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Disease resistance (R) genes have been isolated from many plant species and R genes with domains of nucleotide binding sites (NBS) and leucine-rich repeats (LRR) represent the largest R gene family. The objective of this investigation was to test a resistance gene analog (RGA) anchored marker system, called amplified fragment length polymorphism (AFLP)-RGA in cotton (Gossypium spp.). The AFLP-RGA analysis uses one degenerate RGA primer designed from various NBS and LRR domains of R genes in combination with one selective AFLP primer in a PCR reaction. Out of a total of 446 AFLP-RGA bands amplified by 22 AFLP-RGA primer combinations, 76 (17.0%) and 37 (8.3%) were polymorphic within four G. hirsutum L. genotypes and four G. barbadense L. cotton genotypes, respectively. The number of polymorphic AFLP-RGA bands (256) between G. hirsutum and G. barbadense was much higher (57.4%). This level of polymurphism mirrors that of AFLP. The genetic similarity among the eight genotypes based on AFLP-RGA or AFLP lead to similar results in genotype grouping at the species and intraspecies level. However, RGA markers amplified by only degenerate RGA primers could not discriminate several genotypes. AFLP-RGA offers a great flexibility for numerous primer combinations in a genome-wide search for RGAs. Due to the distribution of RGAs or RGA clusters in the plant genome, genome-wide AFLP-RGA analysis provides a useful resource for candidate gene mapping of R genes for disease resistance in cotton.

Glycerol-3-phosphate acyltransferases (GPATs), critical for multiple biological processes like male fertility, have been extensively characterized. However, their precise functions and underlying regulatory mechanism in cotton anther development are unclear. This research demonstrated the importance of GhGPAT12 / 25 (a paralogs pair on A12/D12 sub-chromosome of cotton) to regulate the degradation of tapetum, anther cuticle formation, and pollen exine development. GhGPAT12 and GhGPAT25 exhibited specifically detected transcripts in tapetum and pollen exine during the early anther developmental stages. GhGPAT12/25 are sn-2 glycerol-3-phosphate acyltransferases and can transfer the acyl group of palmitoyl-CoA to glycerol-3-phosphate (G3P). CRISPR/Cas9-mediated knockout identified the functional redundancy of GhGPAT12 and GhGPAT25. Knockout of both genes caused completely male sterility associated with abnormal anther cuticle, swollen tapetum, and inviable microspores with defective exine and irregular unrestricted shape. RNA-seq analysis showed that the loss of function of GhGPAT12 / 25 affects the processes of wax metabolic, glycerol monomer biosynthesis, and transport. Consistently, cuticular waxes were dramatically reduced in mutant anthers. Yeast one-hybrid system (Y1H), virus-induced gene silencing (VIGS), and dual-luciferase (LUC) assays illustrated that GhMYB80s are likely to directly activate the expression of GhGPAT12 / 25. This study provides important insights for revealing the regulatory mechanism underlying anther development in cotton. [ABSTRACT FROM AUTHOR]

Abstract Background Upland cotton (G. hirsutum L.) is the leading fiber crop worldwide. Genetic improvement of fiber quality and yield is facilitated by a variety of genomics tools. An integrated genetic and physical map is needed to better characterize quantitative trait loci and to allow for the positional cloning of valuable genes. However, developing integrated genomic tools for complex allotetraploid genomes, like that of cotton, is highly experimental. In this report, we describe an effective approach for developing an integrated physical framework that allows for the distinguishing between subgenomes in cotton. Results A physical map has been developed with 220 and 115 BAC contigs for homeologous chromosomes 12 and 26, respectively, covering 73.49 Mb and 34.23 Mb in physical length. Approximately one half of the 220 contigs were anchored to the At subgenome only, while 48 of the 115 contigs were allocated to the Dt subgenome only. Between the two chromosomes, 67 contigs were shared with an estimated overall physical similarity between the two chromosomal homeologs at 40.0 %. A total of 401 fiber unigenes plus 214 non-fiber unigenes were located to chromosome 12 while 207 fiber unigenes plus 183 non-fiber unigenes were allocated to chromosome 26. Anchoring was done through an overgo hybridization approach and all anchored ESTs were functionally annotated via blast analysis. Conclusion This integrated genomic map describes the first pair of homoeologous chromosomes of an allotetraploid genome in which BAC contigs were identified and partially separated through the use of chromosome-specific probes and locus-specific genetic markers. The approach used in this study should prove useful in the construction of genome-wide physical maps for polyploid plant genomes including Upland cotton. The identification of Gene-rich islands in the integrated map provides a platform for positional cloning of important genes and the targeted sequencing of specific genomic regions.

Summary: The transition from vegetative to reproductive growth is very important for early maturity in cotton. However, the genetic control of this highly dynamic and complex developmental process remains unclear. A high‐resolution tissue‐ and stage‐specific transcriptome profile was generated from six developmental stages using 72 samples of two early‐maturing and two late‐maturing cotton varieties. The results of histological analysis of paraffin sections showed that flower bud differentiation occurred at the third true leaf stage (3TLS) in early‐maturing varieties, but at the fifth true leaf stage (5TLS) in late‐maturing varieties. Using pairwise comparison and weighted gene co‐expression network analysis, 5312 differentially expressed genes were obtained, which were divided into 10 gene co‐expression modules. In the MElightcyan module, 46 candidate genes regulating cotton flower bud differentiation were identified and expressed at the flower bud differentiation stage. A novel key regulatory gene related to flower bud differentiation, GhCAL, was identified in the MElightcyan module. Anti‐GhCAL transgenic cotton plants exhibited late flower bud differentiation and flowering time. GhCAL formed heterodimers with GhAP1‐A04/GhAGL6‐D09 and regulated the expression of GhAP1‐A04 and GhAGL6‐D09. GhAP1‐A04‐ and GhAGL6‐D09‐silenced plants also showed significant late flowering. Finally, we propose a new flowering regulatory pathway mediated by GhCAL. This study elucidated the molecular mechanism of cotton flowering regulation and provides good genetic resources for cotton early‐maturing breeding. [ABSTRACT FROM AUTHOR]

Summary: Although upland cotton (Gossypium hirsutism L.) originated in the tropics, this early maturity cotton can be planted as far north as 46°N in China due to the accumulation of numerous phenotypic and physiological adaptations during domestication. However, how the genome of early maturity cotton has been altered by strong human selection remains largely unknown. Herein, we report a cotton genome variation map generated by the resequencing of 436 cotton accessions. Whole‐genome scans for sweep regions identified 357 putative selection sweeps covering 4.94% (112 Mb) of the upland cotton genome, including 5184 genes. These genes were functionally related to flowering time control, hormone catabolism, ageing and defence response adaptations to environmental changes. A genome‐wide association study (GWAS) for seven early maturity traits identified 307 significant loci, 22.48% (69) of which overlapped with putative selection sweeps that occurred during the artificial selection of early maturity cotton. Several previously undescribed candidate genes associated with early maturity were identified by GWAS. This study provides insights into the genetic basis of early maturity in upland cotton as well as breeding resources for cotton improvement. [ABSTRACT FROM AUTHOR]