A CCR4-associated factor 1, OsCAF1B, confers tolerance of low-temperature stress to rice seedlings.

KEY MESSAGE: Rice is an important crop in the world. However, little is known about rice mRNA deadenylation, which is an important regulation step of gene expression at the post-transcriptional level. The CCR4-NOT1 complex contains two key components, CCR4 and CAF1, which are the main cytoplasmic deadenylases in eukaryotic cells. Expression of OsCAF1B was tightly coupled with low-temperature exposure. In the present study, we investigated the function of OsCAF1B in rice by characterizing the molecular and physiological responses to cold stress in OsCAF1B overexpression lines and dominant-negative mutant lines. Our results demonstrate that OsCAF1B plays an important role in growth and development of rice seedlings at low temperatures. Rice is a tropical and subtropical crop that is sensitive to low temperature, and activates a complex gene regulatory network in response to cold stress. Poly(A) tail shortening, also termed deadenylation, is the rate-limiting step of mRNA degradation in eukaryotic cells. CCR4-associated factor 1 (CAF1) proteins are important enzymes for catalysis of mRNA deadenylation in eukaryotes. In the present study, the role of a rice cold-induced CAF1, OsCAF1B, in adaptation of rice plants to low-temperature stress was investigated. Expression of OsCAF1B was closely linked with low-temperature exposure. The increased survival percentage and reduced electrolyte leakage exhibited by OsCAF1B overexpression transgenic lines subjected to cold stress indicate that OsCAF1B plays a positive role in rice growth under low ambient temperature. The enhancement of cold tolerance by OsCAF1B in transgenic rice seedlings involved OsCAF1B deadenylase gene expression, and was associated with elevated expression of late-response cold-related transcription factor genes. In addition, the expression level of OsCAF1B was higher in a cold-tolerant japonica rice cultivar than in a cold-sensitive indica rice cultivar. The results reveal a hitherto undiscovered function of OsCAF1B deadenylase gene expression, which is required for adaptation to cold stress in rice.

A CCR4 Association Factor 1, OsCAF1B, Participates in the αAmy3 mRNA Poly(A) Tail Shortening and Plays a Role in Germination and Seedling Growth.

Poly(A) tail (PAT) shortening, also termed deadenylation, is the rate-limiting step of mRNA degradation in eukaryotic cells. The carbon catabolite repressor 4-associated factor 1s (CAF1s) were shown to be one of the major enzymes for catalyzing mRNA deadenylation in yeast and mammalian cells. However, the functions of CAF1 proteins in plants are poorly understood. Herein, a sugar-upregulated CAF1 gene, OsCAF1B, is investigated in rice. Using gain-of-function and dominant-negative mutation analysis, we show that overexpression of OsCAF1B resulted in an accelerated α-amylase gene (αAmy3) mRNA degradation phenomenon, while ectopic expression of a form of OsCAF1B that had lost its deadenylase activity resulted in a delayed αAmy3 mRNA degradation phenomenon in transgenic rice cells. The change in αAmy3 mRNA degradation in transgenic rice is associated with the altered lengths of the αAmy3 mRNA PAT, indicating that OsCAF1B acts as a negative regulator of αAmy3 mRNA stability in rice. Additionally, we found that overexpression of OsCAF1B retards seed germination and seedling growth. These findings indicate that OsCAF1B participates in sugar-induced αAmy3 mRNA degradation and deadenylation and acts a negative factor for germination and seedling development.