SHALLOT-LIKE1 Is a KANADI Transcription Factor That Modulates Rice Leaf Rolling by Regulating Leaf Abaxial Cell Development

Guang-Heng Zhang,Qian Xu,Xu-Dong Zhu,Hong-Wei Xue,Qian Qian

doi:10.1105/tpc.108.061457

Abstract

As an important agronomic trait, rice (Oryza sativa L.) leaf rolling has attracted much attention from plant biologists and breeders. Moderate leaf rolling increases the photosynthesis of cultivars and hence raises grain yield. However, the relevant molecular mechanism remains unclear. Here, we show the isolation and functional characterization of SHALLOT-LIKE1 (SLL1), a key gene controlling rice leaf rolling. sll1 mutant plants have extremely incurved leaves due to the defective development of sclerenchymatous cells on the abaxial side. Defective development can be functionally rescued by expression of SLL1. SLL1 is transcribed in various tissues and accumulates in the abaxial epidermis throughout leaf development. SLL1 encodes a SHAQKYF class MYB family transcription factor belonging to the KANADI family. SLL1 deficiency leads to defective programmed cell death of abaxial mesophyll cells and suppresses the development of abaxial features. By contrast, enhanced SLL1 expression stimulates phloem development on the abaxial side and suppresses bulliform cell and sclerenchyma development on the adaxial side. Additionally, SLL1 deficiency results in increased chlorophyll and photosynthesis. Our findings identify the role of SLL1 in the modulation of leaf abaxial cell development and in sustaining abaxial characteristics during leaf development. These results should facilitate attempts to use molecular breeding to increase the photosynthetic capacity of rice, as well as other crops, by modulating leaf development and rolling.

Highlights

The three-dimensional structure of the plant leaf is crucial for its functions, including light capture, carbon fixation, and gas exchange for photosynthesis (Govaerts et al, 1996)
This study expands our knowledge of rice leaf development, especially the roles of leaf sclerenchymatous cells
The form of the dicot leaf is determined strongly by the mesophyll cell type; altered polarity in spongy tissue or palisade tissues will result in leaf rolling

Summary

INTRODUCTION

The three-dimensional structure of the plant leaf is crucial for its functions, including light capture, carbon fixation, and gas exchange for photosynthesis (Govaerts et al, 1996). The maize gene ROLLED LEAF1 (RLD1) encodes a HDZIP III family transcription factor and is involved in adaxial specification (Juarez et al, 2004b). The middle vein on the maize leaf contains polarized xylem and phloem In contrast with those of dicots, the mesophyll cells of some grasses, including maize and rice, have a uniform configuration without polarization (there is only spongy parenchyma in leaf), termed isobilateral mesophyll (Fahn, 1990); the development and regulation of polarity in isobilateral leaves remain to be elucidated. SLL1 is crucial in polarity formation and helps to direct the development of the leaf abaxial cell layer It is involved in the transdifferentiation of mesophyll cells to sclerenchymatous cells through the modulation of PCD, highlighting a possible mechanism underlying leaf rolling in monocot plants

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