sucrose accumulation in sugar beet (Beta vulgaris L.) at different developmental stages

In sugar beet (Beta vulgaris L.), taproot weight and sucrose content are the important determinants of yield and quality. However, high yield and low sucrose content are two tightly bound agronomic traits. The advances in next-generation sequencing technology and the publication of sugar beet genome have provided a method for the study of molecular mechanism underlying the regulation of these two agronomic traits. In this work, we performed comparative transcriptomic analyses in the high taproot yield cultivar SD13829 and the high sucrose content cultivar BS02 at five developmental stages. More than 50,000,000 pair-end clean reads for each library were generated. When taproot turned into the rapid growth stage at the growth stage of 82 days after emergence (DAE), eighteen enriched gene ontology (GO) terms, including cell wall, cytoskeleton, and enzyme linked receptor protein signaling pathway, occurred in both cultivars. Differentially expressed genes (DEGs) of paired comparison in both cultivars were enriched in the cell wall GO term. For pathway enrichment analyses of DEGs that were respectively generated at 82 DAE compared to 59 DAE (the earlier developmental stage before taproot turning into the rapid growth stage), plant hormone signal transduction pathway was enriched. At 82 DAE, the rapid enlarging stage of taproot, several transcription factor family members were up-regulated in both cultivars. An antagonistic expression of brassinosteroid- and auxin-related genes was also detected. In SD13829, the growth strategy was relatively focused on cell enlargement promoted by brassinosteroid signaling, whereas in BS02, it was relatively focused on secondarily cambial cell division regulated by cytokinin, auxin and brassinosteroid signaling. Taken together, our data demonstrate that the weight and sucrose content of taproot rely on its growth strategy, which is controlled by brassinosteroid, auxin, cytokinin, and gibberellin.

Superoxide serves as a putative signal molecule for plant cell division: overexpression of CaRLK1 promotes the plant cell cycle via accumulation of O2- and decrease in H2 O2

Reactive oxygen species (ROS) exert both positive and negative effects on plant growth and development and therefore receive a great deal of attention in current research. A hot pepper, Capsicum annuum receptor-like kinase 1 (CaRLK1) was ectopically expressed in Nicotiana tabacum BY-2 cell and Nicotiana benthamiana plants. This ectopic expression of CaRLK1 enhanced cell division and proliferation in both heterologous systems. Apparently, CaRLK1 is involved in controlling the cell cycle, possibly by inducing expressions of cyclin B1, cyclin D3, cyclin-dependent protein kinase 3, condensin complex subunit 2 and anaphase-promoting complex subunit 11 genes. CaRLK1 overexpression also increased transcript accumulation of NADPH oxidase genes, generation of O2- and catalase (CAT) activity/protein levels. In parallel, it decreased cellular H2 O2 levels and cell size. Treatment with Tiron or diphenyleneiodonium (DPI) both decreased the cell division rate and O2- concentrations, but increased cellular H2 O2 levels. Tobacco BY-2 cells overexpressing CaRLK1 were more sensitive to amino-1,2,4-triazole (3-AT), a CAT inhibitor, than control cells, suggesting that the increased H2 O2 levels may not function as a signal for cell division and proliferation. Overexpression of CaRLK1 stimulated progression of the cell cycle from G0 /G1 phase into the S phase. It is concluded that the CaRLK1 protein plays a pivotal role in controlling the level of O2- as signaling molecule which promotes cell division, concomitant with a reduction in H2 O2 by the induction of CAT activity/protein.

AtGRP3 Is Implicated in Root Size and Aluminum Response Pathways in Arabidopsis

AtGRP3 is a glycine-rich protein (GRP) from Arabidopsis thaliana shown to interact with the receptor-like kinase AtWAK1 in yeast, in vitro and in planta. In this work, phenotypic analyses using transgenic plants were performed in order to better characterize this GRP. Plants of two independent knockout alleles of AtGRP3 develop longer roots suggesting its involvement in root size determination. Confocal microscopy analysis showed an abnormal cell division and elongation in grp3-1 knockout mutants. Moreover, we also show that grp3-1 exhibits an enhanced Aluminum (Al) tolerance, a feature also described in AtWAK1 overexpressing plants. Together, these results implicate AtGRP3 function root size determination during development and in Al stress.

