Pre-anthesis light signaling of sheathed developing barley inflorescences defines floral fate

The pre-anthesis inflorescence greening (PAIG) is a distinctive developmental feature in the members of the Triticeae such as barley, wheat and rye. In barley (Hordeum vulgare L.), floral survival and fertility are major determinants of grain yield, yet the physiological processes supporting early inflorescence development remain poorly understood. Here, we investigated PAIG, a light-dependent chlorophyll accumulation occurring while immature inflorescences are still enclosed by leaf sheaths, and its role in overall inflorescence development. Using chlorophyll autofluorescence imaging and chlorophyll quantification, we found that PAIG in barley initiates at a surprisingly early developmental stage, when developing spikes are still enclosed by leaf sheaths. PAIG first appears in the central rachis and then progressively spreads to the spikelet primordia and other floral organs. Using a non-destructive dark treatment that prevents light exposure to developing inflorescences, we showed that inhibiting PAIG does not impact floral initiation. Yet, the dark treatment significantly decreases floral survival and pollen viability, especially at the tip of the inflorescence. This highlights the essential role of light-mediated PAIG in determining floral fate. Finally, analysis of natural variation for PAIG revealed a strong positive correlation between the extent of PAIG and floral survival. Our findings establish PAIG as an underappreciated hidden trait that supports floral viability and reproductive success, with implications to enhance grain yield potential in cereals.