Using maize as a model to study pollen tube growth and guidance, cross-incompatibility and sperm delivery in grasses

Abstract

We propose to develop maize (Zea mays) as a model to investigate the above-described processes to understand the associated intra- and interspecific crossing barriers in grasses. Many genetic, cellular and biotechnological tools including the completion of a reference genome (inbred line B73) have been established in the last decade and many more maize inbred genomes are expected to be available soon. Moreover, a cellular marker line database as well as large transposon insertion collections and improved Agrobacterium transformation protocols are now available. Additionally, the processes described above are well studied at the morphological level and a number of mutants have been described already, awaiting disclosure of the relevant genes. The identification of the first key players in pollen tube growth, guidance and burst show maize to be an excellent grass model to investigate these processes in more detail. Here we provide an overview of our current understanding of these processes in Poaceae with a focus on maize, and also include relevant discoveries in eudicot model species.

Massively Parallelized Pollen Tube Guidance and Mechanical Measurements on a Lab-on-a-Chip Platform

“…The maize pollen starts to germinate within 5 minutes after contact with the stigma [2] and can grow 300 mm long in the style to fertilize the ovary, amassing along its journey a record length-diameter ratio of around 12,000. This rapid tip-growth is driven by a dynamic and precisely regulated process involving ionic exchange, cell wall material metabolism, and cytoskeletal activity [3], necessitating high-throughput-assay platforms for phenotypic quantification.…”

Zygotic Genome Activation Occurs Shortly after Fertilization in Maize

“…The corresponding proteins play key roles in female gamete cell identity, as well as pollen tube guidance and burst in maize (reviewed in Dresselhaus et al, 2011Dresselhaus et al, , 2016. However, due to their polymorphic nature, no unambiguous homologs of the individual members were identified in the databases from Ensembl Compara or the Rice Genome Annotation Project.…”

Assessment of the potential for gene flow from transgenic maize (Zea mays L.) to eastern gamagrass (Tripsacum dactyloides L.)

“…However, the success of artificial hybridization was accomplished only with special techniques (Beadle 1980) such as removing husk leaves from maize ears, and cutting the maize silks to accommodate for shorter eastern gamagrass pollen tubes (Mangelsdorf and Reeves 1931; Bernard and Jewell 1985). The shorter maize silks eliminated one of the cross-incompatibility obstacles (lack of growth support for the eastern gamagrass pollen tube within the maize silk), however there are other late-acting barriers which prevent formation of hybrid zygote in most intergeneric crosses between grasses (Dresselhaus et al 2011). Utilization of embryo culture techniques (Randolph 1970; James 1979; Bernard and Jewell 1985) was also needed to generate these experimental hybrids between eastern gamagrass and maize.…”

“…Most experts agree that Tripsacum and maize do not naturally cross-pollinate in spite of growing in close proximity for centuries (Mangelsdorf and Reeves 1931; Randolph 1970; Beadle 1980; Dresselhaus et al 2011). No evidence was found for ongoing natural gene introgression between maize and Tripsacum although careful and extensive research was conducted across large number of populations from Mexico, Guatemala and South America (de Wet and Harlan 1978; de Wet et al 1981).…”