Genetic Analysis Of Aboveground And Belowground Growth For The Seedling Of Populus Euphratica

Plants have evolved the dual capacity for maximizing light assimilation through stem growth and maximizing water and nutrient absorption through root growth.Previous studies have revealed the physiological and molecular mechanisms of these two organs,but the genetic basis for how stem and root interact and coordinate with one another to determine plant growth remains poorly understood.We designed a seed germination experiment using a full-sib F1 family of Populus euphratica to simultaneously monitor the growth of the radicle and the growth of the plumule throughout seedling ontogeny.We implemented three functional mapping models to identify quantitative trait loci(QTLs)that regulate main stem and taproot growth.Univariate functional mapping dissected each growth trait separately,bivariate functional mapping mapped two growth traits simultaneously,and composite functional mapping mapped the sum of main stem and taproot as a main axis.The results as follow:(1)Univariate functional mapping model located 11 QTLs related to main stem growth and 8 QTLs related to taproot growth,respectively.The genotype separation curve showed sooner or later differences.For example,ABCB8 gene related to ATPase activity promoted early(20 day)phenotypic differentiation of the taproot length phenotype.(2)Bivariate functional mapping model located 8 QTLs related to the two traits,in which GLUR,PCFS4,F-box and UBQ genes are identified as pleiotropic genes regulated the growth of both traits.This model visualized the genetic interaction between taproot length and main stem height.For example,GLUR gene involved in a variety of biological processes not only significantly affected the growth of taproot(40-75 days),but also significantly affected the growth of main stem(50-85 days).(3)Composite functional mapping model identified 7 genes significantly related to main axis growth.The model visualizes how genes affect composite traits through their component traits.For example,PCFS4 gene first regulates the growth of the main axis through the main stem length alone(0-25 days),and then simultaneously affects the growth of main stem and taproot(25-85 days).The 67th day is the node where the effect of PCFS4 gene on the growth of main stem reversely exceeds that on the growth of taproot,that is,the growth of main axis is mainly affected by the influence of PCFS4 gene on the growth of main stem.(4)The three models have different focuses and all locate the same genes BHLH98,QWRF,PCFS4 and UBQ.The results from our models provide new insight into the mechanisms of genetic control of main stem and taproot in a desert tree,and will stimulate our understanding of the relationships between above-belowground growth and tree adaptation to arid soil.