An endochitinase gene expressed at high levels in the stylar transmitting tissue of tomatoes

Transcriptomic Analysis Reveals New Insights into High-Temperature-Dependent Glume-Unclosing in an Elite Rice Male Sterile Line

Glume-unclosing after anthesis is a widespread phenomenon in hybrid rice and also a maternal hereditary trait. The character of Glume-unclosing in rice male sterile lines also seriously influences germination rate and the commercial quality of hybrid rice seeds. We validated that the type of glume-unclosing after anthesis in the elite rice thermo-sensitive genic male sterile (TGMS) line RGD-7S was caused by high temperature. Transcriptomic sequencing of rice panicles was performed to explore the change of transcript profiles under four conditions: pre- and post-anthesis under high temperature (HRGD0 and HRGD1), and pre- and post-anthesis under low temperature (LRGD0 and LRGD1). We identified a total of 14,540 differentially expressed genes (DEGs) including some heat shock factors (HSFs) across the four samples. We found that more genes were up-regulated than down-regulated in the sample pair HRGD1vsHRGD0. These up-regulated genes were significantly enriched in the three biological processes of carbohydrate metabolism, response to water and cell wall macromolecular metabolism. Simultaneously, we also found that the HSF gene OsHsfB1 was specially up-regulated in HRGD1vsHRGD0. However, the down-regulated DEGs in LRGD1vsLRGD0 were remarkably clustered in the biological process of carbohydrate metabolism. This suggests that carbohydrate metabolism may play a key role in regulation of glume-unclosing under high temperature in RGD-7S. We also analyzed the expression pattern of genes enriched in carbohydrate metabolism and several HSF genes under different conditions and provide new insights into the cause of rice glume-unclosing.

Conservation of the role of INNER NO OUTER in development of unitegmic ovules of the Solanaceae despite a divergence in protein function

BACKGROUND

The INNER NO OUTER (INO) gene is expressed in the outermost cell layer of the outer integument of bitegmic ovules and is essential for this organ's growth. The role and cross-species functional conservation of INO orthologs were examined in members of the Solanaceae, which have unitegmic ovules. Unitegmy has evolved several times in disparate angiosperm lineages. INO expression has been observed in the outermost cell layers of all examined unitegmic ovules, but the functional role of INO in unitegmic ovules has not previously been evaluated.

RESULTS

INO orthologs were unambiguously identified in tobacco and tomato by sequence homology. Expression of the tomato INO gene was limited to the outer cell layer of the single integument indicating that this single integument has properties of the outer integument. Expression occurred only after integument initiation, later than observed in ovules of other examined angiosperms. Virus-induced knock-down of expression of the INO ortholog in tobacco inhibited growth of the outer cell layer of the integument leading to a decrease in both integument extension and curvature of the ovule. The altered ovules closely resemble those of the aberrant testa shape (ats) ino mutant combination in Arabidopsis where we see the effect of the ino mutation on a single fused integument produced by the ats mutation. Despite significant sequence identity and similar expression patterns, the tomato INO coding region was not able to complement the Arabidopsis ino mutant.

CONCLUSIONS

The similarity of effects of ino mutations on the unitegmic ovules of tobacco and the fused integuments of the Arabidopsis ats mutant show that: 1) INO orthologs play the same role in promoting integument growth in ovules of tobacco and Arabidopsis; and 2) the unitegmic ovules of tobacco (and hence other solanaceous species) are most likely the result of a congenital fusion of two ancestral integuments. Our results further indicate that INO has a conserved role in growth of the outermost cell layer of integuments. The curvature of solanaceous ovules is driven by unequal growth of the outer layers of the single integument that likely correspond to an ancestral outer integument.

The APX4 locus regulates seed vigor and seedling growth in Arabidopsis thaliana

The amino acid sequence of APX4 is similar to other ascorbate peroxidases (APXs), a group of proteins that protect plants from oxidative damage by transferring electrons from ascorbate to detoxify peroxides. In this study, we characterized two apx4 mutant alleles. Translational fusions with GFP indicated APX4 localizes to chloroplasts. Both apx4 mutant alleles formed chlorotic cotyledons with significantly reduced chlorophyll a, chlorophyll b and lutein. Given the homology of APX to ROS-scavenging proteins, this result is consistent with APX4 protecting seedling photosystems from oxidation. The growth of apx4 seedlings was stunted early in seedling development. In addition, APX4 altered seed quality by affecting seed coat formation. While apx4 seed development appeared normal, the seed coat was darker and more permeable than the wild type. In addition, accelerated aging tests showed that apx4 seeds were more sensitive to environmental stress than the wild-type seeds. If APX4 affects seed pigment biosynthesis or reduction, the seed coat color and permeability phenotypes are explained. apx4 mutants had cotyledon chlorosis, increased H₂O₂ accumulation, and reduced soluble APX activity in seedlings. These results indicate that APX4 is involved in the ROS-scavenging process in chloroplasts.

