ABSTRACT
The spikelet is the basic unit of the grass inflorescence. In this study, we show that wheat MADS-box genes VRN1 and FUL2 play critical and redundant roles in the determination of spikelet meristem identity. Combined loss-of-function mutations of these two genes (vrn1ful2-null) were sufficient to revert lateral spikelet meristems into vegetative meristems in the spikes of tetraploid wheat. These plants were also unable to form a terminal spikelet and had an indeterminate inflorescence. The single vrn1-null and ful2-null mutants showed increased number of spikelets per spike, likely due to a delayed formation of the terminal spikelet. Mutations in these two genes and in the more distantly related paralog FUL3, also affected wheat heading time and stem elongation. The ful2-null mutant also showed a higher number of florets per spikelet, which together with a higher number of spikelets, resulted in a significant increase in the number of grains per spike in the field. Our results suggest that a better understanding of the basic mechanisms underlying wheat spike development can inform future strategies to improve grain yield in wheat.
SUMMARY STATEMENT The wheat MADS-box proteins VRN1 and FUL2 play critical and overlapping roles in the development of spikelets, which are the basic unit of all grass inflorescences.