Altered expression of wheat AINTEGUMENTA homolog, WANT-1, in pistil and pistil-like transformed stamen of an alloplasmic line with Aegilops crassa cytoplasm

Genome-wide characterization of AINTEGUMENTA-LIKE family in Medicago truncatula reveals the significant roles of AINTEGUMENTAs in leaf growth

AINTEGUMENTA-LIKE (AIL) transcription factors are widely studied and play crucial roles in plant growth and development. However, the functions of the AIL family in legume species are largely unknown. In this study, 11 MtAIL genes were identified in the model legume Medicago truncatula, of which four of them are MtANTs. In situ analysis showed that MtANT1 was highly expressed in the shoot apical meristem (SAM) and leaf primordium. Characterization of mtant1 mtant2 mtant3 mtant4 quadruple mutants and MtANT1-overexpressing plants revealed that MtANTs were not only necessary but also sufficient for the regulation of leaf size, and indicated that they mainly function in the regulation of cell proliferation during secondary morphogenesis of leaves in M. truncatula. This study systematically analyzed the MtAIL family at the genome-wide level and revealed the functions of MtANTs in leaf growth. Thus, these genes may provide a potential application for promoting the biomass of legume forages.

Genetic and Molecular Control of Floral Organ Identity in Cereals

Grasses represent a major family of monocots comprising mostly cereals. When compared to their eudicot counterparts, cereals show a remarkable morphological diversity. Understanding the molecular basis of floral organ identity and inflorescence development is crucial to gain insight into the grain development for yield improvement purposes in cereals, however, the exact genetic mechanism of floral organogenesis remains elusive due to their complex inflorescence architecture. Extensive molecular analyses of Arabidopsis and other plant genera and species have established the ABCDE floral organ identity model. According to this model, hierarchical combinatorial activities of A, B, C, D, and E classes of homeotic genes regulate the identity of different floral organs with partial conservation and partial diversification between eudicots and cereals. Here, we review the developmental role of A, B, C, D, and E gene classes and explore the recent advances in understanding the floral development and subsequent organ specification in major cereals with reference to model plants. Furthermore, we discuss the evolutionary relationships among known floral organ identity genes. This comparative overview of floral developmental genes and associated regulatory factors, within and between species, will provide a thorough understanding of underlying complex genetic and molecular control of flower development and floral organ identity, which can be helpful to devise innovative strategies for grain yield improvement in cereals.

Comparative proteomic analysis of multi-ovary wheat under heterogeneous cytoplasm suppression

BACKGROUND

DUOII is a multi-ovary wheat (Triticum aestivum L.) line with two or three pistils and three stamens in each floret. The multi-ovary trait of DUOII is controlled by a dominant gene, whose expression can be suppressed by the heterogeneous cytoplasm of TeZhiI (TZI), a line with the nucleus of common wheat and the cytoplasm of Aegilops. Crosses between female DUOII plants and male TZI plants resulted in multi-ovary F₁s; whereas, the reciprocal crosses resulted in mono-ovary F₁s. Although the multi-ovary trait is inherited as single trait controlled by a dominant allele in lines with a Triticum cytoplasm, the mechanism by which the special heterogeneous cytoplasm suppresses the expression of multi-ovary is not well understood.

RESULTS

Observing the developmental process, we found that the critical stage of additional pistil primordium development was when the young spikes were 2-6 mm long. Then, we compared the quantitative proteomic profiles of 2-6 mm long young spikes obtained from the reciprocal crosses between DUOII and TZI. A total of 90 differentially expressed proteins were identified and analyzed based on their biological functions. These proteins had obvious functional pathways mainly implicated in chloroplast metabolism, nuclear and cell division, plant respiration, protein metabolism, and flower development. Importantly, we identified two key proteins, Flowering Locus K Homology Domain and PEPPER, which are known to play an essential role in the specification of pistil organ identity. By drawing relationships between the 90 differentially expressed proteins, we found that these proteins revealed a complex network which is associated with multi-ovary gene expression under heterogeneous cytoplasmic suppression.

CONCLUSIONS

Our proteomic analysis has identified certain differentially expressed proteins in 2-6 mm long young spikes, which was the critical stage of additional primordium development. This paper provided a universal proteomic profiling involved in the cytoplasmic suppression of wheat floral meristems; and our findings have laid a solid foundation for further mechanistic studies on the underlying mechanisms that control the heterogeneous cytoplasm-induced suppression of the nuclear multi-ovary gene in wheat.