A new dual-specific incompatibility allele revealed by absence of glycosylation in the conserved C2 site of a Solanum chacoense S-RNase

The stylar determinant of gametophytic self-incompatibility (GSI) in Solanaceae, Rosaceae, and Plantaginaceae is an S-RNase encoded by a multiallelic S-locus. The primary structure of S-RNases shows five conserved (C) and two hypervariable (HV) regions, the latter forming a domain implicated in S-haplotype-specific recognition of the pollen determinant to SI. All S-RNases are glycosylated at a conserved site in the C2 region, although previous studies have shown that N-linked glycans at this position are not required for S-haplotype-specific recognition and pollen rejection. Here the incompatibility phenotype of three constructs derived from an originally monoglycosylated S11-RNase of Solanum chacoense, that were designed to explore the role of the HV domain in determining pollen recognition and the role of the N-linked glycan in the C2 region, is reported. In one series of experiments, a second glycosylation site was introduced in the HVa region to test for inhibition of pollen-specific recognition. This modification does not impede pollen rejection, although analysis shows incomplete glycosylation at the new site in the HVa region. A second construct, designed to permit complete glycosylation at the HVa site by suppression of the conserved site in the C2 region, did increase the degree of site occupancy, but, again, glycosylation was incomplete. Plants expressing this construct rejected S 11 pollen and, surprisingly, also rejected S 13 pollen, thus displaying an unusual dual specificity phenotype. This construct differs from the first by the absence of the conserved C2 glycosylation site, and thus the dual specificity is observed only in the absence of the C2 glycan. A third construct, completely lacking glycosylation sites, conferred an ability to reject only S 11 pollen, disproving the hypothesis that lack of a conserved glycan would confer a universal pollen rejection phenotype to the plant.

Transcriptome analysis of quantitative resistance-specific response upon Ralstonia solanacearum infection in tomato

Bacterial wilt, caused by the soil-borne bacterium Ralstonia solanacearum, is a lethal disease of tomato, but the molecular mechanisms of the host resistance responses to R. solanacearum remain unclear. In this study, we report the first work describing the transcriptome of cultivar resistance and susceptible tomato cultivar after inoculation with R. solanacearum. To elucidate the characteristics of resistance early in the interaction, we analyzed microarrays for resistant cultivar LS-89 and susceptible cultivar Ponderosa 1 day after stem inoculation. No change in gene expression was detected for Ponderosa, but expression levels of over 140 genes, including pathogenesis-related, hormone signaling and lignin biosynthesis genes, increased in LS-89. Expression of β-1,3-glucanase genes increased substantially. In an immunohistochemical study, glucanase in LS-89 accumulated in the xylem and pith tissues surrounding xylem vessels filled with R. solanacearum. The expression of these genes also increased in four other resistant cultivars, but changed little in four susceptible cultivars in response to R. solanacearum, suggesting that similar reactions occur in other cultivars. These gene expression profiles will serve as fundamental information to elucidate the molecular mechanisms in the resistance response to R. solanacearum in tomato.

An atypical bHLH protein encoded by POSITIVE REGULATOR OF GRAIN LENGTH 2 is involved in controlling grain length and weight of rice through interaction with a typical bHLH protein APG

