A PECTIN METHYLESTERASE gene at the maize Ga1 locus confers male function in unilateral cross-incompatibility

Zhaogui Zhang,Senlin Xiao,Mingming Wang,Xu Liu,Dongmei Zhang,Juan Liu,Li Zhao,Hang Wang,Huairen Zhang,Yihua Zhou,Yongbiao Xue,Darun Cai,Yu’E Zhang,Lanjun Zhang,Zhibin Chen,Yanqing Huo,Jie Liu,Baocai Zhang,Huabang Chen

doi:10.1038/s41467-018-06139-8

Abstract

Unilateral cross-incompatibility (UCI) is a unidirectional inter/intra-population reproductive barrier when both parents are self-compatible. Maize Gametophyte factor1 (Ga1) is an intraspecific UCI system and has been utilized in breeding. However, the mechanism underlying maize UCI specificity has remained mysterious for decades. Here, we report the cloning of ZmGa1P, a pollen-expressed PECTIN METHYLESTERASE (PME) gene at the Ga1 locus that can confer the male function in the maize UCI system. Homozygous transgenic plants expressing ZmGa1P in a ga1 background can fertilize Ga1-S plants and can be fertilized by pollen of ga1 plants. ZmGa1P protein is predominantly localized to the apex of growing pollen tubes and may interact with another pollen-specific PME protein, ZmPME10-1, to maintain the state of pectin methylesterification required for pollen tube growth in Ga1-S silks. Our study discloses a PME-mediated UCI mechanism and provides a tool to manipulate hybrid breeding.

Highlights

Unilateral cross-incompatibility (UCI) is a unidirectional inter/intra-population reproductive barrier when both parents are self-compatible
To visualize the in vivo difference in the degree of methyl esterification (DM) at the pollen-tube apexes, we developed near isogenic lines JKNGa1-S and JKNga[1] that differ at the Gametophyte factor1 (Ga1) locus and compared the DM of the pollen tube walls between selfing and reciprocal crosses
UCI may provide a selective biological barrier to manipulate a Discussion Incompatibility in flowering plants has a great impact on species evolution and resource exploitation

Summary

Introduction

Unilateral cross-incompatibility (UCI) is a unidirectional inter/intra-population reproductive barrier when both parents are self-compatible. We report the cloning of ZmGa1P, a pollen-expressed PECTIN METHYLESTERASE (PME) gene at the Ga1 locus that can confer the male function in the maize UCI system. UCI is a postpollination reproductive barrier that unidirectionally prevents hybridization when male and female parents are self-compatible[4,5]. We clone a male determinant ZmGa1P at the Ga1 locus and reveal that expression of this pollen-specific PME can overcome the barrier in the Ga1-S silks. The interaction of ZmGa1P and another pollen-specific PME, ZmPME10-1, may form a protein complex to maintain the equilibrium of the apical cell wall dynamics during pollen tube growth, offering a mechanistic view for maize UCI

Methods

Results

Conclusion