Wheat <i>VRN1</i> , <i>FUL2</i> and <i>FUL3</i> play critical and redundant roles in spikelet development and spike determinacy

Abstract

The spikelet is the basic unit of the grass inflorescence. In this study, we show that wheat MADS-box genes <i>VRN1</i>, <i>FUL2</i> and <i>FUL3</i> play critical and redundant roles in spikelet and spike development, and also affect flowering time and plant height. In the <i>vrn1ful2ful3</i>-null triple mutant, the inflorescence meristem formed a normal double-ridge structure, but then the lateral meristems generated vegetative tillers subtended by leaves instead of spikelets. These results suggest an essential role of these three genes in the fate of the upper spikelet ridge and the suppression of the lower leaf ridge. Inflorescence meristems of <i>vrn1ful2ful3</i>-null and <i>vrn1ful2</i>-null remained indeterminate and single <i>vrn1</i>-null and <i>ful2-</i>null mutants showed delayed formation of the terminal spikelet and increased number of spikelets per spike. Moreover, the <i>ful2</i>-null mutant showed more 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 mechanisms underlying wheat spikelet and spike development can inform future strategies to improve grain yield in wheat.