Abstract
The leaf blade is the main photosynthetic organ and its morphology is related to light energy capture and conversion efficiency. We isolated a novel rice Dynamic Narrow-Rolled Leaf 1 (dnrl1) mutant showing reduced width of leaf blades, rolled leaves and lower chlorophyll content. The narrow-rolled leaf phenotype resulted from the reduced number of small longitudinal veins per leaf, smaller size and irregular arrangement of bulliform cells compared with the wild-type. DNRL1 was mapped to chromosome 7 and encoded a putative 3-deoxy-7-phosphoheptulonate synthase (DAHPS) which catalyzes the conversion of phosphoenolpyruvate and D-erythrose 4-phosphate to DAHP and phosphate. Sequence analysis revealed that a single base substitution (T–A) was detected in dnrl1, leading to a single amino acid change (L376H) in the coding protein. The mutation led to a lower expression level of DNRL1 as well as the lower activity of DAHPS in the mutant compared with the wild type. Genetic complementation and over-expression of DNRL1 could rescue the narrow-rolled phenotype. DNRL1 was constitutively expressed in all tested organs and exhibited different expression patterns from other narrow-rolled leaf genes. DNRL1-GFP located to chloroplasts. The lower level of chlorophyll in dnrl1 was associated with the downregulation of the genes responsible for chlorophyll biosynthesis and photosynthesis. Furthermore, dnrl1 showed significantly reduced levels of aromatic amino acids including Trp, Phe and Tyr. We conclude that OsDAHPS, encoded by DNRL1, plays a critical role in leaf morphogenesis by mediating the biosynthesis of amino acids in rice.
Highlights
IntroductionAs a densely planted crop, a moderate leaf shape is conducive to maintaining its upright gesture, improving photosynthetic efficiency and increasing rice grain production [1,2]
Rice leaf morphology is critical for light energy capture and conversion efficiency
We conclude that OsDAHPS, encoded by DNRL1, plays a critical role in leaf morphogenesis by modulating the biosynthesis of amino acids
Summary
As a densely planted crop, a moderate leaf shape is conducive to maintaining its upright gesture, improving photosynthetic efficiency and increasing rice grain production [1,2]. A narrow leaf blade helps to maintain an upright gesture and has been proposed as one of the ideal characteristics in rice breeding practice [3]. Narrow leaf mutants are usually accompanied by other phenotypic variations such as rolled leaf, dwarfism, increased tiller number and leaf angle. Based on the information from cloned narrow leaf genes, the molecular mechanisms underlying narrow leaf phenotypes are complicated and mainly associated with microRNAs, transcriptional factors, cellulose enzymes and phytohormones. OsDCL1 encodes a dicer or dicer-like (DCL) protein which is required for the maturation of miRNAs and siRNAs. It has been shown that the weak loss of function OsDCL1 transformants display narrow, rolled, and outward-folded leaves. The sll mutant exhibits extremely incurved leaves due to the defective development of sclerenchymatous cells on the abaxial side [8]
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