Behavior of Leaf Meristems and Their Modification

A major source of diversity in flowering plant form is the extensive variability of leaf shape and size. Leaf formation is initiated by recruitment of a handful of cells flanking the shoot apical meristem (SAM) to develop into a complex three-dimensional structure. Leaf organogenesis depends on activities of several distinct meristems that are established and spatiotemporally differentiated after the initiation of leaf primordia. Here, we review recent findings in the gene regulatory networks that orchestrate leaf meristem activities in a model plant Arabidopsis thaliana. We then discuss recent key studies investigating the natural variation in leaf morphology to understand how the gene regulatory networks modulate leaf meristems to yield a substantial diversity of leaf forms during the course of evolution.

Size control in plants--lessons from leaves and flowers

To achieve optimal functionality, plant organs like leaves and petals have to grow to a certain size. Beginning with a limited number of undifferentiated cells, the final size of an organ is attained by a complex interplay of cell proliferation and subsequent cell expansion. Regulatory mechanisms that integrate intrinsic growth signals and environmental cues are required to enable optimal leaf and flower development. This review focuses on plant-specific principles of growth reaching from the cellular to the organ level. The currently known genetic pathways underlying these principles are summarized and network connections are highlighted. Putative non-cell autonomously acting mechanisms that might coordinate plant-cell growth are discussed.

The effect of the unfolded protein response on the production of recombinant proteins in plants

Recombinant proteins are currently produced through a wide variety of host systems, including yeast, E. coli, insect and mammalian cells. One of the most recent systems developed uses plant cells. While considerable advances have been made in the yields and fidelity of plant-made recombinant proteins, many of these gains have arisen from the development of recombinant factors. This includes elements such as highly effective promoters and untranslated regions, deconstructed viral vectors, silencing inhibitors, and improved DNA delivery techniques. However, unlike other host systems, much of the work on recombinant protein production in plants uses wild-type hosts that have not been modified to facilitate recombinant protein expression. As such, there are still endogenous mechanisms functioning to maintain the health of the cell. The result is that these pathways, such as the unfolded protein response, can actively work to reduce recombinant protein production to maintain the integrity of the cell. This review examines how issues arising from the unfolded protein response have been addressed in other systems, and how these methods may be transferable to plant systems. We further identify several areas of host plant biology that present attractive targets for modification to facilitate recombinant protein production.

The ASH1-RELATED3 SET-domain protein controls cell division competence of the meristem and the quiescent center of the Arabidopsis primary root

The stem cell niche of the Arabidopsis (Arabidopsis thaliana) primary root apical meristem is composed of the quiescent (or organizing) center surrounded by stem (initial) cells for the different tissues. Initial cells generate a population of transit-amplifying cells that undergo a limited number of cell divisions before elongating and differentiating. It is unclear whether these divisions occur stochastically or in an orderly manner. Using the thymidine analog 5-ethynyl-2'-deoxyuridine to monitor DNA replication of cells of Arabidopsis root meristems, we identified a pattern of two, four, and eight neighboring cells with synchronized replication along the cortical, epidermal, and endodermal cell files, suggested to be daughters, granddaughters, and great-granddaughters of the direct progeny of each stem cell. Markers of mitosis and cytokinesis were not present in the region closest to the transition zone where the cells start to elongate, suggesting that great-granddaughter cells switch synchronously from the mitotic cell cycle to endoreduplication. Mutations in the stem cell niche-expressed ASH1-RELATED3 (ASHR3) gene, encoding a SET-domain protein conferring histone H3 lysine-36 methylation, disrupted this pattern of coordinated DNA replication and cell division and increased the cell division rate in the quiescent center. E2Fa/E2Fb transcription factors controlling the G1-to-S-phase transition regulate ASHR3 expression and bind to the ASHR3 promoter, substantiating a role for ASHR3 in cell division control. The reduced length of the root apical meristem and primary root of the mutant ashr3-1 indicate that synchronization of replication and cell divisions is required for normal root growth and development.

The cell-cycle interactome: a source of growth regulators?

