TABLE 2.

Genetic manipulation of CKX genes in different plant species for increasing seed yield output.

S.No.	Name of CKX gene	Source species	Target species	Type of genetic manipulation	Observed changes in yield-related parameters	Comments	References
1	OsCKX2	Oryza sativa	Oryza sativa	Natural genetic variation	Panicle branches ↑		Ashikari et al. (2005)
					grain number per panicle ↑
					Total grain number ↑
				RNAi mediated gene knockdown	Number of tillers ↑	Delayed Leaf senescence (DLS) phenotype in transgenic lines	Yeh et al. (2015)
					Number of panicles ↑
					Grains per plant ↑
					TGW ↑
					Total grain yield per plant ↑
					Plant height ↑	Reduced yield loss in transgenic lines under salinity stress compared to control lines	Joshi et al. (2018)
					Filled grains per panicle ↑
					Panicle number ↑
					Harvest index ↑
					TGW ↑
					Leaf senescence ↑
				CRISPR/Cas9 mediated gene knockout	Plant height ↑	Effect on seed yield output not reported	Li et al. (2016)
					Panicle length ↑
					Flower number per panicle↑
				EMS mutagenesis is followed by Map-based cloning	Panicle length ↑		Tsago et al. (2020)
					Panicle branches ↑
					Filled grains per plant ↑
					Grain length ↑
					TGW ↑
					Seed setting rate ↑
2	OsCKX11	Oryza sativa	Oryza sativa	CRISPR/Cas9 mediated gene knockout	Tiller’s number ↑	OsCKX11 is involved in the regulation of both leaf senescence and seed yield	Zhang et al. (2021)
					Grains per panicle ↑
					Grains per plant ↑
					Fertility rate ↓
					TGW ↓
					Leaf senescence ↓
3	TaCKX1	Triticum aestivum	Triticum aestivum	RNAi mediated gene knockdown	Number of spikes ↑		Li et al. (2018)
					Grain yield ↑
					TGW ↓
4	HvCKX1	Hordeum vulgare	Hordeum vulgare	RNAi mediated gene knockdown	Spikes number ↑		Holubová et al. (2018)
					Grains per plant ↑
					Overall grain yield ↑
					TGW ↓
5	HvCKX1 and HvCKX3	Hordeum vulgare	Hordeum vulgare	CRISPR/Cas9 mediated gene knockout	In one ckx3 mutant line	Activation of strong cytokinin homeostatic response resulted in reduced expression of CK biosynthetic genes and increased CK inactivation through O-glucosylation	Gasparis et al. (2019)
					Spikes number ↑
					In other mutant lines
					Grain number ↓
					Grain weight ↓
6	CKX3/CKX5	Arabidopsis thaliana	Arabidopsis thaliana	ckx3ckx5 double mutant generated by random T-DNA mutagenesis	Flowers number per plant ↑	ckx3 or ckx5 mutations alone were not sufficient to alter yield components significantly	Bartrina et al. (2011a)
					Flower size ↑
					Gynoecium size ↑
					Inflorescence meristem size ↑
					Ovules per gynoecium ↑
					Siliques per plant ↑
					Seed number per silique ↑
					Overall seed yield ↑
		Brassica napus	Brassica napus	ckx3ckx5 sextuple mutant generated by random T-DNA mutagenesis and TILLING.	Inflorescence meristem size ↑	The number of seeds per silique was equivalent to wild type because of high seed mortality	Schwarz et al. (2020)
					Floral primordia number ↑
					Flower number per plant ↑
					Gynoecium size ↑
					Ovules per gynoecium ↑
					Seed weight and number ↑
					TGW ↑
7	MtCKX3	Medicago truncatula	Medicago truncatula	Tnt1 retrotransposon tagged insertion mutants	Length of primary root ↑	Single mutants of any other CKX gene did not exhibit significant deviation from wild-type phenotype, indicating functional redundancy	Wang et al. (2021)
					Lateral roots number ↓

^#’↑’ and ‘↓’ symbols respectively indicate increase and decrease in corresponding parameter.