Two citrus KNAT-like genes, CsKN1 and CsKN2, are involved in the regulation of spring shoot development in sweet orange

Abstract

Shoot tip abortion is a very common phenomenon in some perennial woody plants that affects the height, architecture, and branch orientation of trees. To date, little is known about the mechanism of shoot tip abortion. In this study, a sweet orange gene encoding a KNAT-like protein (CsKN1) was identified and showed high expression in the shoot apical meristem (SAM). Overexpression of CsKN1 prolonged the vegetative growth of SAM, and silencing of CsKN1 resulted in the loss or inhibition of SAM in transgenic plants. Yeast two-hybrid analysis revealed that CsKN1 interacted with another citrus KNAT-like protein (CsKN2), and overexpression of CsKN2 in lemon and tobacco caused an extremely multiple meristem phenotype. Overexpression of CsKN1 and CsKN2 resulted in the differential expression of numerous hormone biosynthesis and signaling genes in transgenic plants. Further evidence suggested that CsKN1 might prolong the vegetative growth period of SAM by inhibiting LEAFY. In addition, an ethylene responsive factor (CsERF) was found to bind to the CsKN1 promoter and suppresses its transcription. CsERF enhances ethylene and reactive oxygen species contents and may induce the occurrence of shoot tip abscission. Thus, we conclude that CsKN1 and CsKN2 may work cooperatively to regulate the shoot tip abscission process of sweet orange spring shoots.

CiKN1 and CiKN6 are involved in leaf development in citrus by regulating CimiR164

“…Interestingly, CiKN1 interacts with CiKN6. A recent report also showed that CiKN1 interacted with another KNOX protein (CsKN2) and was involved in the development of sweet orange spring shoots (Zeng et al., 2021). Until now, little has been determined regarding the interactions between KNOX family protein members.…”

“…Ciclev10015581m showed high homology with Arabidopsis STM among six the KNOX genes. In Arabidopsis and citrus, STM does not have a strong autonomous function in promoting leaf dissections because its activities are mainly limited to SAM and inhibited in lateral organs (Hay & Tsiantis, 2006; Zeng et al., 2021; Zhang et al., 2020). Ciclev10008269m showed high homology with KNAT3 of Arabidopsis and Medicago truncatula , and involved in the development of embryo sac and symbiotic nodule organ (Di Giacomo et al., 2017; Pagnussat et al., 2007).…”

“…Finally, Ciclev10001779m and Ciclev10001508m were selected for further analysis (Figure 2e). A previous study found that Ciclev10001508m was involved in the development of sweet orange new shoots (Zeng et al., 2021) and was named CiKN1 . Sequence alignment and phylogenetic analysis found that Ciclev10001779m has high homology with Arabidopsis KANT2/6 and was named CiKN6 (Figure S2a,b).…”

“…In addition, the leaves of CiKN1 transgenic Arabidopsis displayed a significantly higher leaf dissection index, number of teeth/leaf perimeter, and number of teeth per leaf compared with the control (Figure 3d–f). Overexpressed CiKN1 transgenic lemon was also generated (Zeng et al., 2021), and most transgenic lemon exhibited a butterfly‐like phenotype compared with the control (Figure 3g,h). However, the leaves of some transgenic lines showed a lobed‐leaf phenotype (Figures 3g and S3).…”

Citrus Genetic Transformation: An Overview of the Current Strategies and Insights on the New Emerging Technologies

“…Recently, several citrus genes that control traits of interest have been cloned and characterized as novel targets for cis and intragenesis approaches. Between them CsSAMT1 ( Salicylic acid Carboxyl Methyltransferase 1 ), which confers tolerance to HLB; CsMADS5, a fruit ripening-associated transcription factor, that positively regulates carotenoid biosynthesis in citrus; a CsMYB96 transcription factor, which enhances citrus fruit resistance against fungal pathogens; CiMADS43, a MADS-Box gene involved in citrus flowering and leaf development and CiNPR4, an NPR1-like gene that enhanced resistance of transgenic citrus plants to HLB ( Li et al, 2020 ; Khan et al, 2021 ; Lu et al, 2021 ; Peng et al, 2021b ; Zeng et al, 2021 ; Zhang et al, 2021 ; Zou et al, 2021 ).…”