Paternally imprinted LATE-FLOWERING2 transcription factor contributes to paternal-excess interploidy hybridization barriers in wheat∞

Interploidy hybridization between hexaploid and tetraploid genotypes occurred repeatedly during genomic introgression events throughout wheat evolution,and is commonly employed in wheat breeding programs.Hexaploid wheat usually serves as maternal parent because the reciprocal cross generates progeny with severe defects and poor seed germination,but the underlying mechanism is poorly understood.Here,we performed detailed analysis of phenotypic variation in endosperm between two interploidy reciprocal crosses arising from tetraploid(Triticum durum,AABB)and hexaploid wheat(Triticum aestivum,AABBDD).In the paternal‐versus the maternal‐excess cross,the timing of endosperm cellularization was delayed and starch granule accumulation in the endosperm was repressed,causing reduced germination percentage.The expression profiles of genes involved in nutrient metabolism differed strongly between these endosperm types.Furthermore,expression patterns of parental alleles were dramatically disturbed in interploidy versus intraploidy crosses,leading to increased number of imprinted genes.The endosperm‐specific TaLFL2 showed a paternally imprinted expression pattern in interploidy crosses partially due to allele‐specific DNA methylation.Paternal TaLFL2 binds to and represses a nutrient accumulation regulator TaNAC019,leading to reduced storage protein and starch accumulation during endosperm development in paternal‐excess cross,as confirmed by interploidy crosses between tetraploid wild‐type and clustered regularly interspaced palindromic repeats(CRISPR)–CRISPR‐associated protein 9 generated hexaploid mutants.These findings reveal a contribution of genomic imprinting to paternal‐excess interploidy hybridization barriers during wheat evolution history and explains why experienced breeders preferentially exploit maternal‐excess interploidy crosses in wheat breeding programs.

The genetic and molecular basis for improving heat stress tolerance in wheat

Wheat production requires at least-2.4%increase per year rate by 2050 globally to meet food demands.However,heat stress results in serious yield loss of wheat worldwide.Correspondingly,wheat has evolved genetic basis and molecular mechanisms to protect themselves from heat-induced damage.Thus,it is very urgent to understand the underlying genetic basis and molecular mechanisms responsive to elevated temperatures to provide important strategies for heat-tolerant varieties breeding.In this review,we focused on the impact of heat stress on morphology variation at adult stage in wheat breeding programs.We also summarize the recent studies of genetic and molecular factors regulating heat tolerance,including identification of heat stress tolerance related QTLs/genes,and the regulation pathway in response to heat stress.In addition,we discuss the potential ways to improve heat tolerance by developing new technologies such as genome editing.This review of wheat responses to heat stress may shed light on the understanding heat-responsive mechanisms,although the regu-latory network of heat tolerance is still ambiguous in wheat.