Female sterile tobacco plants are produced by stigma-specific cell ablation.

Abstract

We identified a tobacco stigma‐specific gene, designated STIG1. The STIG1 gene is developmentally regulated and expressed specifically in the stigmatic secretory zone. We used a chimeric STIG1‐GUS gene to show that the stigma‐specific STIG1 gene expression pattern is controlled primarily at the transcriptional level. We constructed a stigma‐specific cytotoxic gene by fusing the STIG1 gene 5′ regulatory region with the coding sequence of the Bacillus amyloliquefaciens barnase gene, to assess the role of the stigmatic secretory zone in the pollination process. Pistils of transgenic STIG1‐barnase tobacco plants undergo normal development, but lack the stigmatic secretory zone and are female sterile. Pollen grains germinate on the ablated ‘stigmatic’ surface, but are unable to penetrate the transmitting tissue of the style. Application of stigmatic exudate from wild‐type pistils to the ablated surface increases the efficiency of pollen tube germination and growth and restores the capacity of pollen tubes to penetrate the style. Our data demonstrate the importance of the stigmatic secretory zone in the pollination process and provide an approach to identify compounds produced by the stigma that are critical for successful pollination and fertilization to occur.

Pollen and Stigma Structure and Function: The Role of Diversity in Pollination

“…Mutations that eliminate this secreted matrix cause female sterility; this defect can be bypassed by adding exogenous lipids (Goldman et al, 1994;Wolters-Arts et al, 1998). The addition of cis-unsaturated triacylglycerides is sufficient for hydration and germination, even on stigmaless tobacco plants .…”

Arabidopsis GRI is involved in the regulation of cell death induced by extracellular ROS

“…S2 A). The STIG1 domain indicates that GRI is related to tobacco and petunia stigma-specific protein, STIG1 (14,15). The tobacco Stig1 encodes a small secreted protein present in the stigmatic lipid exudates.…”

“…S3). Infiltration of leaves with the exogenous superoxide producing system xanthine and xanthine oxidase (X/XO), which enzymatically generates superoxide in the extracellular space (14), caused increased cell death in the gri mutant (Fig. 2E).…”

“…The GRIM REAPER (GRI) protein is an Arabidopsis ortholog of the tobacco stigma-specific protein 1 (STIG1) (14). STIG1 helps to regulate exudate secretion in the pistils of petunia and tobacco (15).…”

Stigma development in Nicotiana tabacum. Cell death in transgenic plants as a marker to follow cell fate at high resolution

“…Stigmas are classified as "wet" when at the receptive stage the surface is covered with a sticky exudate secret ed by the cells of the secretory zone (Cresti et al 1986;Dumas 1977;Dumas et al 1978;Heslop-Harrison and Shivanna 1977;Knox 1984;Mackenzie et al 1990). We studied pistil development in transgenic tobacco plants in which the stigma is ablated by expression of a stigmaspecific cytotoxic gene, STIG /-barnase (Goldman et al 1994). These plants offer a tool to investigate the process of differentiation of the secretory zone.…”