Genome-Wide Analysis of AAT Genes and Their Expression Profiling during Fiber Development in Cotton

Amino acid transporters (AATs) are a kind of membrane proteins that mediate the transport of amino acids across cell membranes in higher plants. The AAT proteins are involved in regulating plant cell growth and various developmental processes. However, the biological function of this gene family in cotton fiber development is not clear. In this study, 190, 190, 101, and 94 full-length AAT genes were identified from Gossypiumhirsutum, G. barbadense, G. arboreum, and G. raimondii. A total of 575 AAT genes from the four cotton species were divided into two subfamilies and 12 clades based on phylogenetic analysis. The AAT genes in the four cotton species were distributed on all the chromosomes. All GhAAT genes contain multiple exons, and each GhAAT protein has multiple conserved motifs. Transcriptional profiling and RT qPCR analysis showed that four GhATT genes tend to express specifically at the fiber initiation stage. Eight genes tend to express specifically at the fiber elongation and maturity stage, and four genes tend to express specifically at the fiber initiation and elongation stages. Our results provide a solid basis for further elucidating the biological function of AAT genes related to cotton fiber development and offer valuable genetic resources for crop improvement in the future.

Evolution of pectin synthesis relevant galacturonosyltransferase gene family and its expression during cotton fiber development

Background Pectin is a key substance involved in cell wall development, and the galacturonosyltransferases (GAUTs) gene family is a critical participant in the pectin synthesis pathway. Systematic and comprehensive research on GAUTs has not been performed in cotton. Analysis of the evolution and expression patterns of the GAUT gene family in different cotton species is needed to increase knowledge of the function of pectin in cotton fiber development. Results In this study, we have identified 131 GAUT genes in the genomes of four Gossypium species (G. raimondii, G. barbadense, G. hirsutum, and G. arboreum), and classified them as GAUT-A, GAUT-B and GAUT-C, which coding probable galacturonosyltransferases. Among them, the GAUT genes encode proteins GAUT1 to GAUT15. All GAUT proteins except for GAUT7 contain a conserved glycosyl transferase family 8 domain (H-DN-A-SVV-S-V-H-T-F). The conserved sequence of GAUT7 is PLN (phospholamban) 02769 domain. According to cis-elemet analysis, GAUT genes transcript levels may be regulated by hormones such as JA, GA, SA, ABA, Me-JA, and IAA. The evolution and transcription patterns of the GAUT gene family in different cotton species and the transcript levels in upland cotton lines with different fiber strength were analyzed. Peak transcript level of GhGAUT genes have been observed before 15 DPA. In the six materials with high fiber strength, the transcription of GhGAUT genes were concentrated from 10 to 15 DPA; while the highest transcript levels in low fiber strength materials were detected between 5 and 10 DPA. These results lays the foundation for future research on gene function during cotton fiber development. Conclusions The GAUT gene family may affect cotton fiber development, including fiber elongation and fiber thickening. In the low strength fiber lines, GAUTs mainly participate in fiber elongation, whereas their major effect on cotton with high strength fiber is related to both elongation and thickening.

Advances about the Roles of Membranes in Cotton Fiber Development

Cotton fiber is an extremely elongated single cell derived from the ovule epidermis and is an ideal model for studying cell development. The plasma membrane is tremendously expanded and accompanied by the coordination of various physiological and biochemical activities on the membrane, one of the three major systems of a eukaryotic cell. This review compiles the recent progress and advances for the roles of the membrane in cotton fiber development: the functions of membrane lipids, especially the fatty acids, sphingolipids, and phytosterols; membrane channels, including aquaporins, the ATP-binding cassette (ABC) transporters, vacuolar invertase, and plasmodesmata; and the regulation mechanism of membrane proteins, such as membrane binding enzymes, annexins, and receptor-like kinases.

Characterization of cotton ARF factors and the role of GhARF2b in fiber development

BackgroundCotton fiber is a model system for studying plant cell development. At present, the functions of many transcription factors in cotton fiber development have been elucidated, however, the roles of auxin response factor (ARF) genes in cotton fiber development need be further explored.ResultsHere, we identify auxin response factor (ARF) genes in three cotton species: the tetraploid upland cottonG. hirsutum, which has 73 ARF genes, and its putative extent parental diploidsG. arboreumandG. raimondii, which have 36 and 35 ARFs, respectively. Ka and Ks analyses revealed that inG. hirsutum ARFgenes have undergone asymmetric evolution in the two subgenomes. The cotton ARFs can be classified into four phylogenetic clades and are actively expressed in young tissues. We demonstrate thatGhARF2b, a homolog of the ArabidopsisAtARF2, was preferentially expressed in developing ovules and fibers. Overexpression ofGhARF2bby a fiber specific promoter inhibited fiber cell elongation but promoted initiation and, conversely, its downregulation by RNAi resulted in fewer but longer fiber. We show that GhARF2b directly interacts with GhHOX3 and represses the transcriptional activity of GhHOX3 on target genes.ConclusionOur results uncover an important role of the ARF factor in modulating cotton fiber development at the early stage.

