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

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.

The ASYMMETRIC LEAVES Complex Employs Multiple Modes of Regulation to Affect Adaxial-Abaxial Patterning and Leaf Complexity

“…Likewise, adaxial-abaxial leaf polarity, which directs the acquisition of distinct cell fates within the leaf's adaxial/ top and abaxial/bottom domains, must be carefully controlled. The boundary between these domains drives the flattened outgrowth of the leaf (Waites and Hudson, 1995), and slight perturbations in either adaxial or abaxial identity cause progressive leaf curling with severe consequences for physiological function (Lang et al, 2004;Zhang et al, 2009;Nakata et al, 2012). Adaxial-abaxial leaf polarity in particular poses an unusual and mechanistically challenging problem, namely, how to create a stable boundary within the plane of a long and wide, but shallow, structure.…”

Genetic Framework for Flattened Leaf Blade Formation in Unifacial Leaves ofJuncus prismatocarpus

“…The establishment of adaxial-abaxial polarity in bifacial leaves is regulated by overlapping and antagonistic genetic interactions involving several distinct transcription factors and small regulatory RNAs (Husbands et al, 2009). In both eudicots and monocots, these include members of the Class III Homeodomain Leucine Zipper (HD-ZIPIII) gene family (McConnell et al, 2001;Juarez et al, 2004;Itoh et al, 2008b), which specify adaxial identity and are expressed in the adaxial domain of leaves, and KANADI Kerstetter et al, 2001;Candela et al, 2008;Zhang et al, 2009) and AUXIN RESPONSE FACTOR3 (ARF3)/ETTIN (ETT) genes (Pekker et al, 2005;Itoh et al, 2008a), which are expressed abaxially, where they specify abaxial identity.…”

SEMI-ROLLED LEAF1 Encodes a Putative Glycosylphosphatidylinositol-Anchored Protein and Modulates Rice Leaf Rolling by Regulating the Formation of Bulliform Cells

“…sll1 mutant exhibits extremely incurved leaves with ectopic formation of bulliform cells in abaxial surfaces due to the defective development of sclerenchymatous cells at the abaxial side of leaf blades. Enhanced expression of SLL1 also leads to rolled leaves due to the stimulated phloem development at the abaxial side and suppressed development of bulliform cells and sclerenchyma at the adaxial side (Zhang et al, 2009). Ectopic expression of micro-RNA166-resistant version of the OsHB1 gene, a member of class III homeodomain Leu zipper family, results in adaxially rolled leaves with reduced sclerenchyma and formation of bulliform cells at the abaxial side (Itoh et al, 2008).…”

“…The SHALLOT-LIKE1 (SLL1)/RL9 gene encodes a transcription factor of KANADI family and regulates leaf abaxial cell development (Yan et al, 2008;Zhang et al, 2009). sll1 mutant exhibits extremely incurved leaves with ectopic formation of bulliform cells in abaxial surfaces due to the defective development of sclerenchymatous cells at the abaxial side of leaf blades.…”