Cytokinin oxidase/dehydrogenase OsCKX11 coordinates source and sink relationship in rice by simultaneous regulation of leaf senescence and grain number

Abstract

Summary The flag leaf and grain belong to the source and sink, respectively, of cereals, and both have a bearing on final yield. Premature leaf senescence significantly reduces the photosynthetic rate and severely lowers crop yield. Cytokinins play important roles in leaf senescence and determine grain number. Here, we characterized the roles of the rice (Oryza sativa L.) cytokinin oxidase/dehydrogenase OsCKX11 in delaying leaf senescence, increasing grain number, and coordinately regulating source and sink. OsCKX11 was predominantly expressed in the roots, leaves, and panicles and was strongly induced by abscisic acid and leaf senescence. Recombinant OsCKX11 protein catalysed the degradation of various types of cytokinins but showed preference for trans‐zeatin and cis‐zeatin. Cytokinin levels were significantly increased in the flag leaves of osckx11 mutant compared to those of the wild type (WT). In the osckx11 mutant, the ABA‐biosynthesizing genes were down‐regulated and the ABA‐degrading genes were up‐regulated, thereby reducing the ABA levels relative to the WT. Thus, OsCKX11 functions antagonistically between cytokinins and ABA in leaf senescence. Moreover, osckx11 presented with significantly increased branch, tiller, and grain number compared with the WT. Collectively, our findings reveal that OsCKX11 simultaneously regulates photosynthesis and grain number, which may provide new insights into leaf senescence and crop molecular breeding.

TaCKX2.2 Genes Coordinate Expression of Other TaCKX Family Members, Regulate Phytohormone Content and Yield-Related Traits of Wheat

“…However, the same effect of increased grain number in rice was obtained by silencing or knocking-out OsCKX2 [30]. OsCKX11, orthologous to wheat TaCKX11, which is expressed in all organs of the wheat plant [12,32], coordinated sink-source relationships and leaf senescence and grain number in rice [38].…”

Low Light/Darkness as Stressors of Multifactor-Induced Senescence in Rice Plants

“…Knock-out mutant ( osckx ) reversely promoted the cytokinins and ABA levels, and exhibited a significant increase in cytokinins levels as compared to WT during dark treatment. On the contrary, decreases in ABA levels were noted, accompanied by down-regulation of ABA-biosynthesizing genes and up-regulation of ABA-degrading genes in the osckx11 mutant as compared to the WT [ 56 ]. Similarly, the expressions of ABA-signaling and biosynthesizing genes were significantly down-regulated in osmyb102-D and up-regulated in rice myeloblastosis 102 (OsMYB102)-overexpressing lines, which were accompanied by the activation of abscisic acid 8′-hydroxylase 2-like (ABA8OX2 ), which functions in the ABA catabolic pathway.…”

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

“…In Arabidopsis, AtCKX7 displays high affinity toward cZ (Gajdosova et al., 2011) while the gain‐of‐function mutant of AtCKX7 exhibited an increased CKX enzymatic activity, leading to CK deficiency and altered vascular development (Köllmer et al., 2014). OsCKX11 coordinates source and sink relationship, thus regulating leaf senescence and grain number in rice (Zhang et al., 2020). In soybean, GmCKX7‐1 and GmCKX7‐ 3 were highly expressed in the leaves, roots, and root hairs at reproductive stage under normal and drought conditions (Le et al., 2012).…”