Phenotypic analyses of rice lse2 and lse3 mutants that exhibit hyperaccumulation of starch in the leaf blades.

Chenggang Liang,Tian Li,Ryu Ohsugi,Masaki Okamura,Rei Tanimoto,Tatsuro Hirose,Tomio Terao,Akio Miyao,Hirohiko Hirochika,Naohiro Aoki

doi:10.1186/s12284-014-0032-3

Abstract

BackgroundTo identify genes that potentially regulate the accumulation, mobilization, and transport of photoassimilates in rice (Oryza sativa L.) leaves, we recently screened a mutant collection of rice by iodine staining to visualize leaf starch contents. From this screening, we isolated a rice mutant that exhibits hyperaccumulation of starch in leaves and designated it as the Leaf Starch Excess 1 (LSE1) mutant. Here, we report two other rice LSE mutants, LSE2 and LSE3.ResultsUnlike lse1 plants, lse2 and lse3 plants displayed retarded growth; lse2 showed an extremely dwarf phenotype and rarely survived in paddy fields; lse3 showed inhibited growth with pale green leaf blades, low tiller numbers, reduced height, and low grain yield. In lse2 and lse3 plants, the mature source leaves contained larger amounts of starch and sucrose than those in wild-type and lse1 plants. Furthermore, microscopic observations of leaf transverse sections indicated that hyperaccumulation of starch in chloroplasts of mesophyll and bundle sheath cells occurred in lse2 and lse3 plants, while that in vascular cells was noticeable only in lse3 leaves.ConclusionsThe distinct phenotypes of these three LSE mutants suggest that the LSE2 and LSE3 mutations occur because of disruption of novel genes that might be involved in the path of sucrose transport from mesophyll cells to phloem sieve elements in rice leaves, the mechanism for which has not yet been elucidated.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-014-0032-3) contains supplementary material, which is available to authorized users.

Highlights

To identify genes that potentially regulate the accumulation, mobilization, and transport of photoassimilates in rice (Oryza sativa L.) leaves, we recently screened a mutant collection of rice by iodine staining to visualize leaf starch contents
Similar to Leaf Starch Excess 1 (LSE1), the stain-positive phenotype in LSE2 was segregated at a ratio of 0.22, suggesting that the phenotype was due to a recessive mutation of a single gene
Leaf Starch Excess (LSE) mutationa Number of stain-positive plants Number of stain-negative plants Segregation ratio of stain-positive plants P-Valueb aHeterozygously mutated lines were used for this analysis; 109, 165, and 78 seedlings of LSE1, LSE2, and LSE3, respectively, were subjected to iodine staining. bProbability calculated by χ2-test when the hypothetical segregation ratio of stain-positive plants is 0.25

Summary

Introduction

To identify genes that potentially regulate the accumulation, mobilization, and transport of photoassimilates in rice (Oryza sativa L.) leaves, we recently screened a mutant collection of rice by iodine staining to visualize leaf starch contents. Mutants lacking function in genes that are involved in these metabolic processes often display ‘starch excess (sex)’ phenotypes that accumulate excess quantities of starch in the leaves Since these phenotypes can be screened by iodine staining of mature leaves, the genes responsible for sex mutations have been extensively studied to explore the molecular mechanisms of carbohydrate partitioning in leaves. We recently reported a sex mutant by an iodine staining-based screening of a rice mutant collection (Hirose et al 2013) Seedlings of this mutant accumulated excess starch in the leaf blades, and the mutant was designated Leaf Starch Excess 1 (LSE1). Larsen (Vriet et al 2010)

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