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Summary: The diploid wild cotton species Gossypium australe possesses excellent traits including resistance to disease and delayed gland morphogenesis, and has been successfully used for distant breeding programmes to incorporate disease resistance traits into domesticated cotton. Here, we sequenced the G. australe genome by integrating PacBio, Illumina short read, BioNano (DLS) and Hi‐C technologies, and acquired a high‐quality reference genome with a contig N50 of 1.83 Mb and a scaffold N50 of 143.60 Mb. We found that 73.5% of the G. australe genome is composed of various repeat sequences, differing from those of G. arboreum (85.39%), G. hirsutum (69.86%) and G. barbadense (69.83%). The G. australe genome showed closer collinear relationships with the genome of G. arboreum than G. raimondii and has undergone less extensive genome reorganization than the G. arboreum genome. Selection signature and transcriptomics analyses implicated multiple genes in disease resistance responses, including GauCCD7 and GauCBP1, and experiments revealed induction of both genes by Verticillium dahliae and by the plant hormones strigolactone (GR24), salicylic acid (SA) and methyl jasmonate (MeJA). Experiments using a Verticillium‐resistant domesticated G. barbadense cultivar confirmed that knockdown of the homologues of these genes caused a significant reduction in resistance against Verticillium dahliae. Moreover, knockdown of a newly identified gland‐associated gene GauGRAS1 caused a glandless phenotype in partial tissues using G. australe. The G. australe genome represents a valuable resource for cotton research and distant relative breeding as well as for understanding the evolutionary history of crop genomes. [ABSTRACT FROM AUTHOR]

Micro RNAs (mi RNAs) are small noncoding RNAs participating in versatile biological processes via post-transcriptionally gene regulation. However, how mi RNAs are modified or degraded remains unknown, despite years of studies have unravelled much details of mi RNA biogenesis and function. Here, we systematically investigated mi RNA modification using six small RNA sequencing libraries generated from cotton seedling as well as cotton fibre at five developmental stages. Our results show that 1-2-nt truncation and addition on both 5′ and 3′ ends of mi RNAs are the major modification forms. The 5′ and 3′ end mi RNA modification was almost equal in the six development stages. Truncation was more common than addition on both 5′ and 3′ end. Structure analysis of the 5′ and 3′ ends of mi RNAs and isomiRs shows that uridine is the preferential nucleotide at the first position of both 5′ and 3′ ends. According to analysis of nucleotides truncated and tailed from mi RNAs, both mi RNAs and isomiRs share a similar positional structure distribution at their 5′ and 3′ ends, respectively. Furthermore, opposite to previous reports, cytodine is more frequently truncated and tailed from the two ends of isomiRs, implying existence of a complex cytodine balance in isomiRs. Comparison of isomiR expression shows differential mi RNA modification amongst the six developmental stages in terms of selective modification form, development-dependent modification and differential expression abundance. Our results globally uncovered mi RNA modification features in cotton, which could contribute us to understanding mi RNA's postmature modification and its regulatory function. [ABSTRACT FROM AUTHOR]

Micro RNAs (mi RNAs) have been found to be differentially expressed during cotton fibre development. However, which specific mi RNAs and how they are involved in fibre development is unclear. Here, using deep sequencing, 65 conserved mi RNA families were identified and 32 families were differentially expressed between leaf and ovule. At least 40 mi RNAs were either leaf or ovule specific, whereas 62 mi RNAs were shared in both leaf and ovule. q RT- PCR confirmed these mi RNAs were differentially expressed during fibre early development. A total of 820 genes were potentially targeted by the identified mi RNAs, whose functions are involved in a series of biological processes including fibre development, metabolism and signal transduction. Many predicted mi RNA-target pairs were subsequently validated by degradome sequencing analysis. GO and KEGG analyses showed that the identified mi RNAs and their targets were classified to 1027 GO terms including 568 biological processes, 324 molecular functions and 135 cellular components and were enriched to 78 KEGG pathways. At least seven unique mi RNAs participate in trichome regulatory interaction network. Eleven trans-acting si RNA (tasi RNA) candidate genes were also identified in cotton. One has never been found in other plant species and two of them were derived from MYB and ARF, both of which play important roles in cotton fibre development. Sixteen genes were predicted to be tasi RNA targets, including sucrose synthase and MYB2. Together, this study discovered new mi RNAs in cotton and offered evidences that mi RNAs play important roles in cotton ovule/fibre development. The identification of tasi RNA genes and their targets broadens our understanding of the complicated regulatory mechanism of mi RNAs in cotton. [ABSTRACT FROM AUTHOR]