Characterization of the KNOTTED1-like HOMEOBOX gene family in kiwifruit and functional analysis of AcKNOX11 related to plant growth, flowering, and melatonin-mediated germination inhibition

KNOX (KNOTTED1-like HOMEOBOX) plays essential roles in extensive plant developmental processes, although information on the KNOX gene has not been documented in kiwifruit (Actinidia chinensis). Here, we identified 19 KNOX gene (AcKNOX) members from the kiwifruit genome. The AcKNOX could be divided into three categories, and most members contain four conserved domains. AcKNOX promoters contain abundant CREs that respond to hormonal and stress cues. AcKNOX genes express in multiple tissues, and some of these genes respond to salt stress. It has been found in this study that AcKNOX11, selectively expressed in flower bud and shoot, activated during the lateral bud development and could be evoked by ABA and melatonin treatments. The AcKNOX11 protein located in the nucleus can be predicted to interact with other protein partners. Functional analysis revealed that AcKNOX11 delayed flowering, reduced plant height, altered leaf shape, and inhibited seed germination by ABA-melatonin crosstalk in Arabidopsis. This first thorough analysis of the AcKNOX genes will provide a more in-depth understanding of AcKNOX genes in kiwifruit and lay important theoretical basis for future functional dissection.