| The abscission of organs is a very widespread phenomena in nature, it is the result of long-term adaptation of plants to the environment. Although abscission has a favorable side to agricultural production, it is unfavorable in most case. For example, flower and fruit dropping in tomato and other crops uaually reduces the yield seriously and brings great loss. It is proved that IAA and calcium could inhibit abscission of plant organs, this role of IAA is achieved by auxin-responsive gene Aux/IAA, but the mechanism of calcium in mediating abscission is less clear. This paper analyses the informatics of tomato Aux/IAA gene, and identified the SlIAA which is related to IAA in abscission zone (AZ) of tomato pedicel, and investigates further the role of calcium in mediating SlIAA gene expression in tomato pedicel AZ. Thereby we discuss the relationship between the inhibition of calcium to tomato pedicel abscission and the regulation of calcium on SlIAA expression to lay the theoretical basis for expliciting the mechanism of calcium on tomato pedicel abscission. The main results are as follows:1.19 SlIAA genes are identified through the information analysis of tomato Aux/IAA gene family, and most of them have four conserved domains (â… ,â…¡,â…¢,â…£), and they are classified into five subfamilies. Phylogenetic analyses reveal that the inherited distance are close between SlIAA1,3,4,9,14,16,27 and other known abscission-related genes, so they may be associated with the abscission of tomato pedicel; And the homology of SlIAA7,10,14, 16,17 and TaIAA1 which was regulated by calcium is relatively high, so they also may be regulated by calcium.2. The research about IAA induction suggests:it is not required that the synthesis of proteins for IAA induction to five SlIAAs (SlIAA1,2,3,16 and 27), so they belong to early auxin-responsive genes; Fourteen SlIAAs (SlIAA4,5,6,7,8,9,10,11,12,13,14,17,26 and 29) represent the opposite result, so they may be late auxin-responsive genes.3. IAA and calcium inhibit the abscission of tomato pedicel explants, Vp induces abscission. At the same time, the expression of SlIAA4,6,9,12 and 27 raise consistent with the complete abscission during the natural abscission, indicating their important roles in mediating the completion of natural abscission.4. During the abscission of tomato pedicel, IAA induces most SlIAAs expression. Among of them, SlIAA2,3,4,5,7,9,12,13,14,16,17,26,27 and 29 may be important factors in IAA-delayed abscission; Calcium accelerates SlIAA4,6,7,8,14,16,17 and 29 expression in abscission prophase (before 16 h), so they may be key genes in calcium-delayed abscission.The further study about the regulation role of calcium on the key genes suggests, when the endogenous IAA is depleted, the treatment of calcium for 1 h induces the expression of SlIAA4,6,7,8,16 and 29, and the induction is relative to calcium concentration, representing low concentration induced, high concentration inhibited; but calcium treatment for 16 h inhibits mainly the expression. Calcium promotes the induction of IAA to SlIAA through CaM. 5. The similar expression pattern of SAUR with calcium and IAA treatments implies that calcium may participate in the auxin response by the regulation of SAUR expression. The expression of GH3 is enhanced in the late abscission phases, the result suggests that GH3 genes may be a negative regulators of abscission.6. The expression rule of SlIAA genesis weak with Vp treatment, but the expression of SlIAA1,5,9,13 and 27 enhance at 32 h, it implies that they may be required in the completion of Vp-promoted abscission. When the the endogenous IAA is depleted, Vp induces the expression of SlIAA8 and 11, and the induction depends on CaM.8. For all the test results, we speculate that calcium may be concerned with IAA signal transduction and induce SlIAA expression to inhibit abscission. SlIAA4,16 and 29 may be the key factors which affect the speed of abscission. However, it remains to be verified further by transgenosis.
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