Grain size is an important yield component in rice, however, genes controlling the trait remain poorly understood. Previously, we have shown that an antagonistic pair of basic helix-loop-helix (bHLH) proteins, POSITIVE REGULATOR OF GRAIN LENGTH 1 (PGL1) and ANTAGONIST OF PGL1 (APG), is involved in controlling rice grain length. Here, we report the involvement of another atypical bHLH protein gene, POSITIVE REGULATOR OF GRAIN LENGTH 2 (PGL2), in the regulation of rice grain length. Over-expression of PGL2 in the lemma/palea increased grain length and weight in correlation with the level of transgene expression. Observation of the inner epidermal cells of lemma of PGL2-overexpressing lines revealed that the long grain size is caused by an increase in cell length. PGL2 interacts with a typical bHLH protein APG, a negative regulator of rice grain length and weight, in vitro and in vivo. It was reported that overexpression of BU1 (BRASSINOSTEROID UPREGULATED 1), the closest homolog of PGL2, caused an increase in grain length. However, we detected no interaction between BU1 and APG. These findings suggest that PGL2 and PGL1 redundantly suppress the function of APG by forming heterodimers to positively regulate the rice grain length, while the pathway through which BU1, the closest homolog of PGL2, controls grain length is independent of APG.

Characterization of inflorescence-predominant chitinase gene in Metroxylon sagu via differential display

Chitinase is an enzyme that catalyzes the degradation of chitin, commonly induced upon the attack of pathogens and other stresses. A cDNA (MsChi1) was isolated from Metroxylon sagu and expressed predominantly in the inflorescence tissue of M. sagu, suggesting its role in developmental processes. The chitinase cDNA was detected and isolated via differential display and rapid amplification of cDNA ends (RACE). Primers specific to M. saguchitinase were used as probes to amplify the 3'-end and 5'-end regions of chitinase cDNA. Transcript analysis showed that chitinase is expressed in inflorescence and meristem tissues but was not detected in the leaf tissue. Sequence analysis of amplified cDNA fragments of 3'-end and 5'-end regions indicated that the chitinase cDNA was successfully amplified. The M. saguchitinase cDNA isolated was approximately 1,143 bp long and corresponds to 312 predicted amino acids. Alignments of nucleotide and amino acid have grouped this chitinase to family 19 class I chitinase.

Low responsiveness of grapevine flowers and berries at fruit set to UV-C irradiation

In grapevine, stimulation of defence responses was evidenced in response to various types of abiotic stresses in both leaves and berries, as revealed by the increasing expression of genes encoding defence-related proteins or the stimulation of their corresponding activities. However, the capability of inflorescences to respond to abiotic stresses has never been investigated. Therefore, plant defence reactions in response to UV-C irradiation were followed in inflorescences and young clusters focusing on both bunchstems (peduncle and pedicels) and developing flowers/berries from separated floral buds stage [Biologische Bundesanstalt, Bundessortenamt and CHemical industry (BBCH) stage 57] to groat-sized berries stage (BBCH 73). For this purpose, the expression of various genes coding for pathogenesis-related (PR) proteins (class I and III chitinases, Chi1b and CH3; beta-1,3-glucanase, GLUC), an enzyme of the phenylpropanoid pathway (phenylalanine ammonia-lyase, PAL), and stilbene synthase (STS) was analysed in parallel with variations of chitinase activity and the accumulation of the phytoalexin resveratrol. Multiple defence responses were induced in bunchstems of both inflorescences and clusters following UV-C treatment. First, expression of genes encoding PR proteins was stimulated and chitinase activity was enhanced. Secondly, PAL and STS expression increased in association with resveratrol accumulation. Amazingly, none of the tested defence processes was induced in grapevine flowers following UV-C exposure, whatever the stage analysed. Similarly, in berries at fruit set, induction of gene expression was weak and neither an increase in chitinase activity nor resveratrol synthesis was noticed. However, in groat-sized berries, responsiveness to UV-C increased, as revealed by the induction of CH3, PAL, and STS expression, together with resveratrol accumulation. The differential responsiveness between bunchstems, flowers, and berries is discussed.

Systemic Potato virus X infection induces defence gene expression and accumulation of β-phenylethylamine-alkaloids in potato

