Expression patterns of auxin-responsive genes during tomato flower pedicel abscission and potential effects of calcium

This study aimed to determine the expression patterns of auxin (Aux/IAA)-responsive genes (ARG) during tomato flower pedicel abscission and the role of calcium in this auxin-mediated abscission. Most of the 19 proteins encoded by SlIAA genes showed the presence of all four conserved domains (I, II, III and IV). Expressions of some SlIAA genes decreased significantly (SlIAA 1, 3, 5, 8, 9, 10, 16, 17 and 27), while others increased (SlIAA 2, 4, 6, 7, 11, 12, 13, 26 and 29) at 0.5 h after excision. Most SlIAA genes were significantly upregulated at 1 h (except 9 and 27) then decreased to relatively low levels until 4 h after excision (except 4, 5, 8, 12, 14, 26 and 29). The SIAA genes were analysed and screened based on their expression patterns during different abscission phases. SlIAA4, 6, 9, 12 and 27 had relatively high expression levels consistent with the abscission rate, indicating potential roles in mediating abscission. SlIAA2, 3, 4, 5, 7, 9, 12, 13, 14, 16, 17, 26, 27 and 29 may have been important in delaying abscission, while SlIAA1, 9 and 12 may have been required for the completion of ethylene-induced abscission. SlIAA4, 6, 7, 8, 14, 16, 17 and 29 were important in calcium-delayed abscission. Analysis of other ARG revealed that tomato GH3 may have acted as an effective negative regulator in IAA-induced delay in abscission, while small auxin-up RNA expression patterns indicated that it may be a marker of IAA level throughout the abscission process.