Moderate Salinity Stress Reduces Rice Grain Yield by Influencing Expression of Grain Number- and Grain Filling-Associated Genes

Abstract

Soil salinity is an environmental stress severely impacting on rice grain yield. However, limited information is available on how salinity affects expression levels of genes determining grain yield. In this study, we investigated agronomic traits associated with grain yield among three japonica rice cultivars grown either under moderate salinity with an electrical conductivity of 4 dS/m or under non-saline conditions in a paddy field in Dongying, Shandong, China. Moderate salinity affected rice yield predominantly by reducing grain number and grain filling. We compared expression levels of genes determining grain number in young panicles (0.5–1 cm in length) of plants grown under salinity or non-saline conditions. Transcription of Lax panicle 1, Lax panicle 2, Ideal plant architecture (IPA1), Dense and erect panicle 1, Tawawa 1, and OsMADS1 was significantly repressed, whereas that of Cytokinin oxidase/dehydrogenase, Grain number per panicle 1, and Narrow leaf 1 was not significantly influenced by salinity. OsmicroRNA156, the posttranscriptional regulator of IPA1, was induced by salinity in the panicle and seedlings and complemented the expression patterns of IPA1. This result implied that the OsmicroRNA156–IPA1 pathway was involved in rice salinity responses. The grain filling-associated genes Grain incomplete filling 1, Grain incomplete filling 2, and Nuclear factor Y were down-regulated by salinity in the spikelet at 5 or 10 days after fertilization, which contributed to the salinity-triggered reduction in grain weight. These findings suggest some targets that may be utilized to improve the grain yield under salinity stress conditions via breeding and gene-pyramiding approaches.