A better understanding of defence responses elicited during compatible plant-virus interactions is a current goal in plant pathology. We analysed defence responses during infection of Solanum tuberosum L. cv. Desiree with Potato virus X (PVX) at the transcript and metabolite level. A mostly unchanged primary metabolism reflects the compatible nature of this plant-virus interaction. Salicylic acid biosynthesis and expression of several defence genes including PR-1 and glutathione-S-transferase, which are involved in ethylene and reactive oxygen species dependent signalling, were highly up-regulated in upper-uninoculated (systemic) leaves of PVX-infected potato plants compared with mock-inoculated controls. Moreover, the β-phenylethylamine-alkaloids tyramine, octopamine, dopamine and norepinephrine were highly induced upon infection. β-phenylethylamine-alkaloids can contribute to active plant defence responses by forming hydroxycinnamic acid amides (HCAA), which are thought to increase cell wall stability by extracellular peroxidative polymerisation. Expression of tyramine-hydroxycinnamoyl transferase (THT) and apoplastic peroxidase (POD) was highly induced upon PVX infection in systemic leaves, which suggests synthesis and extracellular polymerisation of HCAA. Since cell-wall-bound ion concentrations could contribute to this process, we measured cell-wall-bound and total ion concentrations in PVX-infected and mock-inoculated leaves. The observed metabolic and transcriptional changes might represent a systemic acquired resistance response against subsequent pathogen challenge.

Molecular analysis of the conserved C4 region of the S11-RNase of Solanum chacoense

The stylar component to gametophytic self-incompatibility in Solanaceae is an S-RNase. Its primary structure has a characteristic pattern of two hypervariable regions, involved in pollen recognition, and five constant regions. Two of the latter (C2 and C3) constitute the active site, while the highly hydrophobic C1 and C5 are believed to be involved in protein stability. We analyzed the role of the C4 region by site-directed mutagenesis. A GGGG mutant, in which the four charged residues in the C4 region were replaced with glycine, did not accumulate the protein to detectable levels in styles, suggestive of a role in protein stability. A R115G mutant, in which a charged amino acid was eliminated to reduce the potential binding affinity, had no effect on the pollen rejection phenotype. This suggests the C4 does not interact with partners such as potential pollen tube receptors facilitating S-RNase uptake. Finally, a K113R mutant replaced a potential ubiquitination target with arginine. However, this RNase acted as the wild type in both incompatible and compatible crosses. The latter crosses rule out the role of the conserved C4 lysine in ubiquitination.

Molecular analysis of the stylar-expressed Solanum chacoense small asparagine-rich protein family related to the HT modifier of gametophytic self-incompatibility in Nicotiana

Gametophytic self-incompatibility (GSI) systems involving the expression of stylar ribonucleases have been described and extensively studied in many plant families including the Solanaceae, Rosaceae and Scrophulariaceae. Pollen recognition and rejection is governed in the style by specific ribonucleases called S-RNases, but in many self-incompatibility (SI) systems, modifier loci that can modulate the SI response have been described at the genetic level. Here, we present at the molecular level, the isolation and characterization of two Solanum chacoense homologues of the Nicotiana HT modifier that had been previously shown to be necessary for the SI reaction to occur in N. alata (McClure et al., 1999). HT homologues from other solanaceous species have also been isolated and a phylogenetic analysis reveals that the HT genes fall into two groups. In S. chacoense, these small proteins named ScHT-A and ScHT-B are expressed in the style and are developmentally regulated during anthesis identically to the S-RNases as well as following compatible and incompatible pollination. To elucidate the precise role of each HT isoform, antisense ScHT-A and RNAi ScHT-B lines were generated. Conversion from SI to self-compatibility (SC) was only observed in RNAi ScHT-B lines with reduced levels of ScHT-B mRNA. These results confirm the role of the HT modifier in solanaceous SI and indicate that only the HT-B isoform is directly involved in SI.

SUPERMAN attenuates positive INNER NO OUTER autoregulation to maintain polar development of Arabidopsis ovule outer integuments

The outer integument of Arabidopsis ovules exhibits marked polarity in its development, growing extensively from the abaxial side, but only to a very limited extent from the adaxial side of the ovule. Mutations in two genes affect this asymmetric growth. In strong inner no outer (ino) mutants outer integument growth is eliminated, whereas in superman (sup) mutants integument growth on the adaxial side is nearly equal to wild-type growth on the abaxial side. Through complementation and reporter gene analysis, a region of INO 5′-flanking sequences was identified that contains sufficient information for appropriate expression of INO. Using this INO promoter (P-INO) we show that INO acts as a positive regulator of transcription from P-INO, but is not sufficient for de novo initiation of transcription in other plant parts. Protein fusions demonstrate nuclear localization of INO, consistent with a proposed role as a transcription factor for this member of the YABBY protein family. Through its ability to inhibit expression of the endogenous INO gene and transgenes driven by P-INO, SUP is shown to be a negative regulator of INO transcription. Substitution of another YABBY protein coding region (CRABS CLAW) for INO overcomes this negative regulation, indicating that SUP suppresses INO transcription through attenuation of the INO positive autoregulatory loop.

