Multiple Alleles Encoding Atypical NLRs with Unique Central Tandem Repeats in Rice Confer Resistance to Xanthomonas oryzae pv. oryzae

Plants have developed various mechanisms for avoiding pathogen invasion,including resistance(R)genes.Most R genes encode nucleotide-binding domain and leucine-rich repeat containing proteins(NLRs).Here,we report the isolation of three new bacterial blight R genes in rice,Xa1-2,Xa14,and Xa31(t),which were allelic to Xa1 and encoded atypical NLRs with unique central tandem repeats(CTRs).We also found that Xa31(t)was the same gene as Xa1-2.Although Xa1-2 and Xa14 conferred different resistance spectra,their performance could be attenuated by iTALEs,as has previously been reported for Xa1.XA1,XA1-2,XA14,and non-resistant RGAF differed mainly in the substructure of the leucine-rich repeat domain.They all contained unique CTRs and belonged to the CTR-NLRs,which existed only in Gramineae.We also found that interactions among these genes led to differing resistance performance.In conclusion,our results uncover a unique locus in rice consisting of at least three multiple alleles(Xa1,Xa1-2,and Xa14)that encode CTRNLRs and confer resistance to Xanthomonas oryzae pv.oryzae(Xoo).

Studies of Multi-Allelic Polymorphism of Dominant Dwarfing Genes in Wheat

Dwarfing breeding of wheat in the world is confined to the exploitation of recessive dwarfing sources. None of the dominant dwarfing sources discovered in common wheat (Triticum aestivum L.) has found wide exploitation in wheat breeding due to the extreme dwarfness of their plants (2055 cm). We found in our work that some stable mutant lines with their plant height enhanced to different extents could be obtained in large populations derived from the stock seeds of the dominant dwarfing sources Aibian1 carrying Rht10 on 4DS and being 2055 cm tall and Aisu2 carrying Rht3 on 4BS and being 55 cm tall, or from their descendants of induced mutation treatments, or from the segregating descendants of their crosses with mid- or tall-statured genotypes. Subsequently, we studied these mutation-derived lines differing in plant height with near isogenic lines and observed that the character of their enhanced plant height bred true, each carrying a semi-dominant dwarfing gene for a definite height and that as the plant height of the mutation-derived lines increased, the yield-contributing characters of their near isogenic lines were significantly improved. When test crosses with marker genes and physiological and biochemical genetic marker tests were performed to re-localize the semi-dominant dwarfing genes carried by the mutation-derived lines, it was confirmed that they shared common loci with Rht10 and Rht3 and that they were all mutation-derived multiple alleles. It is thus speculated that dominant dwarfing genes are of 'multi-allelic polymorphism'. In other words, dominant dwarfing genes, which are ultra-dwarfing, are liable to develop by mutation into a group of multiple alleles with plant height enhanced to different extents and some may have a height close to the ideal plant height for wheat breeding. Therefore, these results offer a fundamentally new approach for the exploitation of dominant dwarfing sources in wheat breeding.