Abstract
Cytokinins (CKs) are involved in determining the final grain yield in wheat. Multiple gene families are responsible for the controlled production of CKs in plants, including isopentenyl transferases for de novo synthesis, zeatin O-glucosyltransferases for reversible inactivation, β-glucosidases for reactivation, and CK oxidases/dehydrogenases for permanent degradation. Identifying and characterizing the genes of these families is an important step in furthering our understanding of CK metabolism. Using bioinformatics tools, we identified four new TaIPT, four new TaZOG, and 25 new TaGLU genes in common wheat. All of the genes harbored the characteristic conserved domains of their respective gene families. We renamed TaCKX genes on the basis of their true orthologs in rice and maize to remove inconsistencies in the nomenclature. Phylogenetic analysis revealed the early divergence of monocots from dicots, and the gene duplication event after speciation was obvious. Abscisic acid-, auxin-, salicylic acid-, sulfur-, drought- and light-responsive cis-regulatory elements were common to most of the genes under investigation. Expression profiling of CK metabolic gene families was carried out at the seedlings stage in AA genome donor of common wheat. Exogenous application of phytohormones (6-benzylaminopurine, salicylic acid, indole-3-acetic acid, gibberellic acid, and abscisic acid) for 3 h significantly upregulated the transcript levels of all four gene families, suggesting that plants tend to maintain CK stability. A 6-benzylaminopurine-specific maximum fold-change was observed for TuCKX1 and TuCKX3 in root and shoot tissues, respectively; however, the highest expression level was observed in the TuGLU gene family, indicating that the reactivation of the dormant CK isoform is the quickest way to counter external stress. The identification of new CK metabolic genes provides the foundation for their in-depth functional characterization and for elucidating their association with grain yield.
Highlights
Wheat (Triticum aestivum L.) is the predominant cereal crop, second only to rice as the most important staple, with global production nearing 740 million tons of grain (USDA, 2017)
Genetic manipulation of the genes involved in CK homeostasis can be used for yield improvement, as a significant change in CK content has been observed during grain development in crop plants, including wheat (Jameson, McWha & Wright, 1982) and rice (Ashikari et al, 2005)
Seedlings were treated with plant hormones: 5 μM 6-benzylaminopurine (6-BA), 0.5 mM salicylic acid (SA), 10 μM indole-3-acetic acid (IAA), 30 μM gibberellic acid (GA3), and 10 μM abscisic acid (ABA) for 3 h, along with the control treatment
Summary
Wheat (Triticum aestivum L.) is the predominant cereal crop, second only to rice as the most important staple, with global production nearing 740 million tons of grain (USDA, 2017). The projected increase in the human population will increase the production demand to 900 million tons by 2050 (FAO, 2016); increasing the yield per unit area will be important for meeting this mounting challenge (Bartrina et al, 2011). Genetic manipulation of the genes involved in CK homeostasis can be used for yield improvement, as a significant change in CK content has been observed during grain development in crop plants, including wheat (Jameson, McWha & Wright, 1982) and rice (Ashikari et al, 2005). CK homeostasis is carried out by several gene families including isopentenyl transferases (IPTs) for biosynthesis, zeatin O-glucosyltransferases (ZOGs) for reversible inactivation, β-glucosidases (GLUs) for reactivation, and cytokinin oxidases/dehydrogenases (CKXs) for degradation (Song, Jiang & Jameson, 2012)
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