Cloning and Functional Analysis of MADS-box Genes, TaAG-A and TaAG-B, from a Wheat K-type Cytoplasmic Male Sterile Line

Wheat (Triticum aestivum L.) is a major crop worldwide. The utilization of heterosis is a promising approach to improve the yield and quality of wheat. Although there have been many studies on wheat cytoplasmic male sterility, its mechanism remains unclear. In this study, we identified two MADS-box genes from a wheat K-type cytoplasmic male sterile (CMS) line using homology-based cloning. These genes were localized on wheat chromosomes 3A and 3B and named TaAG-A and TaAG-B, respectively. Analysis of TaAG-A and TaAG-B expression patterns in leaves, spikes, roots, and stems of Chinese Spring wheat determined using quantitative RT-PCR revealed different expression levels in different tissues. TaAG-A had relatively high expression levels in leaves and spikes, but low levels in roots, while TaAG-B had relatively high expression levels in spikes and lower expression in roots, stems, and leaves. Both genes showed downregulation during the mononucleate to trinucleate stages of pollen development in the maintainer line. In contrast, upregulation of TaAG-B was observed in the CMS line. The transcript levels of the two genes were clearly higher in the CMS line compared to the maintainer line at the trinucleate stage. Overexpression of TaAG-A and TaAG-B in Arabidopsis resulted in phenotypes with earlier reproductive development, premature mortality, and abnormal buds, stamens, and stigmas. Overexpression of TaAG-A and TaAG-B gives rise to mutants with many deformities. Silencing TaAG-A and TaAG-B in a fertile wheat line using the virus-induced gene silencing (VIGS) method resulted in plants with green and yellow striped leaves, emaciated spikes, and decreased selfing seed set rates. These results demonstrate that TaAG-A and TaAG-B may play a role in male sterility in the wheat CMS line.

Transcriptome Analysis for Abnormal Spike Development of the Wheat Mutant dms

Background

Wheat (Triticum aestivum L.) spike development is the foundation for grain yield. We obtained a novel wheat mutant, dms, characterized as dwarf, multi-pistil and sterility. Although the genetic changes are not clear, the heredity of traits suggests that a recessive gene locus controls the two traits of multi-pistil and sterility in self-pollinating populations of the medium plants (M), such that the dwarf genotype (D) and tall genotype (T) in the progeny of the mutant are ideal lines for studies regarding wheat spike development. The objective of this study was to explore the molecular basis for spike abnormalities of dwarf genotype.

Results

Four unigene libraries were assembled by sequencing the mRNAs of the super-bulked differentiating spikes and stem tips of the D and T plants. Using integrative analysis, we identified 419 genes highly expressed in spikes, including nine typical homeotic genes of the MADS-box family and the genes TaAP2, TaFL and TaDL. We also identified 143 genes that were significantly different between young spikes of T and D, and 26 genes that were putatively involved in spike differentiation. The result showed that the expression levels of TaAP1-2, TaAP2, and other genes involved in the majority of biological processes such as transcription, translation, cell division, photosynthesis, carbohydrate transport and metabolism, and energy production and conversion were significantly lower in D than in T.

Conclusions

We identified a set of genes related to wheat floral organ differentiation, including typical homeotic genes. Our results showed that the major causal factors resulting in the spike abnormalities of dms were the lower expression homeotic genes, hormonal imbalance, repressed biological processes, and deficiency of construction materials and energy. We performed a series of studies on the homeotic genes, however the other three causal factors for spike abnormal phenotype of dms need further study.

Role of AINTEGUMENTA-like gene NtANTL in the regulation of tobacco organ growth

The Nicotiana tabacum AINTEGUMENTA-like gene (NtANTL), encoding one of AP2/ERF transcription factors, is a putative ortholog of the AtANT gene from Arabidopsis thaliana. In wild-type tobacco plants, the NtANTL gene was expressed in the actively dividing young flowers, shoot apices, and calluses, while the level of its mRNA increased considerably after treatment with exogenous 6-benzylaminopurine, indoleacetic acid and 24-epibrassinolide. We found a positive correlation among the expression levels of NtANTL, cyclin NtCYCD3;1 and cyclin-dependent kinase NtCDKB1-1 genes, suggesting possible molecular links between AINTEGUMENTA and cell cycle regulators in tobacco plants. However, no correlation was observed between NtANTL, NtCYCD3;1 and NtCDKB1-1 expression levels in response to NaCl and ABA. These observations indicate that the transcription factor NtANTL was not involved in the regulation of the cellular response to salinity nor did it affect the expression of NtCYCD3;1 and NtCDKB1-1 when tobacco plants were exposed to salt stress and ABA. In addition, we generated transgenic tobacco plants with both up-regulated and down-regulated expression of the NtANTL gene. Constitutive expression of the NtANTL gene contributed to an increase in the size of leaves and corolla of transgenic plants. Transgenic plants with reduced expression of the NtANTL gene had smaller leaves, flowers and stems, but showed a compensatory increase in the cell size of leaves and flowers. The results show the significance of the NtANTL gene for the control of organ growth by both cell division and expansion in tobacco plants.

