Map-Based Cloning of zb7 Encoding an IPP and DMAPP Synthase in the MEP Pathway of Maize

Abstract

IspH is a key enzyme in the last step of the methyl-D-erythritol-4-phosphate (MEP) pathway. Loss of function of IspH can often result in complete yellow or albino phenotype in many plants. Here, we report the characterization of a recessive mutant of maize, zebra7 (zb7), showing transverse green/yellow striped leaves in young plants. The yellow bands of the mutant have decreased levels of chlorophylls and carotenoids with delayed chloroplast development. Low temperature suppressed mutant phenotype, while alternate light/dark cycle or high temperature enlarged the yellow section. Map-based cloning demonstrated that zb7 encodes the IspH protein with a mis-sense mutation in a conserved region. Transgenic silencing of Zb7 in maize resulted in complete albino plantlets that are aborted in a few weeks, confirming that Zb7 is important in the early stages of maize chloroplast development. Zb7 is constitutively expressed and its expression subject to a 16-h light/8-h dark cycle regulation. Our results suggest that the less effective or unstable IspH in zb7 mutant, together with its diurnal expression, are mechanistically accounted for the zebra phenotype. The increased IspH mRNA in the leaves of zb7 at the late development stage may explain the restoration of mutant phenotype in mature stages.

High‐efficiency genome editing using a dmc1 promoter‐controlled CRISPR/Cas9 system in maize

“…Most homozygous or bi‐allelic mutants recovered in the T1 generation showed an albino phenotype (Figure a,b). Interestingly, one plant shows a zebra phenotype, which mimics the phenotype of a mutant reported previously (Lu et al ., ; Figure c,d). From examination in detail, we found that this zb7 mutant protein has one tyrosine deletion combined with a substitution (glutamine to lysine; Figure S3b).…”

Large-scale genetic analysis of chloroplast biogenesis in maize

“…142 The mutations are recessive and are propagated by crossing heterozy- 143 gous plants. Genes that have been linked to phenotypes in the PML col- 144 lection thus far are represented by an average of~3.6 mutant alleles, 145 suggesting that the collection is nearing saturation for the chlorophyll- 146 deficiency screen that was used to assemble it. Based on allele frequen- 147 cies to date, we estimate that the chloroplast phenotypes in the collec- 148 tion result from mutations in approximately 400 different genes.…”

Over-expression of ß-carotein hydroxylase (chyB) gene affects green and albino leaves ultrastructure in Arabidopsis thaliana

“…The same phenomenon was previously observed in maltose excess 1 mutant (mex1) in A. thaliana (Michaela et al 2009). zebra7(zb7) mutant maize were found by Xiao-Min et al (2012) with decreased levels of chlorophylls and delayed chloroplast development in their yellow bands.…”