When plants develop, cell proliferation and cell expansion are tightly controlled in order to generate organs with a determinate final size such as leaves. Several studies have demonstrated the importance of the cell proliferation phase for leaf growth, illustrating that cell-cycle regulation is crucial for correct leaf development. A large and complex set of interacting proteins that constitute the cell-cycle interactome controls the transition from one cell-cycle phase to another. Here, we review the current knowledge on cell-cycle regulators from this interactome affecting final leaf size when their expression is altered, mainly in Arabidopsis. In addition to the description of mutants of CYCLIN-DEPENDENT KINASES (CDKs), CYCLINS (CYCs), and their transcriptional and post-translational regulators, a phenotypic analysis of gain- and loss-of-function mutants for 27 genes encoding proteins that interact with cell-cycle proteins is presented. This compilation of information shows that when cell-cycle-related genes are mis-expressed, leaf growth is often altered and that, seemingly, three main trends appear to be crucial in the regulation of final organ size by cell-cycle-related genes: (i) cellular compensation; (ii) gene dosage; and (iii) correct transition through the G2/M phase by ANAPHASE PROMOTING COMPLEX/CYCLOSOME (APC/C) activation. In conclusion, this meta-analysis shows that the cell-cycle interactome is enriched in leaf growth regulators, and illustrates the potential to identify new leaf growth regulators among putative new cell-cycle regulators.

Selective protein degradation: a rheostat to modulate cell-cycle phase transitions

Plant growth control has become a major focus due to economic reasons and results from a balance of cell proliferation in meristems and cell elongation that occurs during differentiation. Research on plant cell proliferation over the last two decades has revealed that the basic cell-cycle machinery is conserved between human and plants, although specificities exist. While many regulatory circuits control each step of the cell cycle, the ubiquitin proteasome system (UPS) appears in fungi and metazoans as a major player. In particular, the UPS promotes irreversible proteolysis of a set of regulatory proteins absolutely required for cell-cycle phase transitions. Not unexpectedly, work over the last decade has brought the UPS to the forefront of plant cell-cycle research. In this review, we will summarize our knowledge of the function of the UPS in the mitotic cycle and in endoreduplication, and also in meiosis in higher plants.

Overexpression of the anaphase-promoting complex (APC) genes in Nicotiana tabacum promotes increasing biomass accumulation

The anaphase-promoting complex (APC) plays pivotal roles in cell cycle pathways related to plant development. In this study, we present evidence that overproduction of APC10 from Arabidopsis thaliana in tobacco (Nicotiana tabacum) plants promotes significant increases in biomass. Analyzes of plant's fresh and dried weight, root length, number of days to flower and number of seeds of plants overexpressing AtAPC10 verified an improved agronomic performance of the transgenic plants. Detailed analyzes of the leaf growth at the cellular level, and measurements of leaf cell number, showed that AtAPC10 also produce more cells, showing an enhancement of proliferation in these plants. In addition, crossing of plants overexpressing AtAPC10 and AtCDC27a resulted in a synergistic accumulation of biomass and these transgenic plants exhibited superior characteristics compared to the parental lines. The results of the present study suggest that transgenic plants expressing AtAPC10 and AtAPC10/AtCDC27a concomitantly are promising leads to develop plants with higher biomass.

The anaphase-promoting complex/cyclosome in control of plant development

Temporal controlled degradation of key cell division proteins ensures a correct onset of the different cell cycle phases and exit from the cell division program. In light of the cell cycle, the Anaphase-Promoting Complex/Cyclosome (APC/C) is an important conserved multi-subunit ubiquitin ligase, marking targets for degradation by the 26S proteasome. However, whereas the APC/C has been studied extensively in yeast and mammals, only in the last decade has the plant APC/C started to unveil its secrets. Research results have shown the importance of the APC/C core complex and its activators during gametogenesis, growth, hormone signaling, symbiotic interactions, and endoreduplication onset. In addition, recently, the first plant APC/C inhibitors have been reported, allowing a fine-tuning of APC/C activity during the cell cycle. Together with the identification of the first APC/C targets, a picture emerges of APC/C activity being essential for many different developmental processes.

Identification of ANAPC13 gene polymorphisms associated with body measurement traits in Bos taurus

Body measurement traits, influenced by genes and environmental factors, play numerous important roles in the value assessment of productivity and economy. There has been some indication that ANAPC13 influences adult height. We used PCR-SSCP and DNA sequencing technology to identify polymorphisms in the ANAPC13 gene. A polymorphism in intron 1 (A > G at base 17) was identified and an additional polymorphic site (C > T at base 42) was also uncovered, which accompanied the previous polymorphism in more than 98% of the subjects. The two novel polymorphisms in exon 1 were assayed and potential associations with body measurement traits were evaluated in 404 individuals. Three genotypes were detected in the study group, named AACC, AGCT and GGTT. Significant differences were observed between genotypes AACC and AGCT for body length, withers height, hip height, hip width, heart girth, pin bone width. However, no associations were found among any genotypes and chest depth. We conclude that polymorphisms and mutations in non-coding regions of the ANAPC13 gene significantly affect body measurement traits.

