Molecular Evolution and Stress and Phytohormone Responsiveness of SUT Genes in Gossypium hirsutum

The high-affinity pineapple sucrose transporter AcSUT1B, regulated by AcCBF1, exhibited enhanced cold tolerance in transgenic Arabidopsis

Sucrose transporter (SUT) plays essential roles in plant growth and development, as well as responses to diverse abiotic stresses. However, limited information about the function of SUT was available in pineapple, an important tropical fruit crop with crassulacean acid metabolism. Here, four AcSUT genes were identified in pineapple genome, and divided into three clades according to the phylogenetic analysis. The expression profiles of AcSUTs were systemically examined, and they were all localized to plasma membrane. Transport activity assay by two-electrode voltage clamp of Xenopus oocytes showed that AcSUT1A and AcSUT1B were capable of transporting a range of glucosides, and they were exhibited high affinity for sucrose with Km value of 0.09 mM and 0.41 mM at pH 5.0, respectively. Overexpression of the cold-induced AcSUT1B conferred enhanced cold tolerance in transgenic Arabidopsis. DNA-protein interaction analysis further demonstrated that AcCBF1 directly binds the CRT/DRE element of the AcSUT1B promoter and activated its expression. Heterologous expression of AcCBF1 in Arabidopsis also increased cold tolerance. In this study, we investigated the transport activities of AcSUTs in pineapple and identified the AcCBF1-AcSUT1B module involved in cold stress, which provided new insights into the molecular mechanism of the cold response in pineapple.

Identification and molecular evolution of the GLX genes in 21 plant species: a focus on the Gossypium hirsutum

BACKGROUND

The glyoxalase system includes glyoxalase I (GLXI), glyoxalase II (GLXII) and glyoxalase III (GLXIII), which are responsible for methylglyoxal (MG) detoxification and involved in abiotic stress responses such as drought, salinity and heavy metal.

RESULTS

In this study, a total of 620 GLX family genes were identified from 21 different plant species. The results of evolutionary analysis showed that GLX genes exist in all species from lower plants to higher plants, inferring that GLX genes might be important for plants, and GLXI and GLXII account for the majority. In addition, motif showed an expanding trend in the process of evolution. The analysis of cis-acting elements in 21 different plant species showed that the promoter region of the GLX genes were rich in phytohormones and biotic and abiotic stress-related elements, indicating that GLX genes can participate in a variety of life processes. In cotton, GLXs could be divided into two groups and most GLXIs distributed in group I, GLXIIs and GLXIIIs mainly belonged to group II, indicating that there are more similarities between GLXII and GLXIII in cotton evolution. The transcriptome data analysis and quantitative real-time PCR analysis (qRT-PCR) show that some members of GLX family would respond to high temperature treatment in G.hirsutum. The protein interaction network of GLXs in G.hirsutum implied that most members can participate in various life processes through protein interactions.

CONCLUSIONS

The results elucidated the evolutionary history of GLX family genes in plants and lay the foundation for their functions analysis in cotton.

Genome-wide identification and expression analysis of SUT gene family members in sugar beet (Beta vulgaris L.)

Sucrose transporters (SUTs) play an important role in the transmembrane transport and distribution of sucrose, and their activity has an important impact on plant growth and crop yield. In this study, the SUT gene family was identified in the whole beet genome using bioinformatics methods, and gene characteristics, subcellular localization prediction, phylogenetic evolution, promoter cis-elements and expression patterns were systematically analyzed. A total of 9 SUT gene family members were identified from in beet genome and divided into 3 different groups (group 1, group 2, and Group 3), which were unevenly distributed on 4 chromosomes. Most SUT family members contained photoresponsive and hormone-regulated response elements. Subcellular localization prediction showed that the BvSUT genes are all located in the inner membrane, and most of the terms identified through GO enrichment analysis are classified as "membrane" related. The results of RT-qPCR showed that the expression level of the BvSUT gene was significantly higher in the tuber enlargement stage (100-140 d) than in other stages. This study is the first to analyze the BvSUT gene family in sugar beet, and it provides a theoretical basis for the functional exploration and application of SUT genes in crop improvement, especially in sugar crops.

