A novel hybrid seed production technology based on a unilateral cross-incompatibility gene in maize

Hybrid seed production technology(SPT)using genic recessive male sterility is of great importance in maize breeding.Here,we report a novel SPT based on a maize unilateral cross-incompatibility gene Zm Ga1F with an extremely low transgene transmission rate(TTR).Proper pollen-specific Zm Ga1F expression severely inhibits pollen tube growth leading to no fertilization.The maintainer line harbors a transgene cassette in an ipe1 male sterile background containing IPE1 to restore ipe1 male fertility,Zm Ga1F to prevent transgenic pollen escape,the red fluorescence protein encoding gene Ds Red2 for the separation of male sterile and fertile seeds,and the herbicide-resistant gene Bar for transgenic plant selection.When the maintainer line is selfed,gametes of ipe1/transgene and ipe1/-genotypes are produced,and pollen of the ipe1/transgene genotype is not able to fertilize female gametes due to pollen tube growth inhibition by Zm Ga1F.Subsequently,seeds of ipe1/ipe1 and ipe1/transgene genotypes are produced at a 1:1 ratio and could be separated easily by fluorescence-based seed sorting.Not a single seed emitting fluorescence is detected in more than 200,000 seeds examined demonstrating that the pollen-tube-inhibition(PTI)-based TTR is lower than what has been reported for similar technologies to date.This PTI-based SPT shows promising potential for future maize hybrid seed production.

ORF355 confers enhanced salinity stress adaptability to S-type cytoplasmic male sterility maize by modulating the mitochondrial metabolic homeostasis

Moderate stimuli in mitochondria improve wideranging stress adaptability in animals, but whether mitochondria play similar roles in plants is largely unknown. Here, we report the enhanced stress adaptability of S-type cytoplasmic male sterility(CMS-S) maize and its association with mild expression of sterilizing gene ORF355. A CMS-S maize line exhibited superior growth potential and higher yield than those of the near-isogenic N-type line in saline fields. Moderate expression of ORF355 induced the accumulation of reactive oxygen species and activated the cellular antioxidative defense system. This adaptive response was mediated by elevation of the nicotinamide adenine dinucleotide concentration and associated metabolic homeostasis. Metabolome analysis revealed broad metabolic changes in CMS-S lines, even in the absence of salinity stress. Metabolic products associated with amino acid metabolism and galactose metabolism were substantially changed, which underpinned the alteration of the antioxidative defense system in CMS-S plants. The results reveal the ORF355-mediated superior stress adaptability in CMS-S maize and might provide an important route to developing salt-tolerant maize varieties.

A single silk-and multiple pollen-expressed PMEs at the Ga1 locus modulate maize unilateral cross-incompatibility

The Gametophyte factor1(Ga1) locus in maize confers unilateral cross-incompatibility(UCI), and it is controlled by both pollen and silk-specific determinants. Although the Ga1 locus has been reported for more than a century and is widely utilized in maize breeding programs, only the pollen-specific ZmGa1P has been shown to function as a male determinant;thus, the genomic structure of the Ga1 locus and all the determinants that control UCI at this locus have not yet been fully characterized.Here, we used map-based cloning to confirm the determinants of UCI at the Ga1 locus and maize pan-genome sequence data to characterize the genomic structure of the Ga1 locus. The Ga1 locus comprises one silk-expressed pectin methylesterase gene(PME, ZmGa1F) and eight pollenexpressed PMEs(ZmGa1P and ZmGa1PL1-7).Knockout of ZmGa1F in Ga1/Ga1 lines leads to the complete loss of the female barrier function. The expression of individual ZmGa1PL genes in a ga1/ga1 background endows ga1 pollen with the ability to overcome the female barrier of the Ga1 locus. These findings, combined with genomic data and genetic analyses, indicate that the Ga1 locus is modulated by a single female determinant and multiple male determinants, which are tightly linked.The results of this study provide valuable insights into the genomic structure of the Ga2 and Tcb1 loci and will aid applications of these loci in maize breeding programs.

Generation of thermosensitive male-sterile maize by targeted knockout of the ZmTMS5 gene

Maize（Zea mays L.）is one of the most important cereal crops,with a global production of 1.02 billion tons in 2013（Baldaufa et al.,2016）.Heterosis is widely used to increase the productivity of maize,and the first commercial hybrid maize was introduced in the 1930s（Duvick,2001）.

Activation of Mitochondrial orf355 Gene Expression by a Nuclear-Encoded DREB Transcription Factor Causes Cytoplasmic Male Sterility in Maize

Coordination between mitochondria and the nucleus is crucial for fertility determination in plants with cytoplasmic male sterility(CMS).Using yeast one-hybrid screening,we identified a transcription factor,ZmDREB1.7,that is highly expressed in sterile microspores at the large vacuole stage and activates the expression of mitochondria-encoded CMS gene orf355.Δpro,a weak allele of ZmDREB1.7 with the loss of a key unfolded protein response(UPR)motif in the promoter,partially restores male fertility of CMS-S maize.ZmDREB1.7 expression increases rapidly in response to antimycin A treatment,but this response is attenuated in theΔpro allele.Furthermore,we found that expression of orf355 in mitochondria activates mitochondrial retrograde signaling,which in turn induces ZmDREB1.7 expression.Taken together,these findings demonstrate that positive-feedback transcriptional regulation between a nuclear regulator and a mitochondrial CMS gene determines male sterility in maize,providing new insights into nucleus-mitochondria communication in plants.