2011 Annual Report
1a.Objectives (from AD-416)
The long-term objective of this project is to develop improved rice (Oryza sativa L.) germplasm for use in breeding elite varieties adapted to temperate environments by identifying, characterizing, and manipulating genes that affect crop productivity. In temperate regions, seedling cold tolerance in rice is important for successful stand establishment and plant development, both of which directly impact yield. Over the next five years, two major objectives will be addressed:.
1)the molecular genetic basis of rice seedling cold tolerance conferred by the major quantitative trait loci qCTS12 and qCTS4 will be determined and.
2)the information obtained from the analysis of qCTS12 and qCTS4 will be used to evaluate currently available germplasm and to develop new germplasm with enhanced cold tolerance. qCTS12 and qCTS4 have been fine mapped to regions containing a small number of genes.
1b.Approach (from AD-416)
During this project, the genes that confer cold tolerance will be identified through transformation and candidate gene analysis experiments. The genes and the proteins they encode will be characterized at the molecular level and their effect under field conditions will be determined. The utility of this of this information for evaluating other rice germplasm and for developing efficient approaches to identifying novel sources of cold tolerance will be examined. New germplasm for breeding will be developed by transferring the qCTS12 and qCTS4 genes through conventional and molecular breeding approaches. In addition to providing tools and resources for germplasm improvement, genetic dissection of qCTS12 and qCTS4 will contribute to our fundamental understanding of cold tolerance in rice.
During FY2011, work on genetic characterization of rice seedling cold tolerance, which contributes to grain yield and quality, continued. Transgenic rice plants containing constructs for constitutive expression of the two glutathione S-transferase zeta genes (OsGSTZ1 and.
2)from the cold tolerant variety M-202 were obtained and are undergoing preliminary characterization (i.e. confirmation of transgene expression, assessment of response to cold treatment). Our studies to date indicate that OsGSTZ2 underlies qCTS12, one of the major seedling cold tolerance quantitative trait loci we are characterizing. Transformation of the OsGSTZ2 gene from the susceptible variety IR50 was not successful and is currently being repeated. In addition, near-isogenic line development was continued. An advanced backcross line (6885-2-2), containing both qCTS12 and qCTS4 from M-202, was used to pollinate the cold susceptible variety IR50. Marker analysis conducted this year indicates the crosses were successful and seeds have been harvested and are being screened to identify lines which carry each QTL independently. These near-isogenic lines will facilitate assessment of the individual contribution of each locus to seedling cold tolerance in controlled and field environments. A second year of field trials of advanced backcross lines (including 6885-2-2) was initiated and will be completed during FY2012. Work continues on characterizing additional germplasm as potential sources of improved cold tolerance. This work includes alternative phenotypic assessments of seedling cold tolerance and evaluation of physiological parameters. Germplasm are also being screened with molecular markers derived from qCTS12 candidate gene and linked to the qCTS4 locus. Crosses are being made between germplasm identified as having better tolerance than the California variety M-202, our tolerant check.
Evaluation of alternative indicators of seedling cold tolerance in rice. Seedling cold tolerance in rice is typically assessed using a visual rating scale which can be very subjective, particularly when screening diverse germplasm. A comparison of visual ratings and quantitative indicators of physiological changes in cold-stressed rice seedlings was performed by ARS scientists at Davis, CA, and alternative methods for assessing tolerance were identified. This work will facilitate more accurate and uniform assessment of this important trait from diverse genetic materials. Identification of new sources of cold tolerance will enable improvements in U.S. rice varieties.
Kim, S., Tai, T. 2011. Evaluation of seedling cold tolerance in rice cultivars: a comparison of visual ratings and quantitative indicators of physiological changes. Euphytica. 178:437-447.
Kim, S., Andaya, V., Tai, T. 2011. Cold sensitivity in rice (Oryza sativa L.) is strongly correlated with a naturally occurring I99V mutation in the multifunctional glutathione transferase isoenzyme GSTZ2. Biochemical Journal. 435:373-380.