Suppression of LX Ribonuclease in Tomato Results in a Delay of Leaf Senescence and Abscission

Although present in different organisms and conserved in their protein sequence, the biological functions of T2 ribonucleases (RNase) are generally unknown. Tomato (Lycopersicon esculentum) LX is a T2/S-like RNase and its expression is known to be associated with phosphate starvation, ethylene responses, and senescence and programmed cell death. In this study, LX function was investigated using antisense tomato plants in which the LX protein level was reduced. LX protein levels normally become elevated when leaves senesce and antisense inhibition of LX retarded the progression of senescence. Moreover, we observed a marked delay of leaf abscission in LX-deficient plants. This correlated with specific induction of LX protein in the tomato mature abscission zone tissue. LX RNase gene regulation and the consequences of antisense inhibition indicate that LX has an important functional role in both abscission and senescence

Histochemical staining of GUS activity in vascular tissues of and tomato

(A seedling, 4 d after germination. (B Young rosette leaves of , 13 d after germination. (C, D. Cross-sections of young (C) and mature (D) inflorescence stems. (E) root vascular tissues. (F Cross-section of tomato stem, counter-stained with safranin.<p><b>Copyright information:</b></p><p>Taken from "Expression analysis of the nuclease gene promoter during senescence, abscission, and programmed cell death-related processes"</p><p></p><p>Journal of Experimental Botany 2008;59(12):3247-3258.</p><p>Published online 4 Jul 2008</p><p>PMCID:PMC2529240.</p><p></p

Histochemical staining of GUS activity in floral organs and tomato fruit

(A) anther. (B) Silique after pollination. (C) Young silique showing the developing seeds. (D) Cross-section of green tomato. (E) Magnification of one of the seeds.<p><b>Copyright information:</b></p><p>Taken from "Expression analysis of the nuclease gene promoter during senescence, abscission, and programmed cell death-related processes"</p><p></p><p>Journal of Experimental Botany 2008;59(12):3247-3258.</p><p>Published online 4 Jul 2008</p><p>PMCID:PMC2529240.</p><p></p

Histochemical staining of GUS activity in the abscission zones (AZs) of floral organs

(A) petal AZ. (B) Stamen AZ.<p><b>Copyright information:</b></p><p>Taken from "Expression analysis of the nuclease gene promoter during senescence, abscission, and programmed cell death-related processes"</p><p></p><p>Journal of Experimental Botany 2008;59(12):3247-3258.</p><p>Published online 4 Jul 2008</p><p>PMCID:PMC2529240.</p><p></p

Microarray Analysis of the Abscission-Related Transcriptome in the Tomato Flower Abscission Zone in Response to Auxin Depletion1[C][W][OA]

The abscission process is initiated by changes in the auxin gradient across the abscission zone (AZ) and is triggered by ethylene. Although changes in gene expression have been correlated with the ethylene-mediated execution of abscission, there is almost no information on the molecular and biochemical basis of the increased AZ sensitivity to ethylene. We examined transcriptome changes in the tomato (Solanum lycopersicum ‘Shiran 1335’) flower AZ during the rapid acquisition of ethylene sensitivity following flower removal, which depletes the AZ from auxin, with or without preexposure to 1-methylcyclopropene or application of indole-3-acetic acid after flower removal. Microarray analysis using the Affymetrix Tomato GeneChip revealed changes in expression, occurring prior to and during pedicel abscission, of many genes with possible regulatory functions. They included a range of auxin- and ethylene-related transcription factors, other transcription factors and regulatory genes that are transiently induced early, 2 h after flower removal, and a set of novel AZ-specific genes. All gene expressions initiated by flower removal and leading to pedicel abscission were inhibited by indole-3-acetic acid application, while 1-methylcyclopropene pretreatment inhibited only the ethylene-induced expressions, including those induced by wound-associated ethylene signals. These results confirm our hypothesis that acquisition of ethylene sensitivity in the AZ is associated with altered expression of auxin-regulated genes resulting from auxin depletion. Our results shed light on the regulatory control of abscission at the molecular level and further expand our knowledge of auxin-ethylene cross talk during the initial controlling stages of the process

Identification of defense-related genes newly associated with tomato flower abscission

The current abscission model suggests the formation of a post-abscission trans-differentiation of a protective layer as the last step of the process. The present report expands the repertoire of genes activated in the tomato flower abscission zone (AZ), which are likely to be involved in defense responses. We identified four different defense-related genes, including: Cysteine-type endopeptidase, α-Dioxygenase 1 (α-DOX1), HopW1-1-Interacting protein2 (WIN2) and Stomatal-derived factor-2 (SDF2), that are newly-associated with the late stage of the abscission process. The late expression of these genes, induced at 8–14 h after flower removal when pedicel abscission was already in progress, was AZ-specific, and was inhibited by treatments that prevented pedicel abscission, including 1-methylcyclopropene pretreatment or IAA application. This information supports the activation of different defense responses and strategies at the late abscission stages, which may enable efficient protection of the exposed tissue toward different environmental stresses

Programmed Cell Death Occurs Asymmetrically during Abscission in Tomato[C][W][OA]

This work examines abscission in tomato and finds that it is associated with programmed cell death and expression of the RNase LX, both of which occur on the distal side of the abscission zone, indicating asymmetric processes occurring during abscission