The soybean (Glycine max L.) cytokinin oxidase/dehydrogenase multigene family; Identification of natural variations for altered cytokinin content and seed yield

Abstract

Cytokinins (CKs) play a fundamental role in regulating dynamics of organ source/sink relationships during plant development, including flowering and seed formation stages. As a result, CKs are key drivers of seed yield. The cytokinin oxidase/dehydrogenase (CKX) is one of the critical enzymes responsible for regulating plant CK levels by causing their irreversible degradation. Variation of CKX activity is significantly correlated with seed yield in many crop species while in soybean (Glycine max L.), the possible associations between CKX gene family members (GFMs) and yield parameters have not yet been assessed. In this study, 17 GmCKX GFMs were identified, and natural variations among GmCKX genes were probed among soybean cultivars with varying yield characteristics. The key CKX genes responsible for regulating CK content during seed filling stages of reproductive development were highlighted using comparative phylogenetics, gene expression analysis and CK metabolite profiling. Five of the seventeen identified GmCKX GFMs, showed natural variations in the form of single nucleotide polymorphisms (SNPs). The gene GmCKX7‐1, with high expression during critical seed filling stages, was found to have a non‐synonymous mutation (H105Q), on one of the active site residues, Histidine 105, previously reported to be essential for co‐factor binding to maintain structural integrity of the enzyme. Soybean lines with this mutation had higher CK content and desired yield characteristics. The potential for marker‐assisted selection based on the identified natural variation within GmCKX7‐1, is discussed in the context of hormonal control that can result in higher soybean yield.

Cytokinin glucosyl transferases, key regulators of cytokinin homeostasis, have potential value for wheat improvement

“…There is increasing interest in the plant hormone group, the cytokinins, because of their potential to improve crop yield (e.g. Chen et al, 2020b;Cucinotta et al, 2018;Jabło nski et al, 2020;Jameson and Song, 2020;Nguyen et al, 2020Nguyen et al, , 2021Schwarz et al, 2020;Wang et al, 2020a;Zhang et al, 2020). The cytokinins are considered to have significant but contrasting roles in shoot and root architecture (Werner et al, 2003a) and to control both seed number and seed size (Jameson and Song, 2016).…”

“…Joshi et al, 2019;Rivero et al, 2010) or enhancement of root growth (e.g. Khandal et al, 2020;Nehnevajova et al, 2019;Werner et al, 2010;Zhang et al, 2020;and reviewed in Chen et al, 2020b). While there has been considerable interest in modifying cytokinin levels in plants by targeting either biosynthesis (via isopentenyl transferase, IPT) or cytokinin destruction (via by cytokinin oxidase/dehydrogenase, CKX), much less attention has been given to manipulating the The isoprenoid cytokinins are generated in plant tissues predominantly via two pathways: de novo biosynthesis via ADP/ ATP isopentenyl transferases (IPTs) and, indirectly, through the degradation of specific isoprenylated tRNA species Miyawaki et al, 2006) (Figure 1).…”

Cytokinin Oxygenase/Dehydrogenase Inhibitors: An Emerging Tool in Stress Biotechnology Employed for Crop Improvement

“…The primary approaches to decrease the expression of CKX enzyme can either be through chemical means ( Kopecný et al, 2010 ; Nisler et al, 2021 ) and molecular approaches ( Gouda et al, 2020a ; Nguyen et al, 2021 ). Figure 1 represents a schematic diagram on the mechanism of CKO/CKX control.…”

“…An increase in growth, chlorophyll content and grain yield were observed in this case. Recently, one of the molecular approaches applied specific missense single nucleotide polymorphisms (SNPs), namely SNP42, SNP43, SNP44, and SNP46 to reduce the expression of CKX enzyme in rice that led to increase in grain numbers ( Gouda et al, 2020a ), while another nine SNPs from five genes were demarcated in soybean for enhanced seed yield ( Nguyen et al, 2021 ). In a new approach, computational means has also been followed to study the “structure, function and interaction” of the CKX enzyme from rice plants for the first time ( Gouda et al, 2020b ).…”

“…However, an appropriate dosage level as well as the “cost effectiveness” of these chemicals is yet to be assessed at a commercial level, thereby warranting immediate attention from the researchers in this field. Recent studies demonstrate the emergence of successful genetic approaches ( Wang et al, 2020 ; Nguyen et al, 2021 ; Nisler et al, 2021 ; and many others), emphasizing that modulating CKX enzymes can open up multiple paths for developing “tailor made” stress resistant and nutrition rich crops which will be useful in the long-term breeding programs ( Ramireddy et al, 2018 ). These will be developed as a means of sustainable agriculture through unravelling the signaling network of the cytokinins ( Pavlů et al, 2018 ).…”