Maize Genetics
Cooperation Newsletter vol 84 2010
Please Note: Notes
submitted to the Maize Genetics Cooperation Newsletter may be cited only with
consent of authors.
MILANO, ITALY
University of Milano
The brachytic 2 and 3 maize
double mutant shows alterations in plant growth and embryo development
--Pilu,
R; Villa, D; Cassani, E; Durante, M; Cerino Badone, F; Sirizzotti, A; Bucci A
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.
With the aim of elucidating the relationship between brachytic 2 and 3 mutations we produced by crossing the br2 br3 double mutant and we
observed for the first time a strong additive effect regarding plant stature
and architecture and also an involvement of these two genes in embryo development.
In fact br2 br3 plants, named �gnome�, showed shorter internodes with curled and wrinkled leaves compared
to the monogenic brachytic
mutation (Fig. 1). The measurement of these plants showed that gnomes are shorter by about 85% compared with the
wild type plant. Starting from these gnome plants we performed four cycles of
selfing to produce near-isogenic lines to use for the following studies. We
noticed high sterility of these plants with the presence of a few seeds in the ears harvested. With
the aim of understanding whether the br2/br2 br3/br3 seedlings were, in some way,
affected by interaction between these two brachytic mutations we germinated on
paper the offspring of selfed gnome (br2 and br3 seedlings do not show any obvious difference vs wt seedlings,
data not shown). We observed a strong effect regarding seedling morphology, in
fact as shown in Figure 2 we identified defective seedlings roughly classified
in four phenotypic classes: stunted plants like a dwarf mutant (Fig. 2B), seedlings
with the first leaf that remains closed, named tube (Fig. 2C), seedlings with
distorted growth (Fig. 4D) and
seedlings without a shoot, named shootless (Fig. 2E). We also noticed an
high level of non-germinated seeds, as reported in Table 1 where we summarize
the quantitative data regarding this phenotypic distribution (taking together
all the segregation data obtained from the progeny of gnome plants). We also
observed a different percentage of
distribution of seedling abnormalities among the different selfed br2/br2
br3/br3 near
isogenic lines developed, ranging
from only non-germinated
seeds to almost only stunted seedlings (data not shown). Of course the only br2/br2
br3/br3
phenotypic class able to grow was the stunted seedlings that at maturity became gnome plants.
In conclusion, the results here
reported suggest for the first
time, an important new role of br2 and br3 genes in maize embryogenesis which could contribute to
answering several open questions regarding PAT and embryo development in maize and other cereals.
Table 1. Segregation of mutant seedling phenotypes
obtained by selfing the br2/br2
br3/br3 gnome
plants. The seeds were
germinated on imbibed paper. |
|||
cross |
|
segregation |
|
br2/br2 br3/br3 selfed |
gnome |
abnormal seedlings |
not germinated |
|
116 (38.66%) |
49 (16.33%) |
135 (45%) |
Figure 1. From left to right are shown wild type, br2, br3
and gnome plants at maturity (A). (B) gnome phenotype in
detail.
Figure 2. Range of
abnormalities showed by br2br2 br3br3 seedlings. (A) wt seedling, (B) dwarfing-like
seedling that will became gnome at maturity, (C) �tube� seedling: the first leaf that remains closed, (D)
seedling with distorted growth, (E) shootless seedling.