Functional Characterization Of QKW9-a Major QTL Regulating Kernel Weight In Maize

Maize is one of most important crops in the world and the improvement of maize yield will greatly help ease the food shortage crisis.Maize yield is a very complex quantitative trait and the kernel weight is an important component of it.Dissecting the genetic mechanism of maize kernel weight and discovering new functional genes will provide targets for molecular design breeding and accelerate the breeding progress.In this study,map-based cloning was adopted to fine map a major QTL-qKW9 that regulated kernel weight,kernel length and kernel width,and functional analysis was conducted.The main results were as followings:1.Heterozygous inbred family-derived isogenic lines were developed for fine mapping of qKW9.With several rounds of recombination screening and progeny test,qKW9 was fined mapped in a region of ～20kb in B73 Ref V4.Full-length sequences of the two parental lines were obtained by BAC sequencing,and variation analysis showed that Zm00001d048451 has a 13 bp deletion in CDS region of SK which was the small-kernel parent.2.CRISPR/Cas9 system was used to conduct gene editing on Zm00001d048451 and two null alleles of Zm00001d048451 were obtained.Both mutants showed significantly decreased kernel weight and ear weight,confirming that Zm00001d048451 was the causative gene of qKW9.3.qKW9 encodes a PLS-DYW subclass PPR protein which is subcellularly located in chloroplast.Unlike most of previously reported PPR gene that affects seed development,qKW9 does not affect normal kernel development.4.RNA sequencing data showed that qKW9 significantly affected the C-to-U RNA editing of 5 chloroplast gene loci,among which the Ndh B-246 C-to-U editing was completely eliminated in the qkw9 null alleles,while the editing efficiency was close to 100% in the wild type.5.In null mutants of qKW9,the protein content and activity of NDH complex were impaired,the cyclic electron transfer rate decreased,and the photosynthetic efficiency decreased.Therefore,the cloning of qKW9 provides an interesting insight on understanding of the genetic regulation mechanism of PPR gene on maize kernel development,and this study also explores the effect of cyclic electron transfer mediated by NDH complex on photosynthesis.