Unravelling cotton RNAseq repositories to the fiber development specific modules and their alliance with the fiber-related traits

SummaryCotton fiber development is still an intriguing question to understand the fiber commitment and development. Here, we remapped >350 publicly available cotton RNA sequencing data on recently published cotton genome with ∼400 fold coverage. The differentially expressed genes were clustered in six modules whose functions are specific to commitment, initiation, elongation and Secondary Cell Wall (SCW) fiber development stages. Gene Ontology analysis of commitment and initiation specific modules suggests enrichment of genes involved in organ development. The modules specific for elongation and SCW showed significant enrichment of hydroxyproline-rich proteins and hydrolases. Transcription factors (TFs) binding frequency of defined modules suggested that homeodomain, MYB and NAC expresses at commitment stages but their expression was governed by other TFs. We also mined the stage-specific transcriptional biomarker and Exclusively Expressed Transcripts (EETs) for fiber. These EETs were positively selected during fiber evolution and cotton domestication. The extensive expression profiling of six EETs in 100 cotton genotypes at different fiber developmental stages using nCounter assay and their correlation with eight fiber-related suggests that several EETs are correlated with different fiber quality-related traits. Thus, our study reveals several important genes and pathways that may be important for cotton fiber development and future improvement of cotton.

Evolution of pectin-synthesis-relevant galacturonosyltransferase gene family and its expression during cotton fiber development

Background: Pectin is a key substance involved in cell wall development, and the galacturonosyltransferases (GAUTs) gene family is a critical participant in the pectin synthesis pathway. Systematic and comprehensive research on GAUTs has not been performed in cotton. Analysis of the evolution and expression patterns of the GAUT gene family in different cotton species is needed to increase knowledge of the function of pectin in cotton fiber development.Results: In this study, we identified 131 GAUT genes in the genomes of four Gossypium species (G. raimondii, G. barbadense, G. hirsutum, and G. arboreum), and classified them as GAUT-A, GAUT-B and GAUT-C. Among them, 15 GAUT genes encoded proteins (GAUT1 to GAUT15). All GAUT family genes except for the gene GAUT7 coding contained a consevrved Glyco_transf_8 domain (H-DN-A-SVV-S-V-H-T-F). The consevrved sequences of GAUT7 was a PLN (phospholamban) 02769 domain, categorized as a probable galacturonosyltransferase. According to cis-elemet analysis, GAUT genes expression may be regulated by hormones such as JA, GA, SA, ABA, Me-JA and IAA. The evolution and expression patterns of the GAUT gene family in different cotton species and the expression levels in upland cotton materials having different fiber strengths were analyzed. Peak expression of GhGAUT genes was observed before 15DPA; in the six materials with high fiber strength, the expression was concentrated from 10 to 15DPA; while the highest expression in low fiber strength materials was detected between 5 and 10 DPA. The results presented in this paper lays the foundation for future research on gene function during cotton fiber development.Conclusions: The GAUT gene family may affect cotton fiber development, including fiber elongation and fiber thickening. In the low-strength-fiber lines, GAUTs mainly participate in fiber elongation, whereas their major effect on cotton with high-strength fiber is related to both elongation and thickening.

Characterization of Cotton ARF Factors and the Role of GhARF2b in Fiber Development

Background: Cotton fiber is a model system for studying plant cell development. At present, our understanding of cotton fiber development and the regulatory network is still primitive. Results: Here, we identify auxin response factor (ARF) genes in three cotton species: the tetraploid upland cotton G. hirsutum, which has 73 ARF genes, and its putative extent parental diploids G. arboreum and G. raimondii, which have 36 and 35 ARFs, respectively. Ka and Ks analyses revealed that in G. hirsutum ARF genes have undergone asymmetric evolution in the two subgenomes. The cotton ARFs can be classified into four phylogenetic clades and are actively expressed in young tissues. We demonstrate that GhARF2b, a homolog of the Arabidopsis AtARF2, was preferentially expressed in developing ovules and fibers. Overexpression of GhARF2b by a fiber specific promoter inhibited fiber cell elongation but promoted initiation and, conversely, its downregulation by RNAi of resulted in fewer but longer fiber. Conclusion: Our results uncover an important role of the ARF factor in modulating cotton fiber development at the early stage.

Cotton Fiber Development Requires the Pentatricopeptide Repeat Protein GhIm for Splicing of Mitochondrial nad7 mRNA

Pentatricopeptide repeat (PPR) proteins encoded by nuclear genomes can bind to organellar RNA and are involved in the regulation of RNA metabolism. However, the functions of many PPR proteins remain unknown in plants, especially in polyploidy crops. Here, through a map-based cloning strategy and Clustered regularly interspaced short palindromic repeats/cas9 (CRISPR/cas9) gene editing technology, we cloned and verified an allotetraploid cotton immature fiber (im) mutant gene (GhImA) encoding a PPR protein in chromosome A03, that is associated with the non-fluffy fiber phenotype. GhImA protein targeted mitochondrion and could bind to mitochondrial nad7 mRNA, which encodes the NAD7 subunit of Complex I. GhImA and its homolog GhImD had the same function and were dosage-dependent. GhImA in the im mutant was a null allele with a 22 bp deletion in the coding region. Null GhImA resulted in the insufficient GhIm dosage, affected mitochondrial nad7 pre-mRNA splicing, produced less mature nad7 transcripts, and eventually reduced Complex I activities, up-regulated alternative oxidase metabolism, caused reactive oxygen species (ROS) burst and activation of stress or hormone response processes. This study indicates that the GhIm protein participates in mitochondrial nad7 splicing, affects respiratory metabolism, and further regulates cotton fiber development via ATP supply and ROS balance.