Discovery Of Soybean Cyvst Nematode-resistance Soybean Germplasms And Functional Genes

As a major source of plant proteins,soybean is an important oil,grain and forage crop in China.With increasing demand,which is now relied on import,the soybean industry in China is facing serious challenges.In recent years,with limited crop rotations,soybean diseases are becoming increasingly serious.Soybean cyst nematode?SCN?is the most important soybean pest.Utilization of SCN-resistant soybean cultivars is the major approach for controlling SCN.However,there are multiple races of SCN and increased use of a single resistant cultivar can lead to gradual or even complete breakdown of resistance.To address these issues,this study has analyzed the SCN races in soil samples collected from soybean-cultivated fields.The study has also analyzed the two new germplasm lines that are highly resistance to SCN and identified resistance-linked molecular makers.A legume-specific protein family has also been analyzed for their effects on soybean SCN resistance.The major results from the study include:1.Using the standard soybean lines for SCN4 race diagnosis,we have analyzed the SCN samples collected from the experimental station of Chinese Academy of Agricultural Science in Longfang,Hebei Province.Our analysis indicated that the SCN in these soil samples belongs predominantly to Race 4,with a small percentage to other races.2.We have discovered two new soybean lines?P1437654 and P1438489B?that are highly SCN4 resistance and identified linked molecular markers.Using the two high SCN-resistant lines and the highly susceptible Williams 82 cultivar,we have identified 73 polymorphic SSR markers,which are distributed on all 20 soybean chromosomes.Among the 73 polymorpic markers,18 are linked with the SCN4 resistance in PI43765 and PI438489B.Those linked with the SCN4 reisistance from PI437654 include satt050?sattl74?satt619?AW132402?satt020?AW781285?satt005?satt038?satt142?sat₁70?satt63 and satt358;those linked with the SCN resistance in PI438489B include satt050?satt619?AW132402?satt197?satt396?satt578?satt399?satt343?Sat₁70?satt481?and satt336.These identified SSR marks are co-dominant,reliable and reproducible.By investigating the segregating F2 population from the PI438489B x Williams82 cross,the ratio of SCN-resistant progeny to the susceptible progeny was close to 3,suggesting that the resistance is conferred by a single dominant gene.3.We have analyzed the effects of a legume-specific protein family on soybean SCN4 resistance.The members of the protein family all share a unique Golgi-targeting transmembrane?TM?domain at their N-terminus,with a majority of members also containing a WRKY or Exo70 domain.Using transgenic soybean hairy roots,we discovered that overexpression of GmExo70J7 and GmExo70J12 resulted in significant increased SCN resistance.On the other hand,overexpression of a truncated GmWRP1 and another family member containing only the TM domain significantly reduced SCN resistance.These results indicate that this legume-specific protein family is involved in the interactions between soybean host and SCN.