Abstract
Key messageMap-based cloning of maize ms33 gene showed that ZmMs33 encodes a sn-2 glycerol-3-phosphate acyltransferase, the ortholog of rice OsGPAT3, and it is essential for male fertility in maize.Genetic male sterility has been widely studied for its biological significance and commercial value in hybrid seed production. Although many male-sterile mutants have been identified in maize (Zea mays L.), it is likely that most genes that cause male sterility are unknown. Here, we report a recessive genetic male-sterile mutant, male sterility33 (ms33), which displays small, pale yellow anthers, and complete male sterility. Using a map-based cloning approach, maize GRMZM2G070304 was identified as the ms33 gene (ZmMs33). ZmMs33 encodes a novel sn-2 glycerol-3-phosphate acyltransferase (GPAT) in maize. A functional complementation experiment showed that GRMZM2G070304 can rescue the male-sterile phenotype of the ms33-6029 mutant. GRMZM2G070304 was further confirmed to be the ms33 gene via targeted knockouts induced by the clustered regularly interspersed short palindromic repeats (CRISPR)/Cas9 system. ZmMs33 is preferentially expressed in the immature anther from the quartet to early-vacuolate microspore stages and in root tissues at the fifth leaf growth stage. Phylogenetic analysis indicated that ZmMs33 and OsGPAT3 are evolutionarily conserved for anther and pollen development in monocot species. This study reveals that the monocot-specific GPAT3 protein plays an important role in male fertility in maize, and ZmMs33 and mutants in this gene may have value in maize male-sterile line breeding and hybrid seed production.
Highlights
Male sterility refers to cases in which viable male gametes are not produced, while female gametes are fully fertile
The majority of the mutant phenotypes identified to date are controlled by recessive genes, which provide an excellent means of genetic emasculation for hybrid seed production in maize
The two ms33 mutants were crossed with the maize inbred line Chang7-2
Summary
Male sterility refers to cases in which viable male gametes (i.e., pollen) are not produced, while female gametes are fully fertile. The cloning and functional characterization of these male-sterile genes have contributed significantly to our understanding of the molecular mechanisms of anther and pollen development in maize and have provided useful genetic resources for genetic engineering of male-sterile lines for hybrid seed production. AtGPAT6 plays diverse roles in the development of pollen exine and coat, tapetum formation and stamen elongation Both Arabidopsis gpat and gpat mutants display altered endoplasmic reticulum (ER) profiles in tapetal cells as well as severely reduced pollen production and decreased pollination (Li et al 2012; Zheng et al 2003). ZmMs33 is the first GPAT gene isolated and characterized in maize, and our results will contribute to the understanding of the molecular mechanism of male sterility in maize. ZmMs33 and mutants in this gene may have value in maize male-sterile line breeding and hybrid seed production
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