Pistillody mutant reveals key insights into stamen and pistil development in wheat (Triticum aestivum L.)

BACKGROUND

The pistillody mutant wheat (Triticum aestivum L.) plant HTS-1 exhibits homeotic transformation of stamens into pistils or pistil-like structures. Unlike common wheat varieties, HTS-1 produces three to six pistils per floret, potentially increasing the yield. Thus, HTS-1 is highly valuable in the study of floral development in wheat. In this study, we conducted RNA sequencing of the transcriptomes of the pistillody stamen (PS) and the pistil (P) from HTS-1 plants, and the stamen (S) from the non-pistillody control variety Chinese Spring TP to gain insights into pistil and stamen development in wheat.

RESULTS

Approximately 40 Gb of processed reads were obtained from PS, P, and S. De novo assembly yielded 121,210 putative unigenes, with a mean length of 695 bp. Among these high-quality unigenes, 59,199 (48.84%) had at least one significant match with an existing gene model. A total of 23, 263, and 553 differentially expressed genes were identified in PS vs. P, PS vs. S, and P vs. S, respectively, with differences in expression greater than five-fold. Among the differentially expressed genes, 206 were highly correlated with stamen and pistil development. These genes include WM27B, DL, YAB1, YABBY4, WM 5, CER 1, and WBLH1, which have been implicated in flower development. The expression patterns of 25 differentially expressed genes were confirmed through quantitative real-time reverse transcription PCR.

CONCLUSIONS

Analysis of this transcriptome resource enabled us to characterize gene expression profiles, examine differential gene expression, and produce a candidate gene list related to wheat stamen and pistil development. This work is significant for the development of genomic resources for wheat, and provides important insights into the molecular mechanisms of wheat stamen and pistil development.

Mapping QTLs of yield-related traits using RIL population derived from common wheat and Tibetan semi-wild wheat

QTLs controlling yield-related traits were mapped using a population derived from common wheat and Tibetan semi-wild wheat and they provided valuable information for using Tibetan semi-wild wheat in future wheat molecular breeding. Tibetan semi-wild wheat (Triticum aestivum ssp tibetanum Shao) is a kind of primitive hexaploid wheat and harbors several beneficial traits, such as tolerance to biotic and abiotic stresses. And as a wild relative of common wheat, heterosis of yield of the progeny between them was significant. This study focused on mapping QTLs controlling yield-related traits using a recombined inbred lines (RILs) population derived from a hybrid between a common wheat line NongDa3331 (ND3331) and the Tibetan semi-wild wheat accession Zang 1817. In nine location-year environments, a total of 148 putative QTLs controlling nine traits were detected, distributed on 19 chromosomes except for 1A and 2D. Single QTL explained the phenotypic variation ranging from 3.12 to 49.95%. Of these QTLs, 56 were contributed by Zang 1817. Some stable QTLs contributed by Zang 1817 were also detected in more than four environments, such as QPh-3A1, QPh-4B1 and QPh-4D for plant height, QSl-7A1 for spike length, QEp-4B2 for ears per plant, QGws-4D for grain weight per spike, and QTgw-4D for thousand grain weight. Several QTL-rich Regions were also identified, especially on the homoeologous group 4. The TaANT gene involved in floral organ development was mapped on chromosome 4A between Xksm71 and Xcfd6 with 0.8 cM interval, and co-segregated with the QTLs controlling floret number per spikelet, explaining 4.96-11.84% of the phenotypic variation. The current study broadens our understanding of the genetic characterization of Tibetan semi-wild wheat, which will enlarge the genetic diversity of yield-related traits in modern wheat breeding program.

