MicroRNA Regulation of Abiotic Stress Response in 7B-1 Male-Sterile Tomato Mutant

The 7B-1 tomato (Solanum lycopersicum L. 'Rutgers') is a male-sterile mutant with enhanced tolerance to abiotic stress in a blue-light (BL) specific manner compared with its wild-type (WT). This makes the 7B-1 a potential candidate for hybrid seed breeding and stress engineering. To identify small RNAs (sRNAs) linked to stress tolerance of 7B-1, two sRNA libraries from BL-grown 7B-1 and WT seedlings treated simultaneously with abscisic acid (ABA) and mannitol were sequenced, and sRNA profiles were compared. Twenty nine families of known microRNAs (miRNAs) and 27 putative novel miRNAs were identified from the two libraries. MiR5300, miR5301, miR2916, and a novel miRNA denoted miR#C were upregulated, while miR159, miR166, miR472, miR482, and two novel miRNAs, miR#A and miR#D, were downregulated in stress-treated 7B-1 seedlings. MiRNA targets with potential roles in stress regulation were validated by rapid amplification of 5' complementary DNA ends (5'-RACE) analysis. Expression of miR159, miR166, miR472, miR482, miR#A, and miR#D together with their targets were further investigated in response to ABA, mannitol, NaCl, and cold treatments and a strong negative correlation was observed between the levels of these miRNAs and expression of their targets. Only miR159 and miR166 responded to cold treatment. MiR#A and its target were regulated by ABA and mannitol as early as 0.5 h after the treatments, while other miRNAs and targets were regulated only after 2 h. This suggests a role in early response to stress for miR#A. Our data suggests that miR159, miR166, miR472, miR482, miR#A, and miR#D are likely to facilitate the BL-specific enhanced tolerance of 7B-1 to abiotic stress.