Workable male sterility systems for hybrid rice: Genetics, biochemistry, molecular biology, and utilization

Abstract

The exploitation of male sterility systems has enabled the commercialization of heterosis in rice, with greatly increased yield and total production of this major staple food crop. Hybrid rice, which was adopted in the 1970s, now covers nearly 13.6 million hectares each year in China alone. Various types of cytoplasmic male sterility (CMS) and environment-conditioned genic male sterility (EGMS) systems have been applied in hybrid rice production. In this paper, recent advances in genetics, biochemistry, and molecular biology are reviewed with an emphasis on major male sterility systems in rice: five CMS systems, i.e., BT-, HL-, WA-, LD- and CW- CMS, and two EGMS systems, i.e., photoperiod- and temperature-sensitive genic male sterility (P/TGMS). The interaction of chimeric mitochondrial genes with nuclear genes causes CMS, which may be restored by restorer of fertility (Rf) genes. The PGMS, on the other hand, is conditioned by a non-coding RNA gene. A survey of the various CMS and EGMS lines used in hybrid rice production over the past three decades shows that the two-line system utilizing EGMS lines is playing a steadily larger role and TGMS lines predominate the current two-line system for hybrid rice production. The findings and experience gained during development and application of, and research on male sterility in rice not only advanced our understanding but also shed light on applications to other crops.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-014-0013-6) contains supplementary material, which is available to authorized users.

Construction of a male sterility system for hybrid rice breeding and seed production using a nuclear male sterility gene

“…PTGMS rice was first adopted for farming in 1995, and its planting area quickly increased and almost covered 20% of rice fields in China by 2012 (1,3). In fact, the highest yielding varieties currently cultivated in China are mostly PTGMS hybrids (1,3). Nonetheless, the PTGMS system also has intrinsic problems primarily in that its fertility is regulated by environmental conditions (5).…”

“…Because PTGMS traits are controlled by nuclear recessive genes and male fertility can be restored by any normal rice cultivars (5-8), broader genetic resources can be explored for strong heterosis (1,5). PTGMS rice was first adopted for farming in 1995, and its planting area quickly increased and almost covered 20% of rice fields in China by 2012 (1,3). In fact, the highest yielding varieties currently cultivated in China are mostly PTGMS hybrids (1,3).…”

“…Defects in any of these events can lead to male sterility. More than 40 nuclear genes required for male fertility have been identified in rice (3,9,10), but these genes have not been tapped for hybrid production because of the inability to propagate pure male sterile seeds on a production scale. Here we isolated a nuclear gene, Oryza sativa No Pollen 1 (OsNP1), essential for pollen development and male fertility in rice.…”

“…CMS is correlated to aberrant, often chimeric, mitochondrial genes absent in maintainer lines, and the male sterility can be suppressed by Rf genes in restorer lines (2). CMS hybrid varieties have been deployed for commercial production since the 1970s and covered ∼40% of rice growing areas in China in 2012 (3). Despite the wide application, CMS systems suffer from several intrinsic problems, including the narrow germplasm resources of restorer lines, the poor genetic diversity between the CMS lines and restorer lines, the instability of male sterility under certain weather conditions, the negative impact of aberrant mitochondrial genes on hybrid performance, and the difficulty to breed new traits into the parental lines (1,3,4).…”

“…CMS hybrid varieties have been deployed for commercial production since the 1970s and covered ∼40% of rice growing areas in China in 2012 (3). Despite the wide application, CMS systems suffer from several intrinsic problems, including the narrow germplasm resources of restorer lines, the poor genetic diversity between the CMS lines and restorer lines, the instability of male sterility under certain weather conditions, the negative impact of aberrant mitochondrial genes on hybrid performance, and the difficulty to breed new traits into the parental lines (1,3,4). These problems limit further improvement in CMS hybrid breeding, which is believed to be the reason that CMS varieties reached a yield plateau in the last 20 y (1, 3).…”