The classical maize mutant ramosa3 (ra3) has branched ears and more highly branched tassels due to a reduction in meristem determinacy, and encodes a trehalose-6-phosphate phosphatase (TPP) that degrades trehalose-6-phosphate (T6P) to trehalose. T6P has emerged as an important regulator, however, how RA3 controls meristem function remains enigmatic.
In order to find additional factors involved in RA3 function, ra3 was mutagenized to identify enhancers. We found four alleles of tpp4, a paralog of RA3. TPP4 is expressed in the same domain as RA3, and its expression is upregulated in ra3 mutants, indicating functional redundancy. All tpp4 alleles have amino acid substitutions in conserved residues, and some retain significant enzymatic activity. Nonetheless, all alleles have similar phenotypic strength, suggesting that there is no straightforward relation between TPP activity and phenotype. In agreement with this, no change in T6P levels could be detected in these mutants. tpp4 mutants also affect the floral transition, suggesting that the function of T6P in flowering time regulation, first reported in Arabidopsis, is conserved in maize. Preliminary interaction data suggests that RA3 interacts with nuclear proteins and may play a moonlighting function in gene regulation.