Two WUSCHEL-related homeobox Genes, narrow leaf2 and narrow leaf3, Control Leaf Width in Rice

Abstract

Leaf shape is one of the key determinants of plant architecture. Leaf shape also affects the amount of sunlight captured and influences photosynthetic efficiency; thus, it is an important agronomic trait in crop plants. Understanding the molecular mechanisms governing leaf shape is a central issue of plant developmental biology and agrobiotechnology. Here, we characterized the narrow-leaf phenotype of FL90, a linkage tester line of rice (Oryza sativa). Light and scanning electron microscopic analyses of FL90 leaves revealed defects in the development of marginal regions and a reduction in the number of longitudinal veins. The narrow-leaf phenotype of FL90 shows a two-factor recessive inheritance and is caused by the loss of function of two WUSCHEL-related homeobox genes, NAL2 and NAL3 (NAL2/3), which are duplicate genes orthologous to maize NS1 and NS2 and to Arabidopsis PRS. The overexpression of NAL2/3 in transgenic rice plants results in wider leaves containing increased numbers of veins, suggesting that NAL2/3 expression regulates leaf width. Thus, NAL2/3 can be used to modulate leaf shape and improve agronomic yield in crop plants.

Genetic analysis of rice mutants responsible for narrow leaf phenotype and reduced vein number

“…Although each single mutant of narrow leaf2 (nal2) and nal3 shows no obvious phenotype, the nal2 nal3 double mutant produces very narrow leaves with a reduced number of veins (Cho et al, 2013;Ishiwata et al, 2013). These two genes belong to the WUSCHEL-RELATED HOMEOBOX (WOX) gene family and are orthologous to the PRESSED FLOWER (PRS)/WOX3 gene in Arabidopsis thaliana and the NARROW SHEATH genes in maize (Matsumoto and Okada, 2001;Nardmann et al, 2004).…”

“…These two genes belong to the WUSCHEL-RELATED HOMEOBOX (WOX) gene family and are orthologous to the PRESSED FLOWER (PRS)/WOX3 gene in Arabidopsis thaliana and the NARROW SHEATH genes in maize (Matsumoto and Okada, 2001;Nardmann et al, 2004). The NAL2 and NAL3 genes are extremely similar to each other, probably because of a recent segmental duplication of 2-3 Mb in chromosome 11 and 12 (Ishiwata et al, 2013). The nal1 mutant displays a reduction in the width of the leaf blade and the number of crown roots (Qi et al, 2008;Cho et al, 2014;Jiang et al, 2015).…”

“…The nal7 mutant and the nal2 nal3 double mutant were described previously (Fujino et al, 2008;Cho et al, 2013;Ishiwata et al, 2013). We focused on a new mutant line, CM1054, which also showed a narrow leaf phenotype.…”

“…To isolate triple mutants, we first chose plants homozygous for nal7 from the F2 plants by genotyping. It is very difficult to find the nal2 nal3 double mutation by genotyping, because NAL2 and NAL3 are highly similar to each other in nucleotide sequence, and the NAL3 gene is entirely deleted in the original nal2 nal3 mutant (Ishiwata et al, 2013). However, the nal2 nal3 double mutation can be identified by phenotypes such as narrow leaves and number of tillers, because neither of the single mutations show any phenotype (Cho et al, 2013;Ishiwata et al, 2013).…”

Repression ofAS2by WOX family transcription factors is required for leaf development in Medicago and Arabidopsis

“…[6][7][8][9][10][11] In monocots, this meristematic domain is maintained by the WOX3/PRS homologues, named NARROWSHEATH 1 and 2 (NS1 and NS2) in Zea Mays, 12 and NARROW LEAF2 and NAR-ROW LEAF3 in Oryza sativa. 13,14 In several other sequenced monocot-species, such as Musa acuminata, Sorghum bicolor, Brachypodium distachyon and Phyllostachys heterocycla, WOX3 homologues are all duplicated one or more times, suggesting their important roles in monocot plant development. In dicots, however, WOX3 usually exists as a single copy in the genome.…”