No abstract

SUMMARYTrichomes, the outward projection of plant epidermal tissue, provide an effective defense against stress and insect pests. Although numerous genes have been identified to be involved in trichome development, the molecular mechanism for trichome cell fate determination is not well enunciated. Here, we reported GoSTR functions as a master repressor for stem trichome formation, which was isolated by map‐based cloning based on a large F2 segregating population derived from a cross between TM‐1 (pubescent stem) and J220 (smooth stem). Sequence alignment revealed a critical G‐to‐T point mutation in GoSTR's coding region that converted codon 2 from GCA (Alanine) to TCA (Serine). This mutation occurred between the majority of Gossypium hirsutum with pubescent stem (GG‐haplotype) and G. barbadense with glabrous stem (TT‐haplotype). Silencing of GoSTR in J220 and Hai7124 via virus‐induced gene silencing resulted in the pubescent stems but no visible change in leaf trichomes, suggesting stem trichomes and leaf trichomes are genetically distinct. Yeast two‐hybrid assay and luciferase complementation imaging assay showed GoSTR interacts with GoHD1 and GoHOX3, two key regulators of trichome development. Comparative transcriptomic analysis further indicated that many transcription factors such as GhMYB109, GhTTG1, and GhMYC1/GhDEL65 which function as positive regulators of trichomes were significantly upregulated in the stem from the GoSTR‐silencing plant. Taken together, these results indicate that GoSTR functions as an essential negative modulator of stem trichomes and its transcripts will greatly repress trichome cell differentiation and growth. This study provided valuable insights for plant epidermal hair initiation and differentiation research.

Verticillium, representing one of the world’s major pathogens, causes Verticillium wilt in important woody species, ornamentals, agricultural, etc., consequently resulting in a serious decline in production and quality, especially in cotton. Gossupium hirutum and Gossypium barbadense are two kinds of widely cultivated cotton species that suffer from Verticillium wilt, while G. barbadense has much higher resistance toward it than G. hirsutum. However, the molecular mechanism regarding their divergence in Verticillium wilt resistance remains largely unknown. In the current study, G. barbadense cv. Hai7124 and G. hirsutum acc. TM-1 were compared at 0, 12, 24, 48, 72, 96, 120, and 144 h post-inoculation (hpi) utilizing high throughput RNA-Sequencing. As a result, a total of 3,549 and 4,725 differentially expressed genes (DEGs) were identified, respectively. In particular, the resistant type Hai7124 displayed an earlier and faster detection and signaling response to the Verticillium dahliae infection and demonstrated higher expression levels of defense-related genes over TM-1 with respect to transcription factors, plant hormone signal transduction, plant-pathogen interaction, and nucleotide-binding leucine-rich repeat (NLR) genes. This study provides new insights into the molecular mechanisms of divergence in Verticillium wilt resistance between G. barbadense and G. hirsutum and important candidate genes for breeding V. dahliae resistant cotton cultivars.

Short tandem repeats (STRs), which vary in size due to featuring variable numbers of repeat units, are present throughout most eukaryotic genomes. To date, few population-scale studies identifying STRs have been reported for crops. Here, we constructed a high-density polymorphic STR map by investigating polymorphic STRs from 911 Gossypium hirsutum accessions. In total, we identified 556,426 polymorphic STRs with an average length of 21.1 bp, of which 69.08% were biallelic. Moreover, 7,718 (1.39%) were identified in the exons of 6,021 genes, which were significantly enriched in transcription, ribosome biogenesis, and signal transduction. Only 5.88% of those exonic STRs altered open reading frames, of which 97.16% were trinucleotide. An alternative strategy STR-GWAS analysis revealed that 824 STRs were significantly associated with agronomic traits, including 491 novel alleles that undetectable by previous SNP-GWAS methods. For instance, a novel polymorphic STR consisting of GAACCA repeats was identified in GH_D06G1697, with its (GAACCA)5 allele increasing fiber length by 1.96–4.83% relative to the (GAACCA)4 allele. The database CottonSTRDB was further developed to facilitate use of STR datasets in breeding programs. Our study provides functional roles for STRs in influencing complex traits, an alternative strategy STR-GWAS for allele mining, and a database serving the cotton community as a valuable resource.