The maize heterotrimeric G protein β subunit controls shoot meristem development and immune responses

Abstract

Heterotrimeric G proteins are important transducers of receptor signaling, functioning in plants with CLAVATA receptors in controlling shoot meristem size and with pathogen-associated molecular pattern receptors in basal immunity. However, whether specific members of the heterotrimeric complex potentiate cross-talk between development and defense, and the extent to which these functions are conserved across species, have not yet been addressed. Here we used CRISPR/Cas9 to knock out the maize G protein β subunit gene (<i>Gβ</i>) and found that the mutants are lethal, differing from those in <i>Arabidopsis</i>, in which homologous mutants have normal growth and fertility. We show that lethality is caused not by a specific developmental arrest, but by autoimmunity. We used a genetic diversity screen to suppress the lethal <i>Gβ</i> phenotype and also identified a maize <i>Gβ</i> allele with weak autoimmune responses but strong development phenotypes. Using these tools, we show that <i>Gβ</i> controls meristem size in maize, acting epistatically with G protein α subunit gene (<i>Gα</i>), suggesting that <i>Gβ</i> and <i>Gα</i> function in a common signaling complex. Furthermore, we used an association study to show that natural variation in <i>Gβ</i> influences maize kernel row number, an important agronomic trait. Our results demonstrate the dual role of <i>Gβ</i> in immunity and development in a cereal crop and suggest that it functions in cross-talk between these competing signaling networks. Therefore, modification of Gβ has the potential to optimize the trade-off between growth and defense signaling to improve agronomic production.