BECLIN1 from Arabidopsis thaliana under the generic control of regulated expression systems, a strategy for developing male sterile plants

Arabidopsis BECLIN1-induced autophagy mediates reprogramming in tapetal programmed cell death by altering the gross cellular homeostasis

In flowering plants, the tapetum degeneration in post-meiotic anther occurs through developmental programmed cell death (dPCD), which is one of the most critical and sensitive steps for the proper development of male gametophytes and fertility. Yet the pathways of dPCD, its regulation, and its interaction with autophagy remain elusive. Here, we report that high-level expression of Arabidopsis autophagy-related gene BECLIN1 (BECN1 or AtATG6) in the tobacco tapetum prior to their dPCD resulted in developmental defects. BECN1 induces severe autophagy and multiple cytoplasm-to-vacuole pathways, which alters tapetal cell reactive oxygen species (ROS)-homeostasis that represses the tapetal dPCD. The transcriptome analysis reveals that BECN1- expression caused major changes in the pathway, resulting in altered cellular homeostasis in the tapetal cell. Moreover, BECN1-mediated autophagy reprograms the execution of tapetal PCD by altering the expression of the key developmental PCD marker genes: SCPL48, CEP1, DMP4, BFN1, MC9, EXI1, and Bcl-2 member BAG5, and BAG6. This study demonstrates that BECN1-mediated autophagy is inhibitory to the dPCD of the tapetum, but the severity of autophagy leads to autophagic death in the later stages. The delayed and altered mode of tapetal degeneration resulted in male sterility.

Male sterility in plants: an overview of advancements from natural CMS to genetically manipulated systems for hybrid seed production

KEY MESSAGE

The male sterility system in plants has traditionally been utilized for hybrid seed production. In last three decades, genetic manipulation for male sterility has revolutionized this area of research related to hybrid seed production technology. Here, we have surveyed some of the natural cytoplasmic male sterility (CMS) systems that existed/ were developed in different crop plants for developing male sterility-fertility restoration systems used in hybrid seed production and highlighted some of the recent biotechnological advancements in the development of genetically engineered systems that occurred in this area. We have indicated the possible future directions toward the development of engineered male sterility systems. Cytoplasmic male sterility (CMS) is an important trait that is naturally prevalent in many plant species, which has been used in the development of hybrid varieties. This is associated with the use of appropriate genes for fertility restoration provided by the restorer line that restores fertility on the corresponding CMS line. The development of hybrids based on a CMS system has been demonstrated in several different crops. However, there are examples of species, which do not have usable cytoplasmic male sterility and fertility restoration systems (Cytoplasmