The heterochronic maize mutant Corngrass1 results from overexpression of a tandem microRNA

Abstract

Retention of juvenile traits in the adult reproductive phase characterizes a process known as neoteny, and speculation exists over whether it has contributed to the evolution of new species. The dominant Corngrass1 (Cg1) mutant of maize is a neotenic mutation that results in phenotypes that may be present in the grass-like ancestors of maize. We cloned Cg1 and found that it encodes two tandem miR156 genes that are overexpressed in the meristem and lateral organs. Furthermore, a target of Cg1 is teosinte glume architecture1 (tga1), a gene known to have had a role in the domestication of maize from teosinte. Cg1 mutant plants overexpressing miR156 have lower levels of mir172, a microRNA that targets genes controlling juvenile development. By altering the relative levels of both microRNAs, it is possible to either prolong or shorten juvenile development in maize, thus providing a mechanism for how species-level heterochronic changes can occur in nature.

Latent developmental and evolutionary shapes embedded within the grapevine leaf

“…Similarly, dramatic transitions to reproductive fates, reflecting the temporal development of meristems, have been described (Park et al ., 2012). An understanding of molecular clocks, regulating phase change through small RNAs (Chuck et al ., 2007; Wu et al ., 2009), and their signals, such as sugar (Yang et al ., 2013; Yu et al ., 2013), has come into focus. Vegetative, heteroblastic changes in leaf shape have an intimate relationship with reproductive transitions, as demonstrated by recent work linking natural variation in a floral repressor, FLOWERING LOCUS C (FLC), with changes in leaf morphology between species (Cartolano et al ., 2015).…”

Molecular evolution and selection of a gene encoding two tandem microRNAs in rice

“…These results indicate that the MIR156b/c locus is highly conserved at least in rice, maize and sorghum and perhaps in all cereals. The function of MIR156b/c also appears to be conserved in rice and maize as the phenotypic changes observed in transgenic plants overexpressing miR156b (rice; [13]) or miR156b/c (maize; [19]) are similar.…”

“…The conserved function of MIR156b/c in maize and rice led us to investigate whether selection forces have acted on it during the origin and domestication of rice [13,19]. To answer this question, genomic sequences of the MIR156b/c locus were amplified from 30 rice cultivars and 15 wild rice accessions.…”

“…In maize the Corngrass1 (Cg1) gene also encodes tandem MIR156 genes (MIR156b and MIR156c). The dominant Cg1 mutant shows dwarfing, multiple-tillers and a bushy phenotype due to overexpression of miR156b/c [19].…”

“…Transcription factors, in turn, are major targets of miRNAs. For example, tga1, a transcription factor of the SPL family known to have had a role in the domestication of maize from teosinte, is one of the targets of Cg1 [19].…”