Evolutionary History and Functional Diversification of the JmjC Domain-Containing Histone Demethylase Gene Family in Plants

Histone demethylases containing JumonjiC (JmjC) domains regulate gene transcription and chromatin structure by changing the methylation status of lysine residues and play an important role in plant growth and development. In this study, a total of 332 JmjC family genes were identified from 21 different plant species. The evolutionary analysis results showed that the JmjC gene was detected in each species, that is, the gene has already appeared in algae. The phylogenetic analysis showed that the KDM3/JHDM2 subfamily genes may have appeared when plants transitioned from water to land, but were lost in lycophytes (Selaginella moellendorffii). During the evolutionary process, some subfamily genes may have been lost in individual species. According to the analysis of the conserved domains, all of the plant JmjC genes contained a typical JmjC domain, which was highly conserved during plant evolution. The analysis of cis-acting elements showed that the promoter region of the JmjC gene was rich in phytohormones and biotic and abiotic stress-related elements. The transcriptome data analysis and protein interaction analyses showed that JmjC genes play an important role in plant growth and development. The results clarified the evolutionary history of JmjC family genes in plants and lay the foundation for the analysis of the biological functions of JmjC family genes.

Plasma membrane-localized SEM1 protein mediates sugar movement to sink rice tissues

The translocation of photosynthate carbohydrates, such as sucrose, is critical for plant growth and crop yield. Previous studies have revealed that sugar transporters, plasmodesmata and sieve plates act as important controllers in sucrose loading into and unloading from phloem in the vascular system. However, other pivotal steps for the regulation of sucrose movement remain largely elusive. In this study, characterization of two starch excesses in mesophyll (sem) mutants and dye and sucrose export assays were performed to provide insights into the regulatory networks that drive source-sink relations in rice. Map-based cloning identified two allelic mutations in a gene encoding a GLUCAN SYNTHASE-LIKE (GSL) protein, thus indicating a role for SEM1 in callose biosynthesis. Subcellular localization in rice showed that SEM1 localized to the plasma membrane. In situ expression analysis and GUS staining showed that SEM1 was mainly expressed in vascular phloem cells. Reduced sucrose transport was found in the sem1-1/1-2 mutant, which led to excessive starch accumulation in source leaves and inhibited photosynthesis. Paraffin section and transmission electron microscopy experiments revealed that less-developed vascular cells (VCs) in sem1-1/1-2 potentially disturbed sugar movement. Moreover, dye and sugar trafficking experiments revealed that aberrant VC development was the main reason for the pleiotropic phenotype of sem1-1/1-2. In total, efficient sucrose loading into the phloem benefits from an optional number of VCs with a large vacuole that could act as a buffer holding tank for sucrose passing from the vascular bundle sheath.

Phylogenetic relationships of sucrose transporters (SUTs) in plants and genome-wide characterization of SUT genes in Orchidaceae reveal roles in floral organ development

