SummaryCardiac development requires interplay between the regulation of gene expression and the assembly of functional sarcomeric proteins. We report that UNC-45b recessive loss-of-function mutations in C3H and C57BL/6 inbred mouse strains cause arrest of cardiac morphogenesis at the formation of right heart structures and failure of contractile function. Wild-type C3H and C57BL/6 embryos at the same stage, E9.5, form actively contracting right and left atria and ventricles. The known interactions of UNC-45b as a molecular chaperone are consistent with diminished accumulation of the sarcomeric myosins, but not their mRNAs, and the resulting decreased contraction of homozygous mutant embryonic hearts. The novel finding that GATA4 accumulation is similarly decreased at the protein but not mRNA levels is also consistent with the function of UNC-45b as a chaperone. The mRNAs of known downstream targets of GATA4 during secondary cardiac field development, the cardiogenic factors Hand1, Hand2 and Nkx-2.5, are also decreased, consistent with the reduced GATA4 protein accumulation. Direct binding studies show that the UNC-45b chaperone forms physical complexes with both the alpha and beta cardiac myosins and the cardiogenic transcription factor GATA4. Co-expression of UNC-45b with GATA4 led to enhanced transcription from GATA promoters in naïve cells. These novel results suggest that the heart-specific UNC-45b isoform functions as a molecular chaperone mediating contractile function of the sarcomere and gene expression in cardiac development.

Hybrid seeds are used for stimulated crop production, as they harness heterosis. The achievement of complete male-sterility in the female-parent and the restored-fertility in F1-hybrids are the major bottlenecks in the commercial hybrid seed production. Here, we report a male sterility–fertility restoration system by engineering the inmost nutritive anther wall layer tapetum of female and male parents. In the female parent, high–level, and stringent expression of Arabidopsis autophagy–related gene BECLIN1 was achieved in the tapetum, which altered the tapetal degeneration program, leading to male sterility. This works on our previously demonstrated expression cassette based on functional complementation of TATA-box mutant (TGTA) promoter and TATA-binding protein mutant3 (TBPm3), with modification by conjugating Long Hypocotyle in Far-Red1 fragment (HFR1NT131) with TBPm3 (HFR1NT131-TBPm3) to exercise regulatory control over it. In the male parent, tapetum–specific Constitutive photo-morphogenesis1 (COP1) was expressed. The F1 obtained by crossing these engineered parents showed decreased BECLIN1 expression, which was further completely abolished when COP1-mutant (COP1L105A) was used as a male parent, leading to normal tapetal development and restored fertility. The system works on COP1-HFR1 interaction and COP1–mediated degradation of TBPm3 pool (HFR1NT131-TBPm3). The system can be deployed for hybrid seed production in agricultural crops.

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