Rice transcription factors OsMADS2 and OsMADS4 regulate floret organ development: Deciphering their gene targets, traits and functions related to their unequal genetic redundancy

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PhD; 2023; Microbiology and cell biology

Organs in modern dicot flowers are positioned in concentric rings (whorls). The outermost whorl has green protective sepals, internal to which are showy petals, and the reproductive stamen and carpel whorls. Florets of rice, cereals and grasses evolved certain morphological and functionally distinct features in their non-reproductive organs. Striking among them are the highly modified petal analogs; called lodicules, and the large bract-like outermost organs named palea and lemma. The analogy of these modified rice floret organs to sepals and petals is debated. The two lodicules of rice florets are small (limited growth in Proximal-Distal axis), thick (extensive growth in Dorsal-Ventral axis) and are asymmetrically positioned to occupy only one half of the second whorl. They perform an important mechanical role in the partial opening of the flower for stamen emergence and subsequent closing. Their asymmetric position, small fleshy structure with many parenchymatous cell layers and their regulated physiology for swelling and collapse are critical for these functions.