Comparative Transcriptional Profiling Established the Awn as the Major Photosynthetic Organ of the Barley Spike While the Lemma and the Palea Primarily Protect the Seed

The lemma, palea, and awn of a barley ( Hordeum vulgare L.) spike are photosynthetic organs that supply the developing seed with carbohydrates. The lemma and palea also enclose the seed and protect it from pathogens and insects. Despite the important roles they play, little information exists on gene expression in these organs that identifies their function. In this study, we compared gene expression among the lemma, palea, awn, and developing seed of barley during grain filling using the Barley1 Genome Array to identify highly expressed genes involved in the primary function of these organs. Hierarchical clustering and mixed model analysis revealed that the lemma and palea have closely related gene expression patterns. In addition, the lemma and palea overexpressed defense‐related genes compared with the awn. The awn preferentially expressed genes for photosynthesis, the biosynthesis of chlorophyll and carotenoids, and reactive oxygen species scavenging. This suggests the lemma and palea are mainly protective organs whereas the awn is primarily a photosynthetic structure. The seed was enriched with genes for the biosynthesis of starch, storage proteins, enzyme inhibitors, and cell proliferation.