AINTEGUMENTA-LIKE proteins: hubs in a plethora of networks

Members of the AINTEGUMENTA-LIKE (AIL) family of APETALA 2/ETHYLENE RESPONSE FACTOR (AP2/ERF) domain transcription factors are expressed in all dividing tissues in the plant, where they have central roles in developmental processes such as embryogenesis, stem cell niche specification, meristem maintenance, organ positioning, and growth. When overexpressed, AIL proteins induce adventitious growth, including somatic embryogenesis and ectopic organ formation. The Arabidopsis (Arabidopsis thaliana) genome contains eight AIL genes, including AINTEGUMENTA, BABY BOOM, and the PLETHORA genes. Studies on these transcription factors have revealed their intricate relationship with auxin as well as their involvement in an increasing number of gene regulatory networks, in which extensive crosstalk and feedback loops have a major role.

Nucleotide diversity and molecular evolution of the WAG-2 gene in common wheat (Triticum aestivum L) and its relatives

In this work, we examined the genetic diversity and evolution of the WAG-2 gene based on new WAG-2 alleles isolated from wheat and its relatives. Only single nucleotide polymorphisms (SNP) and no insertions and deletions (indels) were found in exon sequences of WAG-2 from different species. More SNPs and indels occurred in introns than in exons. For exons, exons+introns and introns, the nucleotide polymorphism π decreased from diploid and tetraploid genotypes to hexaploid genotypes. This finding indicated that the diversity of WAG-2 in diploids was greater than in hexaploids because of the strong selection pressure on the latter. All dn/ds ratios were < 1.0, indicating that WAG-2 belongs to a conserved gene affected by negative selection. Thirty-nine of the 57 particular SNPs and eight of the 10 indels were detected in diploid species. The degree of divergence in intron length among WAG-2 clones and phylogenetic tree topology suggested the existence of three homoeologs in the A, B or D genome of common wheat. Wheat AG-like genes were divided into WAG-1 and WAG-2 clades. The latter clade contained WAG-2, OsMADS3 and ZMM2 genes, indicating functional homoeology among them.

Characterization of wheat Bell1-type homeobox genes in floral organs of alloplasmic lines with Aegilops crassa cytoplasm

BACKGROUND

Alloplasmic wheat lines with Aegilops crassa cytoplasm often show homeotic conversion of stamens into pistils under long-day conditions. In the pistillody-exhibiting florets, an ectopic ovule is formed within the transformed stamens, and female sterility is also observed because of abnormal integument development.

RESULTS

In this study, four wheat Bell1-like homeobox (BLH) genes were isolated and named WBLH1 to WBLH4. WBLH1/WBLH3/WBLH4 expression was observed in the basal boundary region of the ovary in both normal pistils and transformed stamens. WBLH2 was also strongly expressed in integuments not only of normal ovules in pistils but also of the ectopic ovules in transformed stamens, and the WBLH2 expression pattern in the sterile pistils seemed to be identical to that in normal ovules of fertile pistils. In addition, WBLH1 and WBLH3 showed interactions with the three wheat KNOX proteins through the BEL domain. WBLH2, however, formed a complex with wheat KNOTTED1 and ROUGH SHEATH1 orthologs through SKY and BEL domains, but not with a wheat LIGULELESS4 ortholog.

CONCLUSIONS

Expression of the four WBLH genes is evident in reproductive organs including pistils and transformed stamens and is independent from female sterility in alloplasmic wheat lines with Ae. crassa cytoplasm. KNOX-BLH interaction was conserved among various plant species, indicating the significance of KNOX-BLH complex formation in wheat developmental processes. The functional features of WBLH2 are likely to be distinct from other BLH gene functions in wheat development.

Class D and B(sister) MADS-box genes are associated with ectopic ovule formation in the pistil-like stamens of alloplasmic wheat (Triticum aestivum L.)

Homeotic transformation of stamens into pistil-like structures (pistillody) has been reported in cytoplasmic substitution (alloplasmic) lines of bread wheat (Triticum aestivum L.) that have the cytoplasm of a related wild species, Aegilops crassa. An ectopic ovule differentiates in the pistil-like stamen in the alloplasmic wheat. The SEEDSTICK (STK)-like class D MADS-box gene, wheat STK (WSTK), was expressed in the primordia of ectopic ovules in the pistil-like stamens as well as in the true pistil, suggesting that ectopic ovule formation results from WSTK expression in the pistil-like stamens of alloplasmic wheat. The ectopic ovule is abnormal as it fails to form complete integuments. Based on the expression pattern of WSTK and B(sister) MADS-box gene, WBsis (wheat B ( sister )), we conclude that WSTK plays a role in determination of ovule identity in the pistil-like stamen, but complete ovule development fails due to aberrant expression of WBsis.