A Pectin Methylesterase ZmPme3 Is Expressed in Gametophyte factor1-s (Ga1-s) Silks and Maps to that Locus in Maize (Zea mays L.)

Abstract

The ga1 locus of maize confers unilateral cross incompatibility, preventing cross pollination between females carrying the incompatible Ga1-s allele and males not carrying a corresponding compatible allele. To characterize this system at the molecular level, we carried out a transcript profiling experiment in which silks from near isogenic lines carrying the Ga1-s and ga1 alleles were compared. While several differentially expressed genes were identified, only one mapped to the known location of ga1. This gene is a pectin methylesterase (PME), which we designated as ZmPme3, and is present and expressed only in Ga1-s genotypes. While a functional ZmPME3 is not present in the ga1 genotypes examined, a pectin methylesterase gene cluster is found in ga1 genotypes. The gene cluster in W22 contains 58 tandem full-length or partial PME pseudo genes. These data combined with a wealth of previously published data on the involvement of PMEs in pollen tube growth suggest a role for cell wall modification enzymes in the pollen exclusion component of Ga1-s gametophytic incompatibility. Consistent with this role, a third allele which lacks the female function of Ga1-s, Ga1-m, has a mutationally inactivated version of ZmPme3.

A Silk-Expressed Pectin Methylesterase Confers Cross-Incompatibility Between Wild and Domesticated Strains of Zea mays

“…qRT-PCR confirmed this expression difference (Fig.2b). Pertunda is not present in the maize B73 reference genome, which is consistent with the mapping data, and the closest homologs of Pertunda are located at the ga1 locus ( 10 ).…”

“…The most similar gene to Pertunda is a candidate PME gene for Ga1-female function. This gene, termed ZmPME3 , was found to be expressed in the silks of Ga1-s , but not in ga1 silks, and ZmPME3 was located to the Ga1 mapping region( 10 ). Alignment of the ZmPME3 and Pertunda show that the two PMEs differ in nine amino acids (Fig.…”

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

“…This study identified a pollen tube-specific PME, a type-II/group 1 PME (lacking a pro-region) 25 , 26 , as a pollen determinant of the Ga1 locus in maize UCI. Another type-II PME, ZmPME3, has been reported to function as a female determinant candidate 15 . Maize potentially evolved a previously undescribed PME-mediated mechanism to control UCI, which is distinct from the known mechanisms that govern SI and CI in higher plants, such as the RNase-mediated system in Solanaceae, Rosaceae, and Plantaginaceae 12 , 13 , 27 and the peptide ligand-kinase system in Brassicaceae and Papaveraceae 28 – 30 .…”

“…During fertilization, Ga1-S plants completely reject the pollen of ga1 due to the female barrier but accept pollen of Ga1-S and Ga1-M haplotypes, though the selfing and reciprocal crosses are compatible 2 , 3 . Many efforts have been made to identify the male and female determinants 3 , 11 , 15 . Recently, ZmPME3 in the Ga1 region was found to be specifically expressed in the silks of Ga1-S plants, serving as a likely candidate for the female function 15 .…”

“…Many efforts have been made to identify the male and female determinants 3 , 11 , 15 . Recently, ZmPME3 in the Ga1 region was found to be specifically expressed in the silks of Ga1-S plants, serving as a likely candidate for the female function 15 . However, the mechanism underlying the male function in maize UCI remains elusive.…”