Expression Patterns of HvCKX Genes Indicate Their Role in Growth and Reproductive Development of Barley

Abstract

Cytokinin oxidase/dehydrogenase proteins (CKX) are encoded by a multigene family of CKX genes with a varying number of members depending on species. For some of the genes, spectacular effects on grain production in selected cereals have been observed. Despite the fact that partial or full length sequences of most HvCKX genes in barley (Hordeum vulgare) have already been published, in most cases their specific biological functions have not been reported. Detailed expression patterns for five HvCKX genes in different organs/tissues of developing barley plants coupled with analysis of RNAi silent for two genes are presented to test the hypothesis that these expression profiles might indicate their function. Elevated expression for four of them – HvCKX1, HvCKX9, HvCKX4, and HvCKX11 – was found in developing kernels of wild-type plants compared to other tissues. HvCKX5 was mainly expressed in leaf tissue. Lower expression was noted for HvCKX1 in seedling roots and for HvCKX9 in leaves. The documented effect of RNAi silencing of HvCKX1 and a trend for HvCKX9 was higher plant productivity, and the trait was inherited through four generations. Higher plant yield was determined by higher numbers of seeds and spikes. Increased productivity was significantly greater in HvCKX1 silenced plants showing higher relative expression of HvCKX1 in developing kernels of wild-type plants compared to the expression of HvCKX9. Both HvCKX1 silenced T1 seedlings of cv. Golden Promise and the newly transformed breeding line STH7308 showed greater root mass, but this trait was not inherited in the next generation. Similarly HvCKX9 silenced T1 seedlings exhibited greater plant height without inheritance in the next generation. It is suggested that these effects were not inherited because of compensation by other genes co-ordinately regulating reproductive development. One line with untypically changed, inherited phenotype, which was selected from several dozen silenced lines showing stable and common phenotypes is presented.

Silencing ofTaCKX1mediates expression of otherTaCKXgenes to increase grain yield in wheat

“…Knock-out mutation or silencing by RNAi of OsCKX2 in rice significantly increased grain number (Ashikari et al, 2005). The same effect of elevated grain number, spike number and yield was reported for RNAi-silenced HvCKX1 in barley (Zalewski et al, 2010; Zalewski et al, 2012; Zalewski et al, 2014) and repeated for the same gene under field conditions (Holubova et al, 2018). Moreover, significantly increased grain number per spike was found as the effect of the TaCKX2.4 gene silenced by RNAi (Li et al, 2018).…”

“…Active CKs can be metabolized via oxidation by cytokinin oxidase/dehydrogenase (CKX) or by activity of glycosyltransferases. Many reports have demonstrated that the irreversible degradation step by CKX enzyme plays an important role in regulation of cytokinin level in some cereals: maize (Brugiè re N, 2003), rice (Ashikari et al, 2005), barley (Zalewski et al, 2010; Zalewski et al, 2014) and wheat (Song et al, 2012; Zhang et al, 2012; Ogonowska et al, 2019).…”

MtNF-YA1, A Central Transcriptional Regulator of Symbiotic Nodule Development, Is Also a Determinant of Medicago truncatula Susceptibility toward a Root Pathogen

“…Among them 2 genes coding for cytokinin- O -glucosyltransferases (ZOG), i.e., Medtr6g014660 and Medtr3g111140.1 and a gene coding for a cytokinin oxidase, i.e., Medtr4g118430.1 are significantly downregulated in Mtnf-ya1-1 roots compared to WT (A17) roots, both before inoculation and one day after inoculation. In Rice the suppression of ZOGs leads to a decrease in fasciculated root production (Kudo et al, 2012) while contradicting reports about the positive and negative effect of cytokinin oxidase on root growth exist (Köllmer et al, 2014; Zalewski et al, 2014). …”

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

“…As decreasing CKX activity is a target for enhancing yield in both monocots and dicots [41,62,63] it is important to be aware that any increased cytokinin may impact source-sink relationships. Particularly critical in peas may be PsCKX2, which is expressed in the imbibing seed: if this gene family member were to be down-regulated, this may impact severely on the release of nutrients from the cotyledon.…”