Induction by pathogen, salt and drought of a basic class II chitinase mRNA and its in situ localization in pepper (Capsicum annuum)

Northern blot and in situ hybridization analyses revealed that a pepper basic class II chitinase gene (CAChi2) is constitutively expressed in floral organs and root endodermis, but not in leaf, stem and fruit of pepper. Resistance of pepper leaves to Colletotrichum coccodes infection at a late growth stage was correlated with induction of beta-1,3-glucanase and PR-1 mRNA, but not of chitinase (CAChi2) mRNA. Transcriptional activation of the CAChi2 gene in pepper leaves occurred during anthracnose development. The CAChi2 transcripts were mainly localized in phloem cells of vascular tissues of pepper leaves infected with C. coccodes. The CAChi2 gene was also differentially induced in leaf and stem tissue by treatment with abscisic acid (ABA), sodium chloride or drought. Strong accumulation of the CAChi2 transcripts occurred in pepper stem tissues due to high salt and drought, and also due to treatment with ABA. These results suggest involvement of the chitinase gene in protection of pepper plants against the pathogen, but also document cross talk with stress signals mediated by ABA, high salinity and drought.

Cultivated tomato has defects in both S-RNase and HT genes required for stylar function of self-incompatibility

Cultivated tomato (Lycopersicon esculentum), a self-compatible species, evolved from self-incompatible (SI) species in the genus Lycopersicon following a breakdown of the self-incompatibility system. In order to elucidate the molecular basis of this breakdown in L. esculentum, we first analysed the stylar proteins with an in-gel assay for ribonuclease activity and 2D-PAGE. No S-RNase protein or its activity was detected in the style of L. esculentum. We then introduced the S6-RNase gene from an SI relative, L. peruvianum, into L. esculentum. However, the styles of transgenic plants expressing S6-RNase at levels comparable to those found in the L. peruvianum style were unable to reject self-pollen and L. peruvianum pollen in an allele-specific manner. This indicated that defect in the S-RNase expression was not the sole reason for the loss of self-incompatibility in tomato. The asparagine-rich HT protein, originally identified from the style of Nicotiana alata, is the other stylar factor involved in self-incompatibility reaction. We cloned and sequenced two distinct genes encoding HT-A and HT-B proteins from L. peruvianum (LpHT-A and LpHT-B) and L. esculentum (LeHT-A and LeHT-B). A frame shift mutation in the coding sequence of LeHT-A and a stop codon in the ORF of LeHT-B were found, and no LeHT-B transcript was detected in the style of L. esculentum. The results suggest that the breakdown of self-incompatibility in cultivated tomato is associated with loss-of-function mutations in both S-RNase and HT genes.

Differential expression patterns of an acidic chitinase and a basic chitinase in the root nodule of Elaeagnus umbellata

Two cDNA clones encoding chitinase were isolated from a root nodule cDNA library of Elaeagnus umbellata by the hybridization-competition method. The two clones, EuNOD-CHT1 and EuNOD-CHT2, encode for 335 and 317 amino acid residues with the molecular mass of mature proteins being 33.3 and 31.1 kDa, respectively. The two chitinases showed similar protein structures consisting of four domains: hydrophobic signal peptide domain, cysteine-rich chitin-binding domain, hinge domain, and catalytic domain. The EuNOD-CHT1 gene showed similar expression levels in root nodules and leaves, with no detection of transcripts in the roots. The EuNOD-CHT2 gene was expressed at similarly high levels in the roots and root nodules, but at a very low level in the leaves. In situ hybridization showed that EuNOD-CHT1 transcripts were strongly detected in the meristem zone, but weakly detected in the outer cortex layer of the root nodule and in the uninfected cells of the fixation zone. On the other hand, EuNOD-CHT2 transcripts were strongly detected in the infected cells of the fixation zone and central vascular system, but weakly detected in the senescence zone. Our results suggest that the two chitinases may play different biological roles in the root nodule. EuNOD-CHT2 may be involved in a defense response against internal symbionts, external pathogens, or both, while EuNOD-CHT1 may be involved in normal plant development as well as in a defensive role against external pathogens.

