Gene expression analysis of light-modulated germination in tomato seeds.

G.A. AUGE; S. PERELMAN; R.A. SÁNCHEZ; J. BOTTO.

Salamanca, España

Workshop; 2nd International Workshop on Molecular Aspects of Seed Dormancy and Germination.; 2007

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Germination of tomato seeds can be inhibited by a long exposure to far-red light (FR). After continuous exposure to FR (FRc), germination can be re-induced by a subsequent red light pulse (Rp). In order to identify new elements participating in the responses to light  and in signal transduction pathways affecting germination through phytochrome A in tomato, a study of gene expression changes was made in wild type cv. Money Maker (MM) and phyA mutant (fri, far-red light  insensitive) tomato seeds under inhibition and re-induction treatments. After 3 hours of dark incubation, all seeds were exposed to FRc for 24 hours. Immediately after the FRc, a group of seeds of each genotype received a Rp (30 minutes) and then continued their incubation in darkness; the other seeds were transferred directly to darkness. Samples were taken at 3, 6, 9, 12, 24, 27, 30 and 51 hours and RNA extracted. The hybridization of RNA samples was done in TIGR with 10K potato cDNA arrays.    The matrix of gene expression values of all treatments was subjected to a rank transformation followed by a correspondence analysis. The multivariate analysis shows that the light treatments have highly significant effects on the expression pattern. In MM seeds, stimulation is the predominant FRc influence on gene expression compared with control seeds (incubated in darkness). Close to 200 genes are up-regulated whereas only 10 genes were repressed.  The Rp after the FRc treatment induces the early expression (3 hours after light pulse) of more than 100 genes and down regulates about the same number. In both cases the number of genes with altered expression increases between 3 (up regulated) and 5 times (down regulated) 24 hours later. A similar pattern is observed in fri seeds when they were compared with the wild type, although the number of genes affected is relatively small. A search of genes with differential expression between light treatments was done with genArise program. Within the group of genes repressed after FRc and re-induced by Rp are SOS2, RNA binding protein-ABA regulated (RBP) and COP9 signalosome subunit 6 (CSN6). On the other hand, some of the genes whose expression is induced under FRc and repressed by Rp are GIGANTEA, Early Light Inducible Protein (ELIP) and PHYB2. In phyA mutant seeds, the expression of several of these genes are not affected by light.  RT-PCR expression analysis of some of those genes will be presented and their relevance discussed.