Genetic Mapping And Function Analysis Of Dek44 In Maize

Maize is one of important crops in the world.Kernels are not only an important reproductive organ but also the basis of yield formation.It will be helpful for improvement of maize yield and quality to understand the developmental mechanism of maize kernels.A maize kernel mutant defective kernel 44?dek44?induced by EMS was used in this study.Mature homozygous mutant kernels were lethal,small and light-colored.Kernel weight of mutant was also reduced markedly.The histological sections of kernels at different developmental stages revealed that the development of embryo and endosperm was delayed,and starch content was decreased in the dek44 mutant.Genetic analysis indicated that the phenotype of dek44 mutant was controlled by a monogenic,recessive and nuclear gene.Firstly,we placed the candidate gene on the chromosome 5 by primary mapping,and then confirmed it in an area which encompassed a physical region of 1.29 Mb.Finally,we found a C/T transition in Zm00001d014471 leading to a Ser-to-Phe substitution,and designed it as Dek44..Dek44 encodes an E subgroup PPR protein with 10 PPR motifs.Further,the RNA editing efficiency of 35 mitochondrial transcripts that encoded mitochondrial complexes was examined.The results showed that the C-to-U editing of rps13 at position 56 was completely abolished.We also found that the editing efficiency at nad9-14,nad9-92,nad9-190 and nad9-356 was dramatically decreased in dek44.In addition,we further analyzed the expression of 35 mitochondrial transcripts in wild-type and mutant kernels by RT-PCR.The results showed that the abundance of both nad1 and nad4 normal transcripts was dramatically decreased implying the splicing of genes may be affected.Then the splicing efficiency of 22mitochondrial group?introns in wild type and dek44 was compared and the splicing efficiency of nad1 intron1,nad1 intron4 and nad4 intron1 was siganificantly reduced.nad1,nad4 and nad9 encoded the subunits of complex?in mitochondria,and the defcts of them may affected the complex?.The results of examination in abundance of mitochondrial complexes by BN-PAGE?Blue Native Polyacrylamide Gel Electrophoresis?revealed that complex?and supercomplex??+?₂?were completely absent in dek44.In-gel NADH dehydrogenase assays indicated that the activities of complex?and supercomplex??+?₂?were significantly reduced in dek44.In conclusion,mutation of Dek44 affected RNA editing and intron splicing of mitochondrial transcripts,which caused mitochondrial electron transport chain impaired.The dysfunction of mitochondria might result in abnormal development of kernels.