Quantitative Trait

Mol. Cells, Vol. 24, No. 1, pp. 83-94

Quantitative Trait Loci Associated with Functional Stay-Green

SNU-SG1 in Rice

Soo-Cheul Yoo†, Sung-Hwan Cho†, Haitao Zhang, Hyo-Chung Paik, Chung-Hee Lee, Jinjie Li,

Jeong-Hoon Yoo, Byun-Woo Lee, Hee-Jong Koh, Hak Soo Seo, and Nam-Chon Paek*

Department of Plant Science and Research Institute for Agriculture and Life Sciences, Seoul National University, Seoul 151-921, Korea.

(Received February 4, 2007; Accepted April 9, 2007)

During monocarpic senescence in higher plants, func-

tional stay-green delays leaf yellowing, maintaining pho-

tosynthetic competence, whereas nonfunctional stay-green

retains leaf greenness without sustaining photosynthetic

activity. Thus, functional stay-green is considered a benefi-

cial trait that can increase grain yield in cereal crops. A

stay-green japonica rice ‘SNU-SG1’ had a good seed-

setting rate and grain yield, indicating the presence of a

functional stay-green genotype. SNU-SG1 was crossed

with two regular cultivars to determine the inheritance

mode and identify major QTLs conferring stay-green in

SNU-SG1. For QTL analysis, linkage maps with 100 and

116 DNA marker loci were constructed using selective

genotyping with F2 and RIL (recombinant inbred line)

populations, respectively. Molecular marker-based QTL

analyses with both populations revealed that the functional

stay-green phenotype of SNU-SG1 is regulated by several

major QTLs accounting for a large portion of the genetic

variation. Three main-effect QTLs located on chromo-

somes 7 and 9 were detected in both populations and a

number of epistatic-effect QTLs were also found. The

amount of variation explained by several digenic interac-

tions was larger than that explained by main-effect QTLs.

Two main-effect QTLs on chromosome 9 can be consid-

ered the target loci that most influence the functional stay-

green in SNU-SG1. The functional stay-green QTLs may

help develop low-input high-yielding rice cultivars by

QTL-marker-assisted breeding with SNU-SG1.

Keywords: Epistasis; F2 Population; Functional Stay-

Green; Recombinant Inbred Lines; QTL Mapping; Rice;

Selective Genotyping; SNU-SG1.

† These authors contributed equally to this work.

* To whom correspondence should be addressed.

Tel: 82-2-880-4543; Fax: 82-2-873-2056

E-mail: ncpaek@snu.ac.kr Introduction Leaf greenness depends on the concentration of chloro-

phyll, the most important green pigment absorbing

sunlight energy for photosynthesis. Leaf yellowing gener-

ally results from progressive breakdown of chlorophyll

during senescence. Plants assimilate carbohydrates and

nitrogen in vegetative organs (source) and remobilize

them to newly developing tissues during development, or

to reproductive organs (sink) during senescence. To in-

crease grain yield in cereal crops, source strength must be

increased so that sink organs can be filled via efficient

translocation. Photosynthates generated after heading are

responsible for 60-90% of the total carbon accumulated in

rice panicles at harvest, while 70−90% of total panicle

nitrogen uptake occurs before heading and is subse-

quently remobilized from leaf to grain during monocarpic

senescence (Mae, 1997; Yue et al., 2006). Both persis-

tence of high photosynthetic capacity and efficient nitro-

gen remobilization during grain filling, therefore, have

been considered key factors in increasing grain yield

(Abdelkhalik et al., 2005; Yamaya et al., 2002).

Stay-greenness (or delayed senescence) during the final

stage of leaf development is an important trait in increas-

ing source strength in grain production, and its physio-

logical and genetic bases have been studied in several

plants. Thomas and Howarth (2000) classified five stay-

green phenotypes according to their senescing behaviors.

Stay-green also can be generally divided into two groups,

functional and nonfunctional. Functional stay-green is

defined as retaining both leaf greenness and photosyn-

thetic competence much longer during senescence than

Abbreviations: cM, centiMorgan; DH lines, doubled haploid

lines; LOD, logarithm of odds; PCR, polymerase chain reaction;

PSII, photosystem II; QTL, quantitative trait loci; RFLP, restric-

tion fragment length polymorphism; RIL, recombinant inbred

line; SSD, single seed decent; SSR, simple sequence repeat. MoleculesandCells

©KSMCB 2007