Abstract
Maize is monecious, with separate male and female inflorescences. Maize flowers are initially bisexual but achieve separate sexual identities through organ arrest. Loss-of-function mutants in the jasmonic acid (JA) pathway have only female flowers due to failure to abort silks in the tassel. Tasselseed5 (Ts5) shares this phenotype but is dominant. Positional cloning and transcriptomics of tassels identified an ectopically expressed gene in the CYP94B subfamily, Ts5 (ZmCYP94B1). CYP94B enzymes are wound inducible and inactivate bioactive jasmonoyl-L-isoleucine (JA-Ile). Consistent with this result, tassels and wounded leaves of Ts5 mutants displayed lower JA and JA-lle precursors and higher 12OH-JA-lle product than the wild type. Furthermore, many wounding and jasmonate pathway genes were differentially expressed in Ts5 tassels. We propose that the Ts5 phenotype results from the interruption of JA signaling during sexual differentiation via the upregulation of ZmCYP94B1 and that its proper expression maintains maize monoecy.
COMMUNICATIONS BIOLOGY | (2019) 2:114 | https://doi.org/10.1038/s42003-019-0354-1 | www.nature.com/commsbio
liguleless narrow1 encodes a plasma membrane-localized receptor-like kinase required for normal maize development. The semi-dominant Lgn-R mutation lacks kinase activity and severity depends on inbred background. We created near isogenic lines and assayed the phenotype in multiple environments. Lgn-R plants that carry the B73 version of Sympathy for the ligule die in hot conditions but those with the Mo17 version (Sol-M) survive and are taller at cool temperatures. To identify Sol, we used recombinant mapping and analyzed the Lgn-R phenotype in additional inbreds. We identified sequence variations in GRMZM2G075262 that segregate with the Lgn-R phenotypes. Gene expression is high in Lgn-R B73 but not with one copy of Sol-M. An EMS mutation confirmed SOL as a homolog of Arabidopsis ENHANCED DISEASE RESISTANCE4 (EDR4). SOL, like EDR4, is induced in response to pathogen associated molecular patterns. Integrated transcriptomic and phosphoproteomic analyses suggest that Lgn-R plants constitutively activate a MAP kinase signaling cascade that induces temperature-sensitive immune responses. We propose that the severe Lgn-R phenotypes result from constitutive defense induction and that SOL functions in repressing this response in Mo17 but not B73. Identification of LGN and SOL provide insight into the integration of developmental control and immunity.
Plant Cell Advance Publication. Published on June 19, 2019, doi:10.1105/tpc.18.00840