Abstract:

Phosphorus (P) is an essential nutrient element for plant growth and development. Low phosphorus stress is one of the important factors restricting the growth and development of cotton. In this study, 419 core accessions of upland cotton were used as test materials. Phenotypic identification of six root biomass related traits at the seedling stage in two environments were carried out. Genome-wide association study was used to screen the significantly associated SNPs (single nucleotide polymorphisms) and candidate genes with 3.66 million SNPs. The results showed that there were extensive genetic variations in root biomass traits of cotton under low P stress, among which the coefficient of variation of root shoot ratio was the largest (45.30%). A total of 393 SNPs were significantly associated with root biomass traits, and these loci mainly distributed in chromosome D02 (75), A08 (64) and A07 (35), among which a total of 28 SNPs were detected in two traits or environments at least. 13 candidate genes were further screened, among which Gh_A08G1889 was detected in the RSR under low phosphorus conditions in E1 environment (LP-RSR-E1), and A08:99606874 (A/C) was located in the exon of this gene, leading to non-synonymous mutation (Val/Leu). Moreover, the gene encoding protein GID1C (Gibberellin receptor GID1C) can interact with DELLA protein to participate in the GA metabolic pathway, which can control the growth and development of plant roots and respond to environmental stress. Gh_D08G2527 was detected in both root dry weight (RDW) and total dry weight (TDW) in E2 environments (LP-RDW-E2 and LP-TDW-E2). The DREB3 (Dehydration-responsive element-binding protein 3) transcription factors encoded by this gene were involved in the response process of environmental stress in a variety of crops, and DREB could specifically combine with DRE to induce the expression of environmental stress response genes and produce plant stress resistance. The results of qRT-PCR revealed that the relative expression of Gh_D08G2527 in low phosphorus tolerant varieties was significantly higher than that in low phosphorus sensitive varieties under low phosphorus treatment. These results of this study provide theoretical reference and genetic resources for further understanding the molecular mechanism of low phosphorus stress in cotton.

Key words: cotton, low phosphorus stress, root biomass related traits, SNP, GWAS, candidate gene, qRT-PCR