Screening And Characterization Of Auxin-resistant Mutants In Rice (Oryza Sativa)

Root system is a key organ for the plant not only to absorb water and nutrients but also sense environmental stimuli and therefore its spatial distribution and size in soil will affect vegetative and reproductive growth of aerial parts.Thus,genetic dissection of molecular mechanisms of root development benefits to better understand plant developmental growth and environmental responses and guide agricultural production.Dicot roots are taproot system with a primary root and lateral roots whereas monocot roots as fibrous root system are consistent of a primary root,adventitious roots,and lateral roots.In early studies in Arabidopsis thaliana,forward genetics were used to screen a great amount of mutants defective in root development,which interfere with auxin biosynthesis and/or auxin signaling.Compared with those in Arabidopsis,very few root mutants in cereal crops were reported so far.Therefore,screening of auxin-resistant mutants in rice(Oryza sativa)root help better understanding molecular mechanisms underlying auxin regulation of root development in rice.In this study,following experiments were already carried out:(1)establishment of screening system for auxin-resistant mutants in rice;(2)screening in Huanghuazhan mutant pool mutagenized with 60Co?;(3)characterization of root system and agricultural traits;(4)establishment of F2 segregation population and screening of polymorphic primers.The results are shown as follows:1.Effects of auxin 2,4-D with different concentrations(0,0.01,0.05,0.1,0.5,1.0,and 5.0 ?M)on root elongation in wild-type Huang Huazhan were analyzed and consequently 0.5 ?M 2,4-D as an optium concentration was used to screen mutants.2.Using this screening system,188 candidates were recovered and 3 mutant lines were re-characterized as auxin-resistant mutants,which were designated with ZC-70,ZC-135,and ZC-136,respectively.ZC-136 was segregated as two independent lines ZC-136-1 and ZC-136-2.3.Analysis of root phenotypes in these mutants showed that auxin-resistant mutants ZC-70,ZC-135,and ZC-136-1 displayed normal number of adventitious roots and lateral roots and root elongation whereas those of ZC-136-2 were enhanced relative to the wild type.Characterization of agricultural traits revealed that seed setting,1000-grain weight,and yield per plant but seed length and width were reduced in the mutant ZC-70,similarly,most of yield traits were reduced in the mutants ZC-135 and ZC-136-1.By contrast,in the mutant ZC-136-2,all of yield traits but not seed width were not affected.These results suggest that ZC-70,ZC-135,and ZC-136-1 are involved in the regulation of rice yield traits,indicating a good prospect in agricultural application.4.These mutants were crossed into Nipponbare(japonica),9311(indica)and Huanghuazhan(indica)and consequently some of F2 segregation populations have been established.These F2 segregation populations showed the ratio of 3:1,indicating these mutant phenotypes are genetically controlled by a single recessive gene.Additionally,48 pairs of SSR polymorphic primers were successfully screened out by PCR using Nipponbare and Huanghuazhan genomic DNAs as PCR templates,which benefits map-based cloning in the near future.