Biochemical and molecular characterisation of exogenous cytokinin application on grain filling in rice

Abstract

BackgroundPoor filling of grains in the basal spikelets of large size panicles bearing numerous spikelets has been a major limitation in attempts to increase the rice production to feed the world’s increasing population. Considering that biotechnological intervention could play important role in overcoming this limitation, the role of cytokinin in grain filling was investigated based on the information on cell proliferating potential of the hormone and reports of its high accumulation in immature seeds.ResultsA comparative study considering two rice varieties differing in panicle compactness, lax-panicle Upahar and compact-panicle OR-1918, revealed significant difference in grain filling, cytokinin oxidase (CKX) activity and expression, and expression of cell cycle regulators and cytokinin signaling components between the basal and apical spikelets of OR-1918, but not of Upahar. Exogenous application of cytokinin (6-Benzylaminopurine, BAP) to OR-1918 improved grain filling significantly, and this was accompanied by a significant decrease in expression and activity of CKX, particularly in the basal spikelets where the activity of CKX was significantly higher than that in the apical spikelets. Cytokinin application also resulted in significant increase in expression of cell cycle regulators like cyclin dependent kinases and cyclins in the basal spikelets that might be facilitating cell division in the endosperm cells by promoting G1/S phase and G2/M phase transition leading to improvement in grain filling. Expression studies of type-A response regulator (RR) component of cytokinin signaling indicated possible role of OsRR3, OsRR4 and OsRR6 as repressors of CKX expression, much needed for an increased accumulation of CK in cells. Furthermore, the observed effect of BAP might not be solely because of it, but also because of induced synthesis of trans-zeatin (tZ) and N6-(Δ2-isopentenyl)adenine (iP), as reflected from accumulation of tZR (tZ riboside) and iPR (iP riboside), and significantly enhanced expression of an isopentenyl transferase (IPT) isoform.ConclusionThe results suggested that seed-specific overexpression of OsRR4 and OsRR6, and more importantly of IPT9 could be an effective biotechnological intervention towards improving the CK level of the developing caryopses leading to enhanced grain filling in rice cultivars bearing large panicles with numerous spikelets, and thereby increasing their yield potential.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1279-4) contains supplementary material, which is available to authorized users.

OsCYP71D8L as a key regulator involved in growth and stress response by mediating gibberellins and cytokinins homeostasis in rice

“…Similarly, OsMCA1 is involved in the deactivation of bioactive GA, and its mutation results in GA-deficient phenotypes with shorter root and reduced height (Liu et al 2015). In rice, cytokinin is essential for the control of entire life cycle including root development, shoot meristem activity, vegetative and reproductive branching, spikelets per panicle, and grain production(Ashikari et al, 2005; Du et al, 2017; Gao et al, 2014; Gu et al, 2015; Jiang et al, 2017; Kurakawa et al, 2007; Li et al, 2013; Ohashi et al, 2017; Panda et al, 2018; Wu et al, 2017; Wu et al, 2016; Zhao et al, 2015). For examples, cytokinin receptor OsCKT1 is necessary for the regulation of root development, and Osckt1 exhibits insensitivity to cytokinin treatment with normal root growth (Ding et al, 2017).…”

“…In comparison, it is also feasible to genetically improve crop yield by modulating CK homeostasis. For examples, exogenous CK could increase rice yield potential by enhancing grain filling and bearing large panicles (Panda et al, 2018). Downregulation of OsCKX2 and OscZOG1 resulted in elevated CKs, and thereby improved yield-related traits including tiller numbers, panicle branches, and grain number per panicle in rice (Ashikari et al, 2005; Shang et al, 2016).…”

Identification and expression analysis of miRNAs and elucidation of their role in salt tolerance in rice varieties susceptible and tolerant to salinity

“…Complete CDS of the individual targets was retrieved from the NCBI site and searched for similarity in the Oryza sativa L. indica database using BLAST programme at the EnsemblPlants resource database (http://plants.ensembl.org/index.html). The search at the EnsemblePlants resource was to ensure that the target sequence was present in the Indica variety as well [83,84].…”

Silencing ofTaCKX1mediates expression of otherTaCKXgenes to increase grain yield in wheat

“…There is growing evidence on their key role in seed yield regulation (reviewed by Jameson and Song, 2016). In cereals and grasses an increased content of CKs has been reported to positively affect sink potential in developing grains (Liu et al, 2013), maintain leaf chlorophyll status during plant senescence (Zhang et al, 2016) and grain filling (Panda et al, 2018). Moreover, in wheat the CKs take part in regulation of seed dormancy (Chitnis et al, 2014).…”