Silencing ofTaCKX1mediates expression of otherTaCKXgenes to increase grain yield in wheat

AbstractTaCKXfamily genes influence development of wheat plants by specific regulation of cytokinin content in different organs. However, their detailed role is not known. TheTaCKX1, highly and specifically expressed in developing spikes and in seedling roots, was silenced by RNAi-mediated gene silencing viaAgrobacteriumand the effect of silencing was investigated in 7 DAP spikes of T1and T2generations. Various levels ofTaCKX1silencing in both generations influence different models of co-expression with otherTaCKXgenes and parameters of yield-related traits. Only a high level of silencing in T2resulted in strong down-regulation ofTaCKX11 (3), up-regulation ofTaCKX2.1,2.2,5and9(10), and a high yielding phenotype. This phenotype is characterised by higher spike number, grain number and grain yield, as well as slightly higher mass of seedling roots, but lower thousand grain weight (TGW) and slightly lower spike length. Content of most of cytokinin forms in 7 DAP spikes of silenced T2lines increased from 40 to 76% compared to the non-silenced control. The CKs cross talk with other phytohormones.Each of the tested yield-related traits is regulated by various up- or down-regulatedTaCKXgenes and phytohormones. Unexpectedly, increased expression ofTaCKX2.1in silent forTaCKX1T2plants up-regulated trans- and cis-zeatin and trans-zeatin glucosides, determining lower TGW and chlorophyll content in flag leaves but higher grain yield. The coordinated effect ofTaCKX1silencing on expression of otherTaCKXgenes, phytohormone levels in 7 DAP spikes and yield-related traits in silenced T2lines is presented.One-sentence summaryDifferent levels ofTaCKX1silencing influence various models of coordinated expression ofTaCKXgenes and phytohormone levels in 7 DAP spikes, as well as yield parameters.