Evaluation And Molecular Genetic Analysis Of Heterosis In A Neo-tetraploid Rice Huaduo 8

Rice polyploidy breeding can increase the probability of good genome combination and interaction,thus producing strong heterosis,which is expected to become one of the new ways of rice breeding.Autotetraploid rice is a new germplasm,have gigantic potential to increase the yield of rice and resistant to insect pest and diseases,which was developed by colchicine treatment of diploid rice.However,the fertility is generally low and difficult to apply directly.Neo-tetraploid rice,which is a new germplasm developed from autotetraploid rice,has a powerful biological and yield potential and could be used for commercial utilization.The length of panicle,as a part of rice panicle architecture,plays an important role in the yield.However,little information about long panicle associated with heterosis is available in neo-tetraploid rice.Therefore,this study focused on the evaluation and molecular genetic analysis of heterosis in neo-tetraploid rice.One is to use huaduo 8 to develop F1 with different types of tetraploid rice to systematically evaluate their heterosis;the other is to study the transcriptome of different tissues of their hybrids and parents to study the difference and function of gene expression level;the third is to use the re sequencing technology to study the whole genome of their parents and analyze the DNA variation at the genome level.The results were as follow:1.Evaluation of heterosis in a neo-tetraploid rice with large panicleIn the present study,SSR molecular marker analysis revealed Huaduo 8 harbored wide-compatibility genes for pollen and embryo sac fertility with 60% seed setting.All the hybrids generated by Huaduo 8 produced high fertility,70%,some of them passed 80%,and displayed significant high-parent and mid-parent heterosis,including number of filled grains per plant,grain yield per plant and seed setting.Among the 14 hybrid combinations,9 were developed with autotetraploid rice lines and 5 with other neo-tetraploid rice lines.All F1 hybrid generation showed long panicle type with an average panicle length of 37.61 cm.The six hybrids of them showed significant heterosis,while T49 × H8 showed the highest heterosis.In addition,compa red with their parents,the yield correlations of these hybrids were significantly improved,especially the seed setting rate,the number of seeds per plant and the yield per plant.The number of seeds per plant was more than 650,the seed setting rate was more than 77%,and the yield per plant was more than 26.50 g.2.Transcriptome analysis of the heterosisRNA-seq analysis detected a total of 4013,7050,6787 and 6195 differentially expressed genes uniquely belonging to F1 and specifically(DEGFu-sp)associated with leaf,sheath,main panicle axis and spikelet in the two hybrids,respectively.O f these DEGFu-sp,1371 common DEGFu-sp were detected in the two hybrids,KEGG analysis showed 15 pathways,including STARCH and SUCROSE METABO LISM,PHOTOSYNTHESIS,PLANT-PATHOGEN INTERACTION and CARBON FIXATION IN PHOTOSYNTHETIC ORGANISMS,etc.Among them,279 and 89 genes were related to kinase and synthetase respectively.In the kinase related genes,15 genes are annotated as receptor protein kinase,164 protein kinases,such as S-site lectin protein kinase family protein and Oswak38 Oswak receptor like protein kinase;in the synthetase genes,16 genes encode cellulose synthetase,10 genes encode ATP synthetase,and 7 genes encode phosphate synthetase.In addition,22 genes encoding NBS-LRR disease resistant protein or LRR receptor like protein kinase and 76 transcription factors were detected.Moreover,714 cloned genes were found to be differentially expressed in the two hybrids,including morphological character related genes(at least 38),physiological character related genes(at least 33),resistance or tolerance related genes(at least 66).Some important character related genes,such as grain number(gn1a)and semidwarf(sd1),were found in morphological character related genes.Four genes related to rice quality were found.Among the resistance or tolerance related genes,5 resistance genes to bacterial blight,9 resistance genes to rice blast,5 resistance genes to cold,10 resistance genes to drought and 9 resistance genes to salt were detected.In addition,the genes related to the Heterosis of diploid hybrid rice were also detected,including nal1、qgw8、osga20ox1、ghd8、gw6a、lp1、eui1、i-sd-1(t)、sd1、osga20ox2、qsd1-2、hd3a、dep1、dn1、Qpe9-1、Qngr9 and Oswrky71.In addition,2925 known QTLs were detected in the two hybrids,109 of which were related to 7 important traites,and 1393 non additive genes,766 of which were up-regulated and 627 down regulated.Eight genes related to spike were detected by q RT-PCR,and the results were all up-regulated.Re sequencing analysis showed that the DNA variation of LP(spike length gene)of H8 was different from that of many new tetraploid rice and most autotetraploid and diploid rice.The results of q RT-PCR showed that the expression of LP was up-regulated during the development of young panicle.3.Study on genome variation of ne o-tetraploid rice with large panicle germplas m huaduo 8 and its hybrid parentsH8 detected 82319 homozygous mutations related to 15146 genes compared with H1,while compared with T485,H8 detected 131112 homozygous mutations related to 24777 genes.59 specific mutations were detected in H8,including large spike gene LP、LPA1、LOC_OS01g52050 、 LOC_OS01g54270 、 LOC_OS01g54620 、 LOC_OS01g61480.In addition,compared with H1,H8 has missense variation in HD1.In H8,12 specific mutation genes related to Panicle structure of rice were also found,including osclpc2、osclpc3、lpl3、osglp8-12、sp1(osnpf4.1)、oserf71、oshsp1、oshsp17.7、spl5(sf3b3;0ssl5)、spl35 和 spl3(osedr1;osacdr1;osmapkk1).The above results showed that the neo-tetraploid rice germplasm huaduo 8 was a wide compatibility germplasm,with obvious heterosis and complex mechanism of heterosis,involving in differential expression of various types of genes.This material is expected to overcome the hybrid sterility of rice polyploid breeding.