GENETIC STUDY AND AGRONOMIC EVALUATION OF BRACHYTIC 2 MUTANT IN MAIZE

In maize there are three types of brachytic mutants (br1, br2 and br3) showing short stature and a gibberellins-insensitive phenotype. So far only the brachytic 2 gene has been cloned and it encodes for a putative protein of the Multidrug Resistant (MDR) class of P-glycoproteins (PGPs) that could be involved in polar movement of auxins. We isolated a new recessive mutation of br2 gene (named br2-23) and with the aim of study its interactions with the other brachytic mutations we produced double mutants that showed an additive effect on the stature with respect to the single mutants br1, br2 and br3 and abnormal growth. In the progeny of the selfed br2 br3 double mutant we observed various defective seedlings, mirroring an altered embryo development and growth, which also suggested a role for the br3 gene in auxin transport. Expression analysis of the auxin efflux transporters codified by ZmPIN1 genes supports this finding, showing the up-regulation of the ZmPIN1a gene in the br3 mutant. These single and double mutants appear to be useful tools to study the genetics of plant height and to investigate auxin transport in plants. In addition agronomic trials were set to evaluate the performances of br2 mutation in different hybrid combinations.