Plant Organ Primordia

Abstract

The shoot apical meristem (SAM) in plants is composed of totipotent cells that generate the major plant organs including leaves and flowers. Within the SAM synthesis and movement of auxin creates a hormonal flux. In production of leaf primordia, the hormonal flux alters a series small ribonucleic acids (RNAs) that impact the expression of homeotic genes. This results in the generation of a WUSCHEL/CLAVATA feedback loop that generate niches that result in the placement of leaf primordia. This placement of leaf primordia generates the overall phyllotaxis and nodal architecture that defines the major plant body. In perennial plants, seasonal cues alter primordia development resulting in shifts between true leaves and bud scales creating the overwintering meristem. How the transition between bud scales and leaf primordia occurs in unclear. Key Concepts The initiation of leaf primordia at nodes is regulated by an auxin gradient within the SAM. A series of homeotic genes are associated with both SAM formation and establishment of leaf primordia and leaf organ symmetry including Knotted1, WUSCHEL‐RELATED Homeobox 1 and CLAVAT‐type (CLV) homoeotic genes. Small RNAs play a critical role in the developmental processes associated with the SAM development. Auxin flux is directed by PIN1 transporter polarity controlled by MONOPTEROS . Responses to seasonal variation alter leaf primordia development.