Barren Mutants in Maize-A Case Study in Plant Signaling

Abstract

Barren in this context indicates the complete lack of female organs, not just flowers, but the absolute lack of even female (ear) initials in the maize plant. There are at least 5 non-allelic genes in maize that when mutated cause barrenness. This has been verified by extensive allelic tests. The phenotype of each of these genes is generally similar in the female part of the plant. There is a phenotypic change in the tassel, that is quite obvious in the plants in the field, though admittedly, this has not been exhaustively verified by sufficient out crossing. Most any maize geneticist or breeder that is familiar with plants in the maize genetic or breeding nursery has observed the relationship of the maturing male and female components in the plants. In almost every case (there are occasional exceptions) the male flowering and pollen-shed occurs before the female begins silking. The gap between the two events varies, from 1 day to almost the end of the pollen-shedding period. It has been anecdotally assumed that hormones in the tassel control the initiation of female activity. The tassel appears to repress the female receptivity (silking) until the pollen shedding begins. This is only anecdotal and the necessary experiments have not been made to clearly show this relationship. There are mutants that vary this process but these have not been coupled with physiological investigations. Though the ba4 mutant arose in a transposon plot, the necessary molecular confirmation of this mutant has not confirmed a transposon insert. The behavior of this mutant illustrates some interesting features. The mutant expression is characterized by plants that are typically barren. The barren plants are unilaterally susceptible to anthracnose. In a segregating row, only the barren plants show anthracnose disease symptoms. The factor that is deficient and causes barrenness is suggestive that the mutant effect makes the plant susceptible to anthracnose infection. This mutant is predominantly recessive but not entirely. In crosses of these barren (obviously, as male) on to assorted wild type plants (+/+ x ba4/ba4), there is a low frequency of “escapes”, that is, plants are ba4 and barren. But not entirely, because late, after the tassel has been fully spent, even dried, and probably 30 days, a small deformed ear appears on the very last leaf, very low in the plant. Hypothesis on ba4: That a hormone is suppressing ear formation and thus barrenness. When the plant is nearing senescence, the hormone is depleted and the ear initial finally becomes evident.