Applying conventional and cell-type-specific CRISPR/Cas9 genome editing in legume plants

The advent of genome editing technologies, particularly CRISPR/Cas9, has significantly advanced the generation of legume mutants for reverse genetic studies and understanding the mechanics of the rhizobial symbiosis. The legume–rhizobia symbiosis is crucial for sustainable agriculture, enhancing nitrogen fixation and improving soil fertility. Numerous genes with a symbiosis-specific expression have been identified, sometimes exclusively expressed in cells forming infection threads or in nitrogen-fixing nodule cells. Typically, mutations in these genes do not affect plant growth. However, in some instances, germline homozygous mutations can be lethal or result in complex pleiotropic phenotypes that are challenging to interpret. To address this issue, a rhizobia-inducible and cell-type-specific CRISPR/Cas9 strategy was developed to knock-out genes in specific legume transgenic root tissues. In this review, we discuss recent advancements in legume genome editing, highlighting the cell-type-specific CRISPR system and its crucial applications in symbiotic nitrogen fixation and beyond.