Class I beta-1,3-glucanase and chitinase are expressed in the micropylar endosperm of tomato seeds prior to radicle emergence

beta-1,3-Glucanase (EC 3.2.1.39) and chitinase (EC 3.2.1.14) mRNAs, proteins, and enzyme activities were expressed specifically in the micropylar tissues of imbibed tomato (Lycopersicon esculentum Mill.) seeds prior to radicle emergence. RNA hybridization and immunoblotting demonstrated that both enzymes were class I basic isoforms. beta-1,3-Glucanase was expressed exclusively in the endosperm cap tissue, whereas chitinase localized to both endosperm cap and radicle tip tissues. beta-1,3-Glucanase and chitinase appeared in the micropylar tissues of gibberellin-deficient gib-1 tomato seeds only when supplied with gibberellin. Accumulation of beta-1,3-glucanase mRNA, protein and enzyme activity was reduced by 100 microM abscisic acid, which delayed or prevented radicle emergence but not endosperm cap weakening. In contrast, expression of chitinase mRNA, protein, and enzyme activity was not affected by abscisic acid. Neither of these enzymes significantly hydrolyzed isolated tomato endosperm cap cell walls. Although both beta-1,3-glucanase and chitinase were expressed in tomato endosperm cap tissue prior to radicle emergence, we found no evidence that they were directly involved in cell wall modification or tissue weakening. Possible functions of these hydrolases during tomato seed germination are discussed.

Two differentially regulated class II chitinases from parsley

Two distinct cDNA clones, PcCHI1 and PcCHI2, with high sequence similarity to plant chitinases were isolated from parsley (Petroselinum crispum), expressed in Escherichia coli, and the encoded proteins functionally identified as endochitinases. Different expression patterns of the corresponding mRNAs and proteins in infected and uninfected parsley plants indicated distinct roles of the two isoforms in both pathogen defense and plant development. Infection of parsley leaf buds with Phytophthora sojae resulted in the rapid, transient and highly localized accumulation of PcCHI1 mRNA and protein around infection sites, whereas PcCHI2 mRNA and protein were systemically induced at later infection stages. Similar differences in the timing of induction were observed in elicitor-treated, suspension-cultured parsley cells. In uninfected plants, PcCHI1 mRNA was particularly abundant in the transmitting tract of healthy flowers, suggesting a role in the constitutive protection of susceptible transmitting tissue of the style against pathogen ingress and/or in the fertilization process, possibly by affecting pollen tube growth. Localization of PcCHI2 mRNA and protein in the parenchymatic collenchyme of young pedicels may indicate a function in the constitutive protection of this tissue. In addition to such distinct roles of PcCHI1 and PcCHI2 in preformed and induced pathogen defense, both chitinases may have endogenous regulatory functions in plant development.

Analysis of gene promoters for two tomato polygalacturonases expressed in abscission zones and the stigma

The tomato (Lycopersicon esculentum cv Ailsa Craig) polygalacturonase genes TAPG1 (LYCes;Pga1;2) and TAPG4 (LYCes;Pga1;5) are abundantly expressed in both abscission zones and the pistils of mature flowers. To further investigate the spatial and temporal expression patterns for these genes, the TAPG gene promoters were ligated to beta-glucuronidase (GUS) reporter genes and transformed into tomato. GUS expression with both constructs was similar and entirely consistent with the expression patterns of the native gene transcripts. GUS activity was observed in the weakening abscission zones of the leaf petiole, flower and fruit pedicel, flower corolla, and fruit calyx. In leaf petiole and flower pedicel zones this activity was enhanced by ethylene and inhibited by indole-3-acetic acid. On induction of abscission with ethylene, GUS accumulation was much earlier in TAPG4:GUS than in TAPG1:GUS transformants. Moreover, TAPG4:GUS staining appeared to predominate in the vascular bundles relative to surrounding cortex cells whereas TAPG1:GUS was more evenly distributed across the separation layer. Like the native genes, GUS was also expressed in the stigma. Activity was not apparent in pistils until the flowers had opened and was confined to the stigma and style immediately proximal to it. A minimal promoter construct consisting of a 247-bp 5'-upstream element from TAPG1 was found to be sufficient to direct GUS expression in both abscission zones and the stigma.