Proceedings of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress

Salsomaggiore Terme, Italy - 26/29 September, 2001

ISBN 88-900622-1-5

Poster Abstract

NEW MALE STERILE MUTANTS OF MAIZE

GATTI E., GALLAVOTTI A., PERINI D., PÈ M.E.

Dipartimento di Genetica e di Biologia dei Microrganismi, Università di Milano

Although the pollen grain is a rather simple two- or three-celled organism, the construction of a functional male gametophyte involves a complex system of developmental processes, which requires the activity of a large set of genes. A direct approach to detect genes controlling pollen development is based on the study of single gene mutants affecting pollen characteristics and gametophytically expressed. A large number of nuclear male sterile mutants has been already described in many species, however very few are post-meiotic male sterile mutations. Here we present our results concerning the identification of gametophytic male sterile mutants (gaMS) in maize, by screening two tagging populations. The interest in gametophytically expressed genes is emphasized by the fact that, since the male gametophyte genome is haploid, pollen cytological analysis enables to uncover recessive mutations related to basal metabolism, which could be lethal for the sporophyte. In order to identify pollen grain abnormalities, anthers were collected prior to anthesis and pollen was analysed by means of optical microscope.

Ac-Ds tagging population. Selfing plants of a line containing the purple pericarp mutable allele (P-ww), due to an Ac transposable element insertion, we obtained several ears showing twin-sectors, indicating Ac early (and possible germinal) excision. Families were derived from each twin sector and analysed for the presence of male sterile mutations. A total of 5 independent gaMS mutants were identified.

RescueMu tagging population. A large tagging population has been produced within the frame of the Maize Gene Discovery Project (www.zmdb.iastate.edu), which is characterized by the presence of engineered Mutator-1 elements. RescueMu tagging population has been designed to ease the recovery of genomic regions flanking the inserted transposable element. During a three-year field trial more than 1000 families were screened, analysing a minimum of 8 plants per family, for the presence of mutations affecting male fertility.

Classes of mutants. Pre-meiotic and post-meiotic mutants were both identified. Pre-meiotic mutants could be classified in three classes: a) mutants in which no anthers were produced; b) mutants with small, but empty anthers; c) mutants with fully developed anthers, containing fully sterile pollen grains. Post-meiotic mutants were characterized by a 1:1 ratio of fertile and sterile pollen grains within a single anther. Three different types of gaMS mutants were classified. Type I: 50% sterility, due to completely collapsed pollen grains. Type II: 50% sterility, in which mutated pollen grains are smaller in size, but show the presence of starch. Type III: 50% sterility, in which abnormal pollen grains are smaller in size and do not have any starch. In addition, several families were characterized by different level of male sterility, ranging from 50% to up to 99%.