Indentification And Genetic Mapping Of A Sterile And Malformed Spike 1 Gene In Commen Wheat

The differentiation and development of spike is an important phase of wheat growth,which affects final grain yield and quality.Therefore,to explore the genetic mechanism of spike development is of great significance for genetic improvement of yield traits.In this study,a sterile and malformed spike mutant was obtained from the breeding material and defined as sms1.Morphological and histological observation of the mutants was carried out.The gene was fine-mapped,combined with comparative genomics and transcriptomics analysis to clone and understand the genetic mechanism of sms1 gene.The main results of this study are as follows:1.Compared with the wild type,the mutant sms1 showed delayed heading,After the heading,the mutant sms1 showed the plants height slightly lower,the glume got longer,lower number of spikelets and increased spacing between spikelets,thinner filaments,shriveled anthers and indehiscent anthers and atrophic pistil stigma.A large number of reciprocal crosses were carried out between the mutant and other varieties,the majority of them did not produce hybrid seeds.It was verified that the pollen of mutant sms1 were almost completely lost fertility with 1 % I2-KI solution.The results showed that the sms1 mutant was a male and female sterile mutant.2.The dynamic observation of the spike differentiation process using the stereomicroscope.It was showed that the mutant had seen the phenotypic variation from the differentiation stage of the spikelet primordium.The main reason for the large spikelet spacing may be related to the increase of cell volume between spikelets.The paraffin sections of anther showed that the majority of microspores in the drug chamber began to degrade,and the deformities were irregular.SEM showed that the density of granular on mutant pollen surface significantly diminished,which was a single type of particles and arranged sparse,the hole ring uplift of pollen germination hole was not obvious,hole cover depression.The inner wall of mutant anthers had less granule and the arrangement was sparse,which explained the mutant sms1 male sterility.The cause of the mutant sms1 female infertility was that the stigma feathers are sparse,have little feathers and short length,the ability to accept pollen is deteriorated.3.The segregation ratio of wild type and mutant plants fit the ratio of 3: 1,and ratio of isolation strains and not isolation were 2:1 by chi square test,which showed that the mutant trait was controlled by a pair of recessive genes.Due to the high degree of sterility of the mutant,the mutant gene sms1 can only be maintained by heterozygote.We used the heterozygote to hybridize with the normal wheat cultivars,and we obtained a F2 isolate containing 158 individuals.The SSR markers were screened by means of bulked segregant analysis,the gene sms1 was preliminary located on the chromosome 6B,with the genetic distance of 2.00 c M and 26.30 c M to the markers Xwmc539 and Xgwm219.Expand the population,and the SSR markers were developed from the prepublication data of IWGSC Whole Genome Assembly Chinese Spring v0.4 pseudo molecules sequence.The sms1 gene was located between SSR178 and SSR231,with a genetic distance of 0.22 c M and a physical distance of about 3.4 Mb.4.By comparing genomics,it was found that all gene orders in the sms1 region between wheat and barley,rice,sorghum and Brachypodium are completely consistent,especially with barley.So,we used the barley genome to annotate the genes in the sms1 region.According to the annotation of homologs in barley,17 candidate genes were predicted in about 3.4 Mb region of wheat,Out of 7 genes with possible differential expressed in two NIL lines,and 5 genes had annotated information.Gene3 is a transcription elongation factor SPT5-like protein,a plant-specific RNA polymerase elongation factor member of the nuclear SPT5 family.In this study,the expression of SPT5-like gene was much higher than that in wild type,and the phenotype of delayed heading,shrinking spikelet number and the dysfunction of reproductive organ was found in mutant.It was highly consistent with the previous study that the decrease of SPT16 protein could result in early flowering,many flowers and abnormal reproductive organs.It is conceivable that SPT5-like probably is the candidate gene of sms1.