Leaf size control: complex coordination of cell division and expansion

Size control of multicellular organisms poses a longstanding biological question that has always fascinated scientists. Currently the question is far from being resolved because of the complexity of and interconnection between cell division and cell expansion, two different events necessary to form a mature organ. Because of the importance of plants for food and renewable energy sources, dissecting the genetic networks underlying plant growth and organ size is becoming a high priority in plant science worldwide. Here, we review the current understanding of the cellular and molecular mechanisms that govern leaf organ size and discuss future prospects on research aiming at understanding organ size regulation.

Abnormal endosperm development causes female sterility in rice insertional mutant OsAPC6

A T-DNA insertional mutant OsAPC6 of rice, with gibberellic acid insensitivity and reduced height, had up to 45% reduced seed set. The insertion occurred on chromosome 3 of rice in the gene encoding one of the subunits of anaphase promoting complex/Cyclosome APC6. The primary mother cells of the mutant plants had normal meiosis, male gametophyte development and pollen viability. Confocal laser scanning microscopic (CLSM) studies of megagametophyte development showed abnormal mitotic divisions with reduced number or total absence of polar nuclei in about 30-35% megagametophytes of OsAPC6 mutant leading to failure of endosperm and hence embryo and seed development. Abnormal female gametophyte development, high sterility and segregation of tall and gibberellic acid sensitive plants without selectable marker Hpt in the selfed progeny of OsAPC6 mutant plants indicate that the mutant could be maintained in heterozygous condition. The abnormal mitotic divisions during megagametogenesis could be attributed to the inactivation of the APC6/CDC16 of anaphase promoting complex of rice responsible for cell cycle progression during megagametogenesis. Functional validation of the candidate gene through transcriptome profiling and RNAi is in progress.

Molecular diagnosis of Papaya meleira virus (PMeV) from leaf samples of Carica papaya L. using conventional and real-time RT-PCR

Papaya meleira virus (PMeV) is the causal agent of papaya sticky disease. This study describes two methods for molecular diagnosis of PMeV using conventional and real-time PCR. These methods were shown to be more efficient than current methods of viral detection using extraction of PMeV dsRNA and observation of symptoms in the field. The methods described here were used to evaluate the effect of inoculation of papaya plants with purified PMeV dsRNA on the progress of PMeV infection. A single inoculation with PMeV dsRNA was observed to delay the progress of the virus infection by several weeks. The possibility of vertical transmission of PMeV was also investigated. No evidence was found for PMeV transmission through seeds collected from diseased fruit. The implications of these results for the epidemiology of PMeV and the management of papaya sticky disease are discussed.

NIMA-related kinase NEK6 affects plant growth and stress response in Arabidopsis

The NIMA-related kinases (NEKs) are a family of serine/threonine kinases involved largely in cell cycle control in fungi, mammals and other eukaryotes. In Arabidopsis, NEK6 is involved in the regulation of epidermal cell morphogenesis. However, other roles of NEK6 in plants are less well understood. Here we report functions of NEK6 in plant growth, development and stress responses in Arabidopsis. NEK6 transcripts and proteins are induced by ethylene precursor ACC and salt stress. Expression of other NEK genes except NEK5 is also responsive to the two treatments. Overexpression and mutant analysis disclose that the NEK6 gene increases rosette growth, seed yield and lateral root formation. However, NEK6 appears to play a negative role in the control of seed size. The gene also promotes plant tolerance to salt stress and osmotic stress in its overexpressing plants. The NEK6 gene may achieve its function through suppression of ethylene biosynthesis and activation of CYCB1;1 and CYCA3;1 expression. Our present study reveals new functions of the NEK6 gene in plant growth and stress tolerance, and manipulation of NEK6 may improve important agronomic traits in crop plants.

