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Abstract Background Cotton fiber is a model tissue for studying microtubule-associated proteins (MAPs). The Xklp2 (TPX2) proteins that belong to the novel MAPs member mainly participate in the formation and development of microtubule (MT). However, there is a lack of studies concerning the systematic characterization of the TPX2 genes family in cotton. Therefore, the identification and portrayal of G. hirsutum TPX2 genes can provide key targets for molecular manipulation in the breeding of cotton fiber improvement. Result In this study, TPX2 family genes were classified into two distinct subclasses TPXLs and MAP genes WAVE DAMPENED2-LIKE (WDLs) and quite conservative in quantity. GhWDL3 was significantly up-regulated in 15 days post anthesis fibers of ZRI-015 (an upland cotton with longer and stronger fiber). GhWDL3 promotes all stem hairs to become straight when overexpressed in Arabidopsis, which may indirectly regulate cotton fiber cell morphology during fiber development. Virus induced gene silencing (VIGS) results showed that GhWDL3 inhibited fiber cell elongation at fiber development periods through regulating the expression of cell wall related genes. Conclusion These results reveal that GhWDL3 regulated cotton fiber cell elongation and provide crucial information for the further investigation in the regulatory mechanisms/networks of cotton fiber length.

Abstract Background Gossypium hirsutum undergoes rapid clonal propagation to regenerate a mature plant through tissue culture. However, the correlation between cotton leaf regeneration, callus induction, and regeneration ability was still obscure. In this research, cotton leaf regeneration level for 21 accessions in the field (new leaves) was observed after the first harvest, and a comparison between field regeneration level and callus induction with its regeneration capacity (new shoots and roots) for the same 21 accessions was carried out. Agronomic traits, including plant height, leaf area, fresh leaf weight, dry leaf weight, the number of flowers and bolls, and biochemical (proline content) and physiological (chlorophyll and carotenoid content) traits during the flowering stage of 21 upland cotton accessions, were investigated. Result A significant correlation between physiological parameters and callus induction was discovered. Callus induction and regeneration capacity of roots and shoots for hypocotyl, cotyledons, and shoot tip tissues were used to validate field leaf regeneration level after the first harvest. CCRI 24 showed significant leaf regeneration in the field and callus induction capacity through callus induction and regeneration. Conclusion We found a substantial relationship between field regeneration capability and callus induction with its regeneration capacity for the hypocotyl, cotyledons, and shoot tip. The results showed that ZS061, Lumian 378, Jimian 863, and ZS065 have the highest moisture retention capacity, while CCRI 24, Liaoyang Duomaomian, and Beizhe Gongshemian have the lowest moisture retention capacity. CCRI 24 has the highest leaf regeneration capacity in the field, while Beizhe Gongshemian has the lowest leaf regeneration capacity. All our result provides a clue for checking the regeneration capacity through leaf regeneration level in the field.

Abstract Background The lateral root is one of the most important organs that constitute the root architecture system in plants. It can directly affect the contact area between plants and soil and plays an important role in plant structural support and nutrient absorption. Optimizing root architecture systems can greatly increase crop yields. This study was designed to identify the molecular markers and candidate genes associated with lateral root development in cotton and to evaluate correlations with yield and disease traits. Result The number of lateral roots for 14-day old seedlings was recorded for 215 Gossypium arboreum accessions. A correlation analysis showed that the number of lateral roots positively correlates with the sympodial branch node and seed index traits, but negatively correlates with lint percentage. A Genome-wide association study (GWAS) identified 18 significant SNPs with 19 candidate genes associated with the lateral root number. Expression analysis identified three genes (FLA12, WRKY29, and RBOHA) associated with lateral root development. Conclusion GWAS analysis identified key SNPs and candidate genes for lateral root number, and genes of FLA12, WRKY29, and RBOHA may play a pivotal role in lateral root development in Asian cotton.

Abstract Background Cotton fibers are single-celled extensions of the seed epidermis, a model tissue for studying cytoskeleton. Tubulin genes play a critical role in synthesizing the microtubules (MT) as a core element of the cytoskeleton. However, there is a lack of studies concerning the systematic characterization of the tubulin gene family in cotton. Therefore, the identification and portrayal of G. hirsutum tubulin genes can provide key targets for molecular manipulation in cotton breeding. Result In this study, we investigated all tubulin genes from different plant species and identified 98 tubulin genes in G. hirsutum. Phylogenetic analysis showed that tubulin family genes were classified into three subfamilies. The protein motifs and gene structure of α-, β-tubulin genes are more conserved compared with γ-tubulin genes. Most tubulin genes are located at the proximate ends of the chromosomes. Spatiotemporal expression pattern by transcriptome and qRT-PCR analysis revealed that 12 α-tubulin and 7 β-tubulin genes are specifically expressed during different fiber development stages. However, Gh.A03G027200, Gh.D03G169300, and Gh.A11G258900 had differential expression patterns at distinct stages of fiber development in varieties J02508 and ZRI015. Conclusion In this study, the evolutionary analysis showed that the tubulin genes were divided into three clades. The genetic structures and molecular functions were highly conserved in different plants. Three candidate genes, Gh.A03G027200, Gh.D03G169300, and Gh.A11G258900 may play a key role during fiber development complementing fiber length and strength.

