HvSL1 and HvMADS16 promote stamen identity to restrict multiple ovary formation in barley

A novel type of malformed floral organs mutant in barley was conferred by loss-of-function mutations of the MADS-box gene HvAGL6

The advanced model of floral morphogenesis is based largely on data from Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa), but this process is less well understood in the Triticeae. Here, we investigated a sterile barley (Hordeum vulgare) mutant with malformed floral organs (designated mfo1), of which the paleae, lodicules, and stamens in each floret were all converted into lemma-like organs, and the ovary was abnormally shaped. Combining bulked-segregant analysis, whole-genome resequencing, and TILLING approaches, the mfo1 mutant was attributed to loss-of-function mutations in the MADS-box transcription factor gene HvAGL6, a key regulator in the ABCDE floral morphogenesis model. Through transcriptomic analysis between young inflorescences of wild-type and mfo1 plants, 380 genes were identified as differentially expressed, most of which function in DNA binding, protein dimerization, cell differentiation, or meristem determinacy. Regulatory pathway enrichment showed HvAGL6 associates with transcriptional abundance of many MADS-box genes, including the B-class gene HvMADS4. Mutants with deficiency in HvMADS4 exhibited the conversion of stamens into supernumerary pistils, producing multiple ovaries resembling the completely sterile multiple ovaries 3.h (mov3.h) mutant. These findings demonstrate that the regulatory model of floral morphogenesis is conserved across plant species and provides insights into the interactions between HvAGL6 and other MADS-box regulators.

MADS8 is indispensable for female reproductive development at high ambient temperatures in cereal crops

Temperature is a major factor that regulates plant growth and phenotypic diversity. To ensure reproductive success at a range of temperatures, plants must maintain developmental stability of their sexual organs when exposed to temperature fluctuations. However, the mechanisms integrating plant floral organ development and temperature responses are largely unknown. Here, we generated barley and rice loss-of-function mutants in the SEPALLATA-like MADS-box gene MADS8. The mutants in both species form multiple carpels that lack ovules at high ambient temperatures. Tissue-specific markers revealed that HvMADS8 is required to maintain floral meristem determinacy and ovule initiation at high temperatures, and transcriptome analyses confirmed that temperature-dependent differentially expressed genes in Hvmads8 mutants predominantly associate with floral organ and meristem regulation. HvMADS8 temperature-responsive activity relies on increased binding to promoters of downstream targets, as revealed by a cleavage under targets and tagmentation (CUT&Tag) analysis. We also demonstrate that HvMADS8 directly binds to 2 orthologs of D-class floral homeotic genes to activate their expression. Overall, our findings revealed a new, conserved role for MADS8 in maintaining pistil number and ovule initiation in cereal crops, extending the known function of plant MADS-box proteins in floral organ regulation.