The availability of the B73 inbred reference genome sets the stage for high-throughput functional characterization of maize genes on a whole-genome scale. Among the 39 324 protein-coding genes predicted, the vast majority are untapped due to the lack of suitable high-throughput reverse genetic resources. We have generated a gene-indexed maize mutant collection through ethyl methanesulfonate mutagenesis and detected the mutations by combining exome capture and next-generation sequencing. A total of 1086 mutated M plants were sequenced, and 195 268 CG>TA-type point mutations, including stop gain/loss, missplice, start gain/loss, and various non-synonymous protein mutations as well as 4610 InDel mutations, were identified. These mutations were distributed on 32 069 genes, representing 82% of the predicted protein-coding genes in the maize genome. We detected an average of 180 mutations per mutant line and 6.1 mutations per gene. As many as 27 214 mutations of start codons, stop codons, or missplice sites were identified in 14 101 genes, among which 6232 individual genes harbored more than two such mutations. Application of this mutant collection is exemplified by the identification of the ent-kaurene synthase gene, which encodes a key enzyme in the gibberellin biosynthesis pathway. This gene-indexed genome-wide mutation collection provides an important resource for functional analysis of maize genes and may bring desirable allelic variants for genetic breeding in maize.
BackgroundZinc (Zn) and iron (Fe) are essential micronutrients for plant growth and development, their deficiency or excess severely impaired physiological and biochemical reactions of plants. Therefore, a tightly controlled zinc and iron uptake and homeostasis network has been evolved in plants. The Zinc-regulated transporters, Iron-regulated transporter-like Proteins (ZIP) are capable of uptaking and transporting divalent metal ion and are suggested to play critical roles in balancing metal uptake and homeostasis, though a detailed analysis of ZIP gene family in maize is still lacking.ResultsNine ZIP-coding genes were identified in maize genome. It was revealed that the ZmZIP proteins share a conserved transmembrane domain and a variable region between TM-3 and TM-4. Transiently expression in onion epidermal cells revealed that all ZmZIP proteins were localized to the endoplasmic reticulum and plasma membrane. The yeast complementation analysis was performed to test the Zn or Fe transporter activity of ZmZIP proteins. Expression analysis showed that the ZmIRT1 transcripts were dramatically induced in response to Zn- and Fe-deficiency, though the expression profiles of other ZmZIP changed variously. The expression patterns of ZmZIP genes were observed in different stages of embryo and endosperm development. The accumulations of ZmIRT1 and ZmZIP6 were increased in the late developmental stages of embryo, while ZmZIP4 was up-regulated during the early development of embryo. In addition, the expression of ZmZIP5 was dramatically induced associated with middle stage development of embryo and endosperm.ConclusionsThese results suggest that ZmZIP genes encode functional Zn or Fe transporters that may be responsible for the uptake, translocation, detoxification and storage of divalent metal ion in plant cells. The various expression patterns of ZmZIP genes in embryo and endosperm indicates that they may be essential for ion translocation and storage during differential stages of embryo and endosperm development. The present study provides new insights into the evolutionary relationship and putative functional divergence of the ZmZIP gene family during the growth and development of maize.
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