The progress of the MITE mediated drought tolerance in apple

Miniature inverted-repeat transposable elements (MITEs) are widely distributed in plant genomes and regulate gene expression to affect the drought tolerance of plants. For example, the insertion of MITE in the promoter region of ZmNAC111 in maize can suppress the expression of ZmNAC111 and negatively regulate drought tolerance. Typically, RNA-directed DNA methylation (RdDM) pathway results in MITE methylation, which in turn suppresses the expression of nearby genes. However, there have also been reports suggesting that MITE methylation can affect chromatin topology or be recognized by a DNA methylation reader complex, which leading to increased gene expression. Recently, we charactered a MITE (MITE-MdRF1) inserted in the promoter of MdRFNR1 can positively regulated the drought tolerance in apple. MdRFNR1 (root-type ferredoxin-NADP⁺ oxidoreductase) plays a positive role in drought tolerance by regulating the redox system in apple, and the MITE-MdRF1 positively regulated the expression of MdRFNR1. Drought can increase the DNA methylation level of MITE-MdRF1, the methylated MITE-MdRF1 is recognized by the transcriptional anti-silencing factors MdSUVH1 and MdSUVH3, which recruit the DNAJ domain-containing proteins MdDNAJ1, MdDNAJ2, and MdDNAJ5, thereby activating MdRFNR1-1 expression under drought stress, and MdSUVH1 and MdDNAJ1 also plays a positive role in drought tolerance. These results will be useful for breeding drought-tolerant plants by genetic engineering in the future.