Patterning a Leaf by Establishing Polarities.

Darren Manuela,Mingli Xu

doi:10.3389/fpls.2020.568730

Abstract

Leaves are the major organ for photosynthesis in most land plants, and leaf structure is optimized for the maximum capture of sunlight and gas exchange. Three polarity axes, the adaxial–abaxial axis, the proximal-distal axis, and the medial-lateral axis are established during leaf development to give rise to a flattened lamina with a large area for photosynthesis and blades that are extended on petioles for maximum sunlight. Adaxial cells are elongated, tightly packed cells with many chloroplasts, and their fate is specified by HD-ZIP III and related factors. Abaxial cells are rounder and loosely packed cells and their fate is established and maintained by YABBY family and KANADI family proteins. The activities of adaxial and abaxial regulators are coordinated by ASYMMETRIC LEAVES2 and auxin. Establishment of the proximodistal axis involves the BTB/POZ domain proteins BLADE-ON-PETIOLE1 and 2, whereas homeobox genes PRESSED FLOWER and WUSCHEL-RELATED HOMEOBOX1 mediate leaf development along the mediolateral axis. This review summarizes recent advances in leaf polarity establishment with a focus on the regulatory networks involved.

Highlights

Leaves are the major organ for photosynthesis and are specified for maximum capture of sunlight and minimum loss of water
The morphological difference between adaxial and abaxial cells becomes apparent at later stages of leaf development, the expression of adaxial–abaxial identity genes is observed in globular-stage cotyledons and leaf primordia, suggesting that the establishment of adaxial–abaxial polarity occurs very early in leaf development (Eshed et al, 2001; Kerstetter et al, 2001; Emery et al, 2003)
REV directly activates SHOOT MERISTEMLESS (STM) in leaf axils to promote axillary meristem formation (Shi et al, 2016). This regulation appears to be promoted by DORNROSCHEN (DRN) and DORNROSCHEN-LIKE (DRNL), two AP2/ERF transcription factors that physically interact with REV and bind to a region near the transcriptional start site of STM (Zhang et al, 2018)

Summary

Darren Manuela and Mingli Xu*

Leaves are the major organ for photosynthesis in most land plants, and leaf structure is optimized for the maximum capture of sunlight and gas exchange. The adaxial–abaxial axis, the proximal-distal axis, and the medial-lateral axis are established during leaf development to give rise to a flattened lamina with a large area for photosynthesis and blades that are extended on petioles for maximum sunlight. Tightly packed cells with many chloroplasts, and their fate is specified by HD-ZIP III and related factors. Abaxial cells are rounder and loosely packed cells and their fate is established and maintained by YABBY family and KANADI family proteins. Establishment of the proximodistal axis involves the BTB/POZ domain proteins BLADE-ON-PETIOLE1 and 2, whereas homeobox genes PRESSED FLOWER and WUSCHEL-RELATED HOMEOBOX1 mediate leaf development along the mediolateral axis.

INTRODUCTION

YAB LUG

Establishment of Abaxial Identity by KANADI and YABBY Proteins

FUTURE PERSPECTIVES