Sucrose is the primary form of photosynthetically produced carbohydrates transported long distance in many plant species and substantially affects plant growth, development and physiology. Sucrose transporters (SUTs or SUCs) are a group of membrane proteins that play vital roles in mediating sucrose allocation within cells and at the whole-plant level. In this study, we investigated the relationships among SUTs in 24 representative plant species and performed an analysis of SUT genes in three sequenced Orchidaceae species: Dendrobium officinale, Phalaenopsis equestris, and Apostasia shenzhenica. All the SUTs from the 24 plant species were classified into three groups and five subgroups, subgroups A, B1, B2.1, B2.2, and C, based on their evolutionary relationships. A total of 22 SUT genes were identified among Orchidaceae species, among which D. officinale had 8 genes (DoSUT01-08), P. equestris had eight genes (PeqSUT01-08) and A. shenzhenica had 6 genes (AsSUT01-06). For the 22 OrchidaceaeSUTs, subgroups A, B2.2 and C contained three genes, whereas the SUT genes were found to have significantly expanded in the monocot-specific subgroup B2.1, which contained 12 genes. To understand sucrose partitioning and the functions of sucrose transporters in Orchidaceae species, we analyzed the water-soluble sugar content and performed RNA sequencing of different tissues of D. officinale, including leaves, stems, flowers and roots. The results showed that although the total content of water-soluble polysaccharides was highest in the stems of D. officinale, the sucrose content was highest in the flowers. Moreover, gene expression analysis showed that most of the DoSUTs were expressed in the flowers, among which DoSUT01,DoSUT07 and DoSUT06 had significantly increased expression levels. These results indicated that stems are used as the main storage sinks for photosynthetically produced sugar in D. officinale and that DoSUTs mainly function in the cellular machinery and development of floral organs. Our findings provide valuable information on sucrose partitioning and the evolution and functions of SUT genes in Orchidaceae and other species.

Characterization and Stress Response of the JmjC Domain-Containing Histone Demethylase Gene Family in the Allotetraploid Cotton Species Gossypium hirsutum

Histone modification is an important epigenetic modification that controls gene transcriptional regulation in eukaryotes. Histone methylation is accomplished by histone methyltransferase and can occur on two amino acid residues, arginine and lysine. JumonjiC (JmjC) domain-containing histone demethylase regulates gene transcription and chromatin structure by changing the methylation state of the lysine residue site and plays an important role in plant growth and development. In this study, we carried out genome-wide identification and comprehensive analysis of JmjC genes in the allotetraploid cotton species Gossypium hirsutum. In total, 50 JmjC genes were identified and in G. hirsutum, and 25 JmjC genes were identified in its two diploid progenitors, G. arboreum and G. raimondii, respectively. Phylogenetic analysis divided these JmjC genes into five subfamilies. A collinearity analysis of the two subgenomes of G. hirsutum and the genomes of G. arboreum and G. raimondii uncovered a one-to-one relationship between homologous genes of the JmjC gene family. Most homologs in the JmjC gene family between A and D subgenomes of G. hirsutum have similar exon-intron structures, which indicated that JmjC family genes were conserved after the polyploidization. All G. hirsutumJmjC genes were found to have a typical JmjC domain, and some genes also possess other special domains important for their function. Analysis of promoter regions revealed that cis-acting elements, such as those related to hormone and abiotic stress response, were enriched in G. hirsutum JmjC genes. According to a reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis, most G. hirsutumJmjC genes had high abundance expression at developmental stages of fibers, suggesting that they might participate in cotton fiber development. In addition, some G. hirsutumJmjC genes were found to have different degrees of response to cold or osmotic stress, thus indicating their potential role in these types of abiotic stress response. Our results provide useful information for understanding the evolutionary history and biological function of JmjC genes in cotton.

Transcriptional characterization and response to defense elicitors of mevalonate pathway genes in cotton (Gossypium arboreum L.)

The mevalonate (MVA) pathway is responsible for the biosynthesis of cytosolic terpenes including gossypol and its derivatives, which play an important role in the cotton plant’s defense against pathogens and herbivores. In this study, we identified and cloned 17 potentially functional genes encoding enzymes that catalyze the six steps of the MVA pathway in Gossypium arboreum. Expression pattern analysis by qRT-PCR demonstrated that these genes had tissue-specific expression profiles and were most prevalently expressed in roots. Moreover, these genes were up-regulated in response to several elicitors, including methyl jasmonate and salicylic acid, as well as Verticillium dahliae infection and Helicoverpa armigera infestation. This indicates that the MVA pathway genes are involved in the signaling pathway regulated by exogenous hormones and the resistance of cotton plants to pathogens and herbivores. Our results improve the understanding of cytosolic terpene biosynthesis in Gossypium species and lay the foundation for further research on gossypol biosynthesis.