Molecular and Hormonal Regulation of Leaf Morphogenesis in Arabidopsis.

Shahid Ali,Linan Xie,Naeem Khan

doi:10.3390/ijms21145132

Abstract

Shoot apical meristems (SAM) are tissues that function as a site of continuous organogenesis, which indicates that a small pool of pluripotent stem cells replenishes into lateral organs. The coordination of intercellular and intracellular networks is essential for maintaining SAM structure and size and also leads to patterning and formation of lateral organs. Leaves initiate from the flanks of SAM and then develop into a flattened structure with variable sizes and forms. This process is mainly regulated by the transcriptional regulators and mechanical properties that modulate leaf development. Leaf initiation along with proper orientation is necessary for photosynthesis and thus vital for plant survival. Leaf development is controlled by different components such as hormones, transcription factors, miRNAs, small peptides, and epigenetic marks. Moreover, the adaxial/abaxial cell fate, lamina growth, and shape of margins are determined by certain regulatory mechanisms. The over-expression and repression of various factors responsible for leaf initiation, development, and shape have been previously studied in several mutants. However, in this review, we collectively discuss how these factors modulate leaf development in the context of leaf initiation, polarity establishment, leaf flattening and shape.

Highlights

Leaves are the primary organs responsible for photosynthesis and photoperception, and play a key role in plant growth
The main focus of this review is to summarize the current knowledge and discuss the several fundamental aspects of leaf development, including a genetic regulatory framework that contributes to leaf initiation, leaf polarity determination, and leaf outgrowth and flattening
We focused on the size and growth of the Arabidopsis thaliana model plant in which the determined organ is regulated by several genetic and environmental factors

Summary

Introduction

Leaves are the primary organs responsible for photosynthesis and photoperception, and play a key role in plant growth. The CLV3-related signaling pathway in the stem cell domain is demonstrated by the diffusion of CLV3 peptide towards the inner layer of the meristem, where at least three receptor complexes recognize it These receptor complexes include CLV1, CLV2, CORYNE (CRN), RECEPTOR-LIKE PROTEIN KINASE2 (RPK2), and BARELY ANY MERISTEM1 (BAM1/2) and represses the expression of WUS [42,43], which is crucial for the stem cell population [79]. In Arabidopsis, WUS represses those TFs-coding genes that are involved in differentiation, for example, KANADI (KAN1), (KAN2), AS2, YABBY3 (YAB3), KNAT1/BREVIPEDICELLUS (BP), and BELL1-LIKE HOMEODOMAIN5 (BLH5) [80,81] The identification of these direct interactions can contribute to the understanding of the molecular network but with limitations to explain the mechanisms by which WUS controls stem cell homeostasis. PIN1 drains auxin toward the base of the leaf primordium by inducing vascular tissue differentiation in the L2 and L3 layers [83,87]

Gene Functioning in Leaf Initiation

Leaf Outgrowth and Expansion

Leaf Margins Serrations

Developmental Functions of Micrornas

Conclusions and Future Perspectives