Genetic bases of source-,sink-,and yield-related traits revealed by genome-wide association study in Xian rice

The source-sink relationship determines the ultimate grain yield.We investigated the genetic basis of the relationship between source and sink and yield potential in rice.In two environments,we identified quantitative trait loci(QTL)associated with sink capacity(total spikelet number per panicle and thousand-grain weight),source leaf(flag leaf length,flag leaf width and flag leaf area),source-sink relationship(total spikelet number to flag leaf area ratio)and yield-related traits(filled grain number per panicle,panicle number per plant,grain yield per plant,biomass per plant,and harvest index)by genome-wide association analysis using 272 Xian(indica)accessions.The panel showed substantial variation for all traits in the two environments and revealed complex phenotypic correlations.A total of 70 QTL influencing the 11 traits were identified using 469,377 high-quality SNP markers.Five QTL were detected consistently in four chromosomal regions in both environments.Five QTL clusters simultaneously affected source,sink,source–sink relationship,and grain yield traits,probably explaining the genetic basis of significant correlations of grain yield with source and sink traits.We selected 24 candidate genes in the four consistent QTL regions by identifying linkage disequilibrium(LD)blocks associated with significant SNPs and performing haplotype analysis.The genes included one cloned gene(NOG1)and three newly identified QTL(qHI6,qTGW7,and qFLA8).These results provide a theoretical basis for high-yield rice breeding by increasing and balancing source–sink relationships using marker-assisted selection.

Physiological and molecular studies of staygreen caused by pod removal and seed injury in soybean

Leaves provide substances and signals for pod and seed development in soybean.However,the regulatory feedbacks of pod and seed to leaf development remain unclear.We investigated the effects of pod and seed on leaf senescence by conducting pod removal and seed injury experiments.Pod removal and seed injury delayed leaf senescence and caused the staygreen phenotype of leaves.There were dosage effects of pod number on the extent of staygreen in depodded plants.The concentrations of chlorophyll(SPAD value,an index of relative chlorophyll content),soluble protein,and soluble sugar in the leaves of depodded plants were higher than those of intact plants.During seed development,the content of IAA decreased,while that of ABA increased.This trend was more pronounced in intact than in depodded and seed-injured plants.The GA3/ABA ratio decreased gradually in all treatments.The content of GA3 was relatively stable and was higher in intact than in depodded plants.The expression levels of four senescence-related genes,Gm SARK,Gm SGR1,Gm CYN1,and Gm NAC,declined in depodded or seed-injured treatments and were positively correlated with the number of leaves retained on plants.Gm FT2 a,the major flowering-promoting gene,was expressed at a higher level while E1,a key flowering inhibitory gene,was expressed at a lower level in depodded than in intact plants.We propose that the pod or seed can regulate leaf development.When the seed is aborted owing to disease infection or pest attack,the leaves stay green because of the absence of the seed signals for senescence.