Find in Library

The mitogen-activated protein kinase (MAPK) signaling cascade is a widely existing signal transduction system in eukaryotes, and plays an important role in the signal transduction processes of plant cells in response to environmental stress. In this study, we screened <i>MdMKK9</i>, a gene in the MAPK family. This gene is directly related to changes in anthocyanin synthesis in the ‘Daihong’ variety of red-fleshed apple (<i>Malus sieversii f neidzwetzkyana</i> (Dieck) Langenf). <i>MdMKK9</i> expression was up-regulated in ‘Daihong’ tissue culture seedlings cultured at low levels of nitrogen. This change in gene expression up-regulated the expression of genes related to anthocyanin synthesis and nitrogen transport, thus promoting anthocyanin synthesis and causing the tissue culture seedlings to appear red in color. To elucidate the function of <i>MdMKK9</i>, we used the CRISPR/Cas9 system to construct a gene editing vector for <i>MdMKK9</i> and successfully introduced it into the calli of the ‘Orin’ apple. The <i>MdMKK9</i> deletion mutants (MUT) calli could not respond to the low level of nitrogen signal, the expression level of anthocyanin synthesis-related genes was down-regulated, and the anthocyanin content was lower than that of the wild type (WT). In contrast, the <i>MdMKK9</i>-overexpressed calli up-regulated the expression level of anthocyanin synthesis-related genes and increased anthocyanin content, and appeared red in conditions of low level of nitrogen or nitrogen deficiency. These results show that <i>MdMKK9</i> plays a role in the adaptation of red-fleshed apple to low levels of nitrogen by regulating the nitrogen status and anthocyanin accumulation.