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.

Figure 1

A schematic presentation of the five well-studied rice CMS types. Abbreviations for cytoplasm sources are R^WA for wild-abortive Oryza rufipogon, R^RA for red-awned O. rufipogon, and R^W1 for Chinese wild rice (O. rufipogon) accession W1; I^BT and I^LD for indica Boro-II type and Lead rice, respectively. Nucleus sources are either indica (I) or japonica (J).

Figure 2

A schematic presentation of anther and pollen development in wild type (WT) rice, wild-abortive CMS (WA-CMS) rice, temperature- and photoperiod -sensitive genic male sterile (TGMS and PGMS) rice. Stage demarcation and developmental features of WT rice are adopted from Zhang and Wilson ([2009]); those of WA-CMS, TGMS and PGMS are according to Luo et al. ([2013]), Ku et al. ([2003]), and Ding et al. ([2012a]), respectively. Dots represent the DNA fragmentations detected by TUNNEL assay in tapetal cells undergoing programmed cell death. AP, aborted pollen; BP, binucleate pollen; E, epidermis; En, endothecium; ML, middle layer; T, tapetum; MMC, microspore mother cell; MC, meiotic cell; DY, dyad; Td: tetrad; MP, mature pollen.

Figure 3

Planting areas covered by different types of hybrid rice in China (1983–2012). a, Hybrids based on BT-, HL-, and WA-CMS lines as well as EGMS (environment-conditioned genic male sterility). b, Hybrids based on different CMS types with similar features to WA-CMS. For definition of different CMS types see Table 1. Note the data were composed of hybrid rice cultivars that had grown in more than 50,000 ha (1983 to 2012) in this figure, cultivars with less growing area were not included.