The APC/C subunit 10 plays an essential role in cell proliferation during leaf development

The largest E3 ubiquitin-ligase complex, known as anaphase-promoting complex/cyclosome (APC/C), regulates the proteolysis of cell cycle regulators such as CYCLIN B and SECURIN that are essential for sister-chromatid separation and exit from mitosis. Despite its importance, the role of APC/C in plant cells and the regulation of its activity during cell division remain poorly understood. Here, the Arabidopsis thaliana APC/C subunit APC10 was characterized and shown to functionally complement an apc10 yeast mutant. The APC10 protein was located in specific nuclear bodies, most probably resulting from its association with the proteasome complex. An apc10 Arabidopsis knockout mutant strongly impaired female gametogenesis. Surprisingly, constitutive overexpression of APC10 enhanced leaf size. Through kinematic analysis, the increased leaf size was found to be due to enhanced rates of cell division during the early stages of leaf development and, at the molecular level, by increased APC/C activity as measured by an amplification of the proteolysis rate of the mitotic cyclin, CYCB1;1.

Role of transgenic plants in agriculture and biopharming

At present, environmental degradation and the consistently growing population are two main problems on the planet earth. Fulfilling the needs of this growing population is quite difficult from the limited arable land available on the globe. Although there are legal, social and political barriers to the utilization of biotechnology, advances in this field have substantially improved agriculture and human life to a great extent. One of the vital tools of biotechnology is genetic engineering (GE) which is used to modify plants, animals and microorganisms according to desired needs. In fact, genetic engineering facilitates the transfer of desired characteristics into other plants which is not possible through conventional plant breeding. A variety of crops have been engineered for enhanced resistance to a multitude of stresses such as herbicides, insecticides, viruses and a combination of biotic and abiotic stresses in different crops including rice, mustard, maize, potato, tomato, etc. Apart from the use of GE in agriculture, it is being extensively employed to modify the plants for enhanced production of vaccines, hormones, etc. Vaccines against certain diseases are certainly available in the market, but most of them are very costly. Developing countries cannot afford the disease control through such cost-intensive vaccines. Alternatively, efforts are being made to produce edible vaccines which are cheap and have many advantages over the commercialized vaccines. Transgenic plants generated for this purpose are capable of expressing recombinant proteins including viral and bacterial antigens and antibodies. Common food plants like banana, tomato, rice, carrot, etc. have been used to produce vaccines against certain diseases like hepatitis B, cholera, HIV, etc. Thus, the up- and down-regulation of desired genes which are used for the modification of plants have a marked role in the improvement of genetic crops. In this review, we have comprehensively discussed the role of genetic engineering in generating transgenic lines/cultivars of different crops with improved nutrient quality, biofuel production, enhanced production of vaccines and antibodies, increased resistance against insects, herbicides, diseases and abiotic stresses as well as the safety measures for their commercialization.

A role for the anaphase promoting complex in hormone regulation

To increase our knowledge of anaphase promoting complex (APC/C) function during plant development, we characterized an Arabidopsis thaliana T-DNA-insertion line where the T-DNA fell within the 5' regulatory region of the APC10 gene. The insert disrupted endogenous expression, resulting in overexpression of APC10 mRNA from the T-DNA- internal CaMV 35S promoter, and increased APC10 protein. Overexpression of APC10 produced phenotypes resembling those of known auxin and ethylene mutants, and increased expression of two tested auxin-regulated genes, small auxin up RNA (SAUR) 15 and SAUR24. Taken together, our data suggests that elevated APC10 likely mimics auxin and ethylene sensitive phenotypes, expanding our understanding of proteolytic processes in hormone regulation of plant development.

Developmental control of endocycles and cell growth in plants

Timely progression of the mitotic cell cycle is central for growth and development of plant organs. Many cell types in plants also enter an alternative cell cycle called the endoreduplication cycle or endocycle in which cells increase their ploidy through repeated rounds of chromosomal replication without cell divisions. The transition from the mitotic cycle into the endocycle often coincides with the initiation of cell expansion and cell differentiation, and strong correlations between final ploidy level and cell size have been reported in many plant species. Recent studies have begun to unveil how developmental signals modulate entry and exit of the endocycle through both transcriptional and post-transcriptional mechanisms. An increase in ploidy by endocycles is not an ultimate determinant of plant cell size and it is likely that it sets the maximum capacity for future cellular growth.