Novel genome editing approaches to manipulate apical meristem activity for crop yield

Meristem function underlies organogenesis and yield potential in crop species, and its regulation depends on the crosstalk of genetic and hormonal networks that balance stem-cell niche maintenance and differentiation. During the shoot apical meristem (SAM) transition, developmental reprogramming shifts the meristem from a vegetative to a reproductive state, referred to as inflorescence meristem (IM). Major regulatory events in this transition include the cytokinin-gibberellin crosstalk, that regulate the expression of the CLAVATA/WUSCHEL (CLV/WUS) negative feedback loop and key transcription factor families like KNOTTED-LIKE HOMEOBOX (KNOX) and SHOOT MERISTEMLESS (STM). Despite the basic principles of apical meristem differentiation are well-described nowadays, major phenotypic bottlenecks were reached in major staple crops during the artificial selection process, known as domestication, leading to a final reduction in total crop yield. This review aims to describe the key processes and genes that play a role in this transition and how they can be artificially targeted to overcome these limitations. Major bioengineering approaches are covered, ranging from classical random mutagenesis with chemicals like ethyl methanesulfonate (EMS) to targeted genome editing using diverse Clustered Regularly Interspaced Short Palindromic Repeats and CRISPR-associated proteins (CRISPR/Cas) systems. Finally, emerging strategies such as epibreeding are considered as promising tools to achieve precise, reversible modulation of meristem activity and to unlock new routes for crop yield enhancement.