The Molecular Basis of Cold-Induced Pollen Sterility in Rice

Although originally a tropical plant, an increasing amount of rice is grown in temperate climate zones of the world. Rice yields in most temperate climate zones are variable and yield losses due to coldinduced pollen sterility (CIPS) are the main contributor to this variation. The problem of CIPS is therefore a major bottleneck for the further improvement of rice yields in those areas. The growing season in temperate climate zones is shorter, confronting rice crops with colder conditions both at the start and end of the season. Cold spells at the reproductive stage are most damaging and an estimated 7 million ha world-wide are prone to this damage (Sthapit and Witcombe, 1998). In Australia, cool temperatures during the early booting stage cause an average yield reduction of 5–10% annually ($A44 million), with cold snaps occurring on average every 3–4 years causing severe yield losses of 20–40% (Jacobs and Pearson, 1994, 1999). Breeding efforts to produce cold-tolerant rice cultivars have focused on improving seedling vigor, shortening the growth season, and improving cold-tolerance at the booting stage (Andaya and Mackill, 2003a, b). Breeding for cold tolerance has traditionally been difficult due to the unpredictability and variability of the weather (timing and severity are beyond control) and due to complex interactions between cold sensitivity and environmental factors (lighting, nutrition). Clearly, breeding for cold tolerant rice would benefit from a better understanding of the underlying molecular mechanism and the development of molecular markers.