DEK43 Regulates Maize Kernel Development By Affecting Mitochondrial Function

As the main storage organ,the development of kernels is important for maize yield.The study on the mechanism of maize kernel development will be helpful for the improvement of maize kernel yield and quality.Mitochondria are the energy factory for plant cells and the main site for aerobic respiration,the electron transport chain is the core of mitochondrial production capacity.The NADH dehydrogenase 4?nad4?gene encodes mitochondrial respiratory chain complex I subunit IV.Plant mitochondrial genes contain group II introns that must be spliced before translation.PPR proteins are nuclear encoded regulators involved in organelle gene expression,includes RNA editing,intron splicing,transcription,and stability.P type PPR proteins are mainly involved in the splicing process of organelle mRNA.In this study,a maize defective kernel mutant was identified and designed defective kernel 43?dek43?.The dek43 mutant has small,lethal,light-colored kernel.The 100-grain weight of mutant kernels was also significantly reduced.The results of histological sections of the kernels at different stages showed that the development of embryo and endosperm in dek43 mutant is obvious lagging,and the accumulation of starch in the endosperm decreased.We identified the mutant gene through Map-based cloning approache and 938 mutant seeds were screened in the F₂ segregation population,The gene was located in a range of about 900 Kb by 12 molecular markers.There are 28 genes in this region,Zm00001d021053was identified as the target gene by sequencing and named Dek43.it was found that the gene co-located in nucleus and mitochondria.Sequence analysis showed that Dek43 encodes a P-type Pentatricopeptide repeat?PPR?protein that was mainly involved in the splicing process of organelle mRNA in higher plants.Then the splicing efficiency of the 22mitochondrial group II introns was compared in wild type and dek43 mutant.The result revealed that the splicing efficiency of the first and the third introns of the gene nad4 was dramatically reduced.Because nad4 gene codes mitochondrial respiratory chain complex I subunit 4,so we further examined assembly and steady-state levels of the respiratory complexes.The results of blue native polyacrylamide gel electrophoresis showed that the bands corresponding to complex I and supercomplex I+III₂ were significantly reduced in dek43.In-gel NADH dehydrogenase assays indicated that the activities of complex I and supercomplex I+III₂ were both significantly reduced in dek43.The RNA-seq analysis revealed that the expression of mitochondrial related genes in dek43 were up-regulated and several starch biosynthesis related genes were down-regulated.Taken together,our data suggested that Dek43 played an important role in maintaining the normal function of mitochondria and the normal development of maize kernel.