The transcription factors ZmFAMA and ZmSCRM2 form a heterodimeric complex to regulate stomatal development in maize

Stomata, specialized structures on the plant epidermis, are crucial for regulating gas and water exchange, thereby influencing global carbon cycles. This study investigates the role of the basic helix-loop-helix (bHLH) transcription factors ZmFAMA and ZmSCRM2 in stomatal development in maize (Zea mays), focusing on their involvement in guard cell morphogenesis. Screening of a mutagenized maize seed population identified a mutant (zmfama-1) which exhibits abnormal guard cell morphology characterized by rod-like structures instead of the typical dumbbell shape, while maintaining wild-type stomatal density. Whole-genome sequencing revealed a mutation in the 5'-untranslated region of ZmFAMA leading to an out-of-frame translation, and phenotypic analysis confirmed its pivotal role in guard cell development. Additionally, ZmSCRM2 was found to interact with ZmFAMA, forming heterodimers that regulate gene expression during stomatal morphogenesis. RNA-seq analysis revealed significant changes in gene expression profiles in zmfama and zmscrm2 mutants, particularly in genes associated with photosynthesis and stomatal movement. Our findings suggest that while ZmFAMA and ZmSCRM2 share conserved functions with their Arabidopsis counterparts, they also have specialized roles defining the unique stomatal architecture in grasses. This work enhances our understanding of the genetic and molecular mechanisms governing stomatal development, providing avenues for crop improvement strategies in response to environmental stress.