Characterization and Use of Male Sterility in Hybrid Rice Breeding

Abstract

The hybrid rice (Oryza sativa L.) breeding that was initiated in China in the 1970s led to a great improvement in rice productivity. In general, it increases the grain yield by over 20% to the inbred rice varieties, and now hybrid rice has been widely introduced into Africa, Southern Asia and America. These hybrid varieties are generated through either three-line hybrid and two-line hybrid systems; the former is derived from cytoplasmic male sterility (CMS) and the latter derived from genic male sterility (GMS). There are three major types of CMS (HL, BT and WA) and two types of GMS (photoperiod-sensitive (PGMS) and temperature-sensitive (TGMS)). The BT-and HL-type CMS genes are characterized as orf79 and orfH79, which are chimeric toxic genes derived from mitochondrial rearrangement. Rf3 for CMS-WA is located on chromosome 1, while Rf1, Rf4, Rf5 and Rf6 correspond to CMS-BT, CMS-WA and CMS-HL, located on chromosome 10. The Rf1 gene for BT-CMS has been cloned recently, and encodes a mitochondriatargeted PPR protein. PGMS is thought to be controlled by two recessive loci on chromosomes 7 and 12, whereas nine recessive alleles have been identified for TGMS and mapped on different chromosomes. Attention is still urgently needed to resolve the molecular complexity of male sterility to assist rice breeding.Key words: hybrid rice; male sterility; Oryza sativa.Li SQ, Yang DC, Zhu YG (2007). Characterization and use of male sterility in hybrid rice breeding. J. Integr. Plant Biol. 49(6), 791−804. Available online at www.blackwell-synergy.com/links/toc/jipb, www.jipb.netAs one of the most ancient grain crops, rice is a staple food for people due to it being high in carbohydrates, low in fat, and rich in proteins, vitamins and minerals. It has been used as a major food for over ten thousand years. It has been cultivated in 113 countries. It is estimated that half of the world's population subsists wholly or partially on rice. In 2001, about 517.9 thousand million kg out of 580 thousand million kg rice were directly consumed as foods around the world. Although about 90 percent of rice is grown and consumed in Asia, the quantity of rice consumption in Sub-Sahara Africa has doubled in the last two decades (FAOSTAT) from about 8.2 thousand million kg of paddy rice in 1980 to 16.7 thousand million kg in 2000. The rapid increase of rice consumption is mainly due to the expansion of human population in the developing countries. It is predicted that the population in the world will increase continually from the current 6 billion to 8 billion in 2030. According to documents from FAOSTAT, the annual loss of land for other uses is estimated to be about 10 to 35 million hm 2 /year, half of this coming from cropland. Facing the challenge of population growth and cropland reduction, it is obvious that the only way to solve this problem is to improve the yield of cereal crops namely, rice, wheat and corn etc. (Yuan and Peng 2005). Fortunately, the importance of rice to feed the population of the world is recognized by the Uni...

A Reevaluation of Rice Mitochondrial Evolution Based on the Complete Sequence of Male-Fertile and Male-Sterile Mitochondrial Genomes

“…This is an unanticipated result, given that WA-CMS is thought to have originated from the O. rufipogon/Oryza nivara complex, the ancestor of cultivated rice in Asia (Li et al, 2005). Nevertheless, the WA-CMS lines have been developed from crosses between wild rice or traditional rice varieties (O. nivara, O. rufipogon, Oryza glaberrima, and O. sativa indica) as a maternal parent and earlymatured indica rice varieties (such as Zhen-Shan 97) as the recurrent paternal lines (Li et al, 2007). Therefore, it is possible that N and WA-CMS mitochondrial genomes originate from the same species, O. sativa indica, explaining their observed low nucleotide substitution rate.…”

“…One mitochondrial genome comes from a maintainer line and is referred to as normal (N), while the other carries the wild abortive CMS and is hereafter referred to WA-CMS. There are over 60 types of rice CMS lines that can be categorized into three types, namely wild-abortive (WA) type, Honglian (HL) type, and Boro II (BT) type, based on their inheritance, morphology of abortive pollen, and identity of the fertility-restorer genes (for review, see Li et al, 2007). About 90% of the three-line hybrid rice in China is composed of hybrids derived from the WA-CMS lines.…”

Pentatricopeptide-repeat family protein RF6 functions with hexokinase 6 to rescue rice cytoplasmic male sterility

“…The pollen of these plants aborts at the trinucleate stage and can be suppressed by Rf1A and Rf1B (26). For HL-CMS, pollen aborts at the dinucleate stage and exhibits a spherical shape and negative staining with iodine-potassium iodide (I 2 -KI) solution (20). The HL-CMS trait is associated with orfH79, a chimeric mitochondrial gene located downstream of atp6.…”

“…Rice CMS is categorized into three major types: Wild Abortive (WA), originating from a wild abortive rice line; Honglian (HL), originating from red-awned wild rice; and BT, originating from ChinsurahBoro II rice (20). These three types of CMS contribute to ∼60% of the global hybrid rice production (21,22).…”

Alterations of Mitochondrial Protein Assembly and Jasmonic Acid Biosynthesis Pathway in Honglian (HL)-type Cytoplasmic Male Sterility Rice

“…These CMS lines have differences in inheritance, morphology of abortive pollens, and restoration-maintenance relationships (9). HL CMS rice was developed by backcrossing red-awned wild rice (Oryza rufipogon) with the indica variety Lian Tang-Zao in Hainan China in the 1970s.…”