Cytokinin: a key driver of seed yield

Abstract

The cytokinins have been implicated in many facets of plant growth and development including cell division and differentiation, shoot and root growth, apical dominance, senescence, fruit and seed development, and the response to biotic and abiotic stressors. Cytokinin levels are regulated by a balance between biosynthesis [isopentenyl transferase (IPT)], activation [Lonely Guy (LOG)], inactivation (O-glucosyl transferase), re-activation (β-glucosidase), and degradation [cytokinin oxidase/dehydrogenase (CKX)]. During senescence, the levels of active cytokinins decrease, with premature senescence leading to a decrease in yield. During the early stages of fruit and seed development, cytokinin levels are transiently elevated, and coincide with nuclear and cell divisions which are a determinant of final seed size. Exogenous application of cytokinin, ectopic expression of IPT, or down-regulation of CKX have, on occasions, led to increased seed yield, leading to the suggestion that cytokinin may be limiting yield. However, manipulation of cytokinins is complex, not only because of their pleiotropic nature but also because the genes coding for biosynthesis and metabolism belong to multigene families, the members of which are themselves spatially and temporally differentiated. Previous research on yield of rice showed that plant breeders could directly target the cytokinins. Modern genome editing tools could be employed to target and manipulate cytokinin levels to increase seed yield with the concurrent aim of maintaining quality. However, how the cytokinin level is modified and whether IPT or CKX is targeted may depend on whether the plant is considered to be in a source-limiting environment or to be sink limited.

Infection byRhodococcus fasciansmaintains cotyledons as a sink tissue for the pathogen

“…For many years, the cytokinins have been functionally implicated in source-sink dynamics during plant development (Mothes and Engelbrecht, 1963;Ehness et al, 1997;Balibrea Lara et al, 2004;Werner and Schmülling, 2009;Jameson and Song, 2016), as well as being implicated in plant-pathogen (bacteria, fungal and viral) interactions and particularly in the establishment of a suitable niche for gall-forming pathogens (Jameson, 2000). In plants, cytokinins are biosynthesized directly by isopentenyl transferase (IPT) attaching an isoprenoid side chain to the N6 position of an adenine nucleotide moiety.…”

“…Enhanced expression of CWINV has been reported in several plant-pathogen interactions (Berger et al, 2007;Depuydt et al, 2009;Chandran et al, 2010;Siemens et al, 2011). Interaction between cytokinins and CWINV is well documented, in relation to both cell division (Roitsch and Gonz alez, 2004;Jameson and Song, 2016) and source-sink dynamics (Ehneß and Roitsch, 1997;Albacete et al, 2015). Cytokinins failed to delay senescence when CWINV was inhibited (Balibrea Lara et al, 2004), indicating that nutrient mobilization is essential in cytokinin-induced senescence delay, providing the basis for pathogen-induced 'Green Island' formation (Roitsch and Gonz alez, 2004), and potentially the greening of the infected pea cotyledons.…”

Cytokinins and Expression of SWEET, SUT, CWINV and AAP Genes Increase as Pea Seeds Germinate

“…The cytokinins are clearly implicated in seed development [41]. The cytokinins are biosynthesised by isopentenyl transferase (IPT), degraded by cytokinin oxidase/dehydrogenase (CKX), and conjugated to storage or inactivated forms by glycosidases.…”

“…As transporter genes (reviewed in [10,53]), and cytokinin biosynthetic and degradative genes (reviewed in [41]) are the targets of transgenic approaches to increasing seed quality and/or quantity, we were interested if these gene families were expressed during germination. Such knowledge is important as changes in the expression of genes in the parental generation may impact seed germination and seedling vigour of the subsequent generation.…”

Applications and roles of the CRISPR system in genome editing of plants

“…Basak and Nithin 2015;Duan et al 2015;Jameson and Song 2015;Jiang et al 2013;Lowder et al 2015;Ma et al 2015; Mikami et al 2015a, b;Schiml et al 2014;Seo et al 2015;Shan et al 2014;Sugano et al 2014;Wang et al 2015;Woo et al 2015;Xie et al 2015;Xie and Yang 2013;Xu et al 2014;Zhang et al 2016b;Zhang et al 2014; Zhou et al Gao et al 2015a;Li et al 2014; Upadhyay et al Ali et al 2015;Jiang et al 2013;Johnson et al 2015;Lowder et al 2015;Nekrasov et al 2013;Upadhyay et al 2013) MaizeZea mays ZmPDS, ZmIPK1A, ZmIPK, ZmMRP4 Liguleless1 (LIG1) gene, male fertility genes (Ms26 and Ms45), acetolactate synthase (ALS) genes (ALS1 and ALS2)(Basak and Nithin 2015; Liang et al 2014; Puchta and Fauser 2013; Schuster et al 2015; Svitashev et al 2015; Xing et al Basak and Nithin 2015; Shan et al 2014; Sugano et al 2014; Upadhyay et al 2013; Wang et al 2014) Soybean Glycine max Green fluorescent protein (GFP) transgene GmPDS11GmPDS18(Du et al 2016;Jacobs et al 2015;Michno et al 2015;Ricroch and Henard-Damave 2015) Potato Solanum tuberosum Cas1, Cas3, and the four subtype specific proteins Csy1, Csy2, Csy3 and Cas6f (Csy4) Phytophthora infestans resistance genes(Butler et al 2015;Richter et al 2012; Schaart et al glucuronidase (GUS) transgene(Michno et al 2015) …”