Genome-Wide Identification and Evolutionary Analysis of Argonaute Genes in Hexaploid Bread Wheat

Abstract

Argonaute (AGO) proteins play a pivotal role in plant growth and development as the core components of RNA-induced silencing complex (RISC). However, no systematic characterization of AGO genes in wheat has been reported to date. In this study, a total number of 69 TaAGO genes in the hexaploid bread wheat (Triticum aestivum cv. Chinese Spring) genome, divided into 10 subfamilies, were identified. Compared to all wheat genes, TaAGOs showed a significantly lower evolutionary rate, which is consistent with their high conservation in eukaryotes. However, the homoeolog retention was remarkably higher than the average, implying the nonredundant biological importance of TaAGO genes in bread wheat. Further homoeologous gene expression bias analyses revealed that TaAGOs may have undergone neofunctionalization after polyploidization and duplication through the divergent expression of homoeologous gene copies, to provide new opportunities for the generation of adaptive traits. Moreover, quantitative real-time polymerase chain reaction (qRT-PCR) analyses indicated that TaAGO gene expression was involved in response to heat, drought, and salt stresses. Our results would provide a theoretical basis for future studies on the biological functions of TaAGO genes in wheat and other gramineous species.

Genome-Wide Identification and Expression Analyses of the Cotton AGO Genes and Their Potential Roles in Fiber Development and Stress Response

“…Accumulating evidence indicates that RNA silencing exerts essential functions in plant resistance to abiotic stresses [ 11 , 13 ]. Therefore, the expression of the GhAGO genes was evaluated after salt and drought treatments.…”

“…For instance, compared with Arabidopsis, subgroups AGO1 and MEL1 (AGO5) expanded in a number of flowering species. More specifically, common bean harbors four AGO10 genes [ 14 ], whereas wheat contains 15 AGO5 paralogs [ 13 ]. In cotton, expansion of AGO5 and AGO10 has been also identified.…”

“…These results suggested that segmental duplication was the primary driving force for the expansion of the GhAGO genes. Similarly, the expansion of wheat AGO genes was dominated by segmental duplication [ 13 ]. Furthermore, all duplicated gene pairs had undergone strong purifying selection in the process of evolution ( Table S4 ), indicating that purifying selection exerted an important role in the formation of the GhAGO gene functions.…”

“…Emerging evidence suggests that the AGO genes not only contribute to biotic stress response, but also modulate plant resistance to abiotic stresses such as salt, drought, cold, and heat stresses [ 8 , 13 , 50 ]. Arabidopsis AtAGO2 was significantly induced by salt stress.…”

“…In general, different numbers of AGO genes are present in various plant species. Ten AGO genes have been revealed in Arabidopsis thaliana [ 4 ], 19 in Oryza sativa [ 5 ], 17 in Zea mays [ 6 ], 15 in Solanum lycopersicum [ 7 ], 13 in Vitis vinifera [ 8 ], 7 in Cucumis sativus [ 9 ], 27 in Brassica napus [ 10 ], 12 in Capsicum annuum [ 11 ], 13 in Citrus sinensis [ 12 ], 69 in Triticum aestivum [ 13 ], 13 in Phaseolus vulgaris [ 14 ], 14 in Solanum tuberosum [ 15 ], 18 in Camellia sinensis [ 3 ], and 13 in Musa acuminata [ 16 ]. However, no AGO genes in Gossypium species have been elucidated to date.…”