Natural Variation in the Flag Leaf Morphology of Rice Due to a Mutation of the NARROW LEAF 1 Gene in Oryza Sativa L

By Taguchi-Shiobara, Fumio; Ota, Tatsuya et al. | Genetics, October 2015 | Go to article overview

Natural Variation in the Flag Leaf Morphology of Rice Due to a Mutation of the NARROW LEAF 1 Gene in Oryza Sativa L


Taguchi-Shiobara, Fumio, Ota, Tatsuya, Ebana, Kaworu, Ookawa, Taiichiro, Yamasaki, Masanori, Tanabata, Takanari, Yamanouchi, Utako, Wu, Jianzhong, Ono, Nozomi, Nonoue, Yasunori, Nagata, Kazufumi, Fukuoka, Shuichi, Hirabayashi, Hideyuki, Yamamoto, Toshio, Yano, Masahiro, Genetics


THE leaf of grasses typically consists of a relatively narrow blade and sheath enclosing the stem, and venation is parallel in the blade and the sheath (Esau 1977). Because large leaves intercept more light, the leaf area of the blade strongly affects final yield in cereal crops (Watson 1952). To produce plants that intercept light efficiently, leaf angle has been a target in breeding programs because erect leaves can capture more sunlight (Sinclair and Sheehy 1999). It was demonstrated that a brassinosteroid-deficient mutant with erect leaves showed increased grain yield under dense planting conditions (Sakamoto et al. 2005). It is also essential to understand the mechanism of development and the natural variations in morphology of the flag leaf since photosynthesis in the top three leaf blades of the plant, especially flag leaf, makes the largest contribution to the grain yield of rice (Tanaka 1958; Yoshida 1972).

The developmental processes of the flag leaf are the same as those of other leaves. In rice, the longitudinal strands in the leaf comprise the midrib, large vascular bundles, and small vascular bundles (Hoshikawa 1989). According to Inosaka (1962) and Itoh et al. (2005), the midrib and large vascular bundles initiate at the base of the leaf primordium and develop acropetally in the leaf and basipetally in the culm (stage P2 in leaf development). It takes about one plastochron to initiate a small vascular bundle after the initiation of the midrib. When the leaf sheath and blade start to differentiate(thebeginningofstageP3), small vascular bundles become visible between the large vascular bundles at the base of leaf primordia. Small vascular bundles form acropetally in the leaf blade and basipetally in the stem. Later (stage P3), a small vascular bundle develops between the midrib and a large vascular bundle near the leaf tip and extends basipetally through the leaf blade. Then, more small vascular bundles form between large vascular bundles sequentially from the midrib toward the leaf margin. After the rapid elongation of the leaf blade (stage P4) and the leaf sheath (stage P5), the leaf becomes mature and growth is complete (stage P6).

Natural variations in flag leaf size have been reported for 491 rice accessions from Japan and 666 accessions from other countries (Matsuo 1952). Flag leaves were wider in accessions from Java, western China, and Latin America and narrower in those from north China, central China, and Russia. Flag leaves were longer in accessions from Java and India, but shorter in those from Taiwan, central China, and south China. In genome-wide association studies (GWAS) of 413 diverse accessions, significant loci accounted for 24% of variance in the width of the flag leaf (WFL), and three loci on chromosomes 1, 4, and 7 contributed 5.7, 5.0, and 6.1% of phenotypic variance, respectively (Zhao et al. 2011).

The NARROW LEAF 1 (NAL1) gene was located at 31.2 Mb on chromosome 4 (hereafter, all genomic positions are based on Os-Nipponbare-Reference-IRGSP-1.0), close to one of the single-nucleotide polymorphisms contributing to the variation in WFL reported by Zhao et al. (2011). NAL1 was originally isolated as a gene affecting vascular patterns in a study on a classic dwarf mutant with a narrow leaf (Qi et al. 2008) and was later shown to affect WFL, total spikelet number per panicle, photosynthetic rate, and chlorophyll content (Chen et al. 2012; Fujita et al. 2013; Takai et al. 2013; Zhang et al. 2014). NAL1 encodes a plant-specific protein, and the nal1 mutant with an in-frame deletion of 10 amino acids in exon 4 showed reduced basipetal polar auxin transport and fewer longitudinal veins, compared with wild type (Qi et al. 2008). A recent analysis of mutant rice with a NAL1 null allele implied that NAL1 is also involved in control of the cell cycle and cell division from the initial stage of leaf development onward (Jiang et al. 2015).

The NAL1 gene exhibits natural variations that are associated with plant morphology in rice. …

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Natural Variation in the Flag Leaf Morphology of Rice Due to a Mutation of the NARROW LEAF 1 Gene in Oryza Sativa L
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