Abstract
The KNOX (KNOTTED1-like homeobox) transcription factors play an important role in leaf, shoot apical meristem and seed development and respond to biotic and abiotic stresses. In this study, we analyzed the diversity and evolutionary history of the KNOX gene family in the genome of tetraploid cotton (Gossypium hirsutum). Forty-four putative KNOX genes were identified. All KNOX genes from seven higher plant species were classified into KNOXI, KNOXII, and KNATM clades based on a phylogenetic analysis. Chromosomal localization and collinearity analysis suggested that whole-genome duplication and a polyploidization event contributed to the expansion of the cotton KNOX gene family. Analyses of expression profiles revealed that the GhKNOX genes likely responded to diverse stresses and were involved in cotton growth developmental processes. Silencing of GhKNOX2 enhanced the salt tolerance of cotton seedlings, whereas silencing of GhKNOX10 and GhKNOX14 reduced seedling tolerance to salt stress. Silencing of GhSTM3 influenced the cotton flowering time and plant development. These findings clarify the evolution of the cotton KNOX gene family and provide a foundation for future functional studies of KNOX proteins in cotton growth and development and response to abiotic stresses.
Highlights
Cotton (Gossypium spp.) is the most important natural fiber source worldwide
The GhKNOX genes were named on the basis of the similarity of the encoded amino acid sequence with that of Arabidopsis orthologs; ‘A’ and ‘D’ indicated derivation in the A and D subgenomes, and ‘a’ and ‘b’ were used to distinguish the corresponding paralogs of the same Arabidopsis ortholog
The 44 putative KNOTTED1-like homeobox (KNOX) family genes were named GhKNOX1 to GhKNOX7 and GhSTM1 to GhSTM3, and GhKNL1 was identified in a previous study (Gong et al, 2014)
Summary
Cotton (Gossypium spp.) is the most important natural fiber source worldwide. Gossypium hirsutum, known as allotetraploid cotton, is among the most widely cultivated species and accounts for more than 90% of the global textile fiber production. STM plays an important role in maintenance of apical meristem differentiation and floral development (Takano et al, 2010; Spinelli et al, 2011), broadened plant cell organwide growth and increased leaf complexity (Kierzkowski et al, 2019), and regulates multiple floral fate genes (Roth et al, 2018). Arabidopsis fiber development is promoted by the plant hormone gibberellin and KNAT1, which is repressed by DELLA proteins (FelipoBenavent et al, 2018). KNAT7 interacts with OVATE FAMILY PROTEINS to influence secondary cell wall formation (Li et al, 2011, 2012), and orthologs of KNAT7 expressed to varying degrees in fibrous wood species may explain differences in wood development (Reyes-Rivera et al, 2017). Arabidopsis KNATM, which lacks the homeobox KN domain, is expressed in proximal-lateral domains of organ primordia and at the boundary of mature organs, and functions in leaf proximal-distal patterning (Magnani and Hake, 2008)
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