Abstract Background Stem hardness is one of the major influencing factors for plant architecture in upland cotton (Gossypium hirsutum L.). Evaluating hardness phenotypic traits is very important for the selection of elite lines for resistance to lodging in Gossypium hirsutum L. Cotton breeders are interested in using diverse genotypes to enhance fiber quality and high-yield. Few pieces of research for hardness and its relationship with fiber quality and yield were found. This study was designed to find the relationship of stem hardness traits with fiber quality and yield contributing traits of upland cotton. Results Experiments were carried out to measure the bending, acupuncture, and compression properties of the stem from a collection of upland cotton genotypes, comprising 237 accessions. The results showed that the genotypic difference in stem hardness was highly significant among the genotypes, and the stem hardness traits (BL, BU, AL, AU, CL, and CU) have a positive association with fiber quality traits and yield-related traits. Statistical analyses of the results showed that in descriptive statistics result bending (BL, BU) has a maximum coefficient of variance, but fiber length and fiber strength have less coefficient of variance among the genotypes. Principal component analysis (PCA) trimmed quantitative characters into nine principal components. The first nine principal components (PC) with Eigenvalues > 1 explained 86% of the variation among 237 accessions of cotton. Both 2017 and 2018, PCA results indicated that BL, BU, FL, FE, and LI contributed to their variability in PC1, and BU, AU, CU, FD, LP, and FWPB have shown their variability in PC2. Conclusion We describe here the systematic study of the mechanism involved in the regulation of enhancing fiber quality and yield by stem bending strength, acupuncture, and compression properties of G. hirsutum.

Abstract Background Upland cotton (Gossypium hirsutum) accounts for more than 90% of the annual world cotton output because of its high yield potential. However, yield and fiber quality traits often show negative correlations. We constructed four F2 populations of upland cotton, using two normal lines (4133B and SGK9708) with high yield potential but moderate fiber quality and two introgression lines (Suyuan04–3 and J02–247) with superior fiber quality, and used them to investigate the genetic basis underlying complex traits such as yield and fiber quality in upland cotton. We also phenotyped eight agronomic and economic traits and mapped quantitative trait loci (QTLs). Results Extensive phenotype variations and transgressive segregation were found across the segregation populations. We constructed four genetic maps of 585.97 centiMorgan (cM), 752.45 cM, 752.45 cM, and 1 163.66 cM, one for each of the four F2 populations. Fifty QTLs were identified across the four populations (7 for plant height, 27 for fiber quality and 16 for yield). The same QTLs were identified in different populations, including qBW4 and qBW2, which were linked to a common simple sequence repeat (SSR) marker, NAU1255. A QTL cluster containing eight QTLs for six different traits was characterized on linkage group 9 of the 4133B × Suyuan04–3 population. Conclusions These findings will provide insights into the genetic basis of simultaneous improvement of yield and fiber quality in upland cotton breeding.

Abstract Background Gossypium arboreum is a diploid species cultivated in the Old World. It possesses favorable characters that are valuable for developing superior cotton cultivars. Method A set of 197 Gossypium arboreum accessions were genotyped using 80 genome-wide SSR markers to establish patterns of the genetic diversity and population structure. These accessions were collected from three major G. arboreum growing areas in China. A total of 255 alleles across 80 markers were identified in the genetic diversity analysis. Results Three subgroups were found using the population structure analysis, corresponding to the Yangtze River Valley, North China, and Southwest China zones of G.arboreum growing areas in China. Average genetic distance and Polymorphic information content value of G. arboreum population were 0.34 and 0.47, respectively, indicating high genetic diversity in the G. arboreum germplasm pool. The Phylogenetic analysis results concurred with the subgroups identified by Structure analysis with a few exceptions. Variations among and within three groups were observed to be 13.61% and 86.39%, respectively. Conclusion The information regarding genetic diversity and population structure from this study is useful for genetic and genomic analysis and systematic utilization of economically important traits in G. arboreum.