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

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

Poster Abstract - 4.10

AN INTEGRATED APPROACH FOR ADDRESSING HETEROSIS IN MAIZE

PÈ M.E.*, PEA G.*, VILLA M.*, LANDI P.**, FRASCAROLI E.**, MORGANTE M.***, CATTONARO F.***

*) Dip. di Genetica e di Biologia dei Microrganismi, Milano

**) Dip. Scienze e Tecnologia Agroambientali

***) Dip. Produzione Vegetale e Tecnologia Agraria, Udine

heterosis, maize, QTLs, gene expression

Introduction

An integrated approach, in which extensive transcriptional characterization is combined to modern quantitative genetics is being applied to gain some understading of the molecular bases of heterosis. The exploitation of heterosis in plant breeding is considered one of the most revolutionary advancement in plant improvement. However, despite a long story of successes, there is still a striking gap between the extensive agricultural practice of hybrid vigor utilization and our understanding of the cause of such phenomenon. Both biometrical and molecular marker approaches are producing a huge amount of useful information concerning the genetic basis of complex traits, but, due to the fact that the structural and functional characteristics of the loci controlling the variability of the traits are for the most cases unknown, the complete exploitation of the information produced is somehow impaired. The application of genomics is likely to provide the necessary tools for analyzing transcriptional levels of a large number of genes and their regulation. This should allow to assess the importance of gene expression in determining heterosis.

Genetic design

Appropriate plant material was produced, to provide a common set of genotypes for each experimental approach and to allow data integration. The material meets two contrasting needs: sufficient complexity in order to allow an accurate genetic interpretation of the phenotypic values, and simple genetic design to ease molecular biology analysis. In particular a population of 142 recombinant inbred lines (RILs), obtained from the original cross B73 x H99 was used for the production of three pseudo-back cross (PBC) populations by crossing each of the 142 RIL with both the original parental lines (PBC-P1 and -P2) and their F1 hybrid (PBC-F1). In addition, a tester population (TC) was also produced, by crossing each of the 142 RIL with tester line Mo17. Owing to the mating design adopted, the mapping population of reference is the B73 x H99 RILs. This population has been already characterized for more than 200 molecular markers, mainly Simple Sequence Repeats and AFLPs.

Phenotypic evaluation and QTL mapping

All the populations described (i.e. RILs per se, PBC-P1, PBC-2, PBC-F1 and TC, for a total of 716 genotypes, were grown in three locations (2 reps per location). Data for components of vegetative growth, plant cycle and yield were collected and analyzed, to identify the underlying QTLs. Emphasis is placed on heterotic effect evaluation. Preliminary results concerning plant vigor are discussed.

Transcription profiling

A comparison of the expression profiles of sets of genes in the hybrid and in the corresponding inbred parents is being used to identify the components of the genetic circuits that control heterosis. A set of DNA microarrays on glass slides containing about 5000 non redundant maize ESTs (Unigene1) produced at the University of Arizona were hybridized with fluorescently labelled mRNAs extracted from young seedlings. Preliminary results are presented. Furthermore, to analyze the existence of a preferential expression for one of the two parental alleles (imprinting) in the F1 hybrid, allele-specific oligonucleotides were designed for several genes and are currently being used in RT-PCR experiments. We will discuss other approaches such as the analysis of the role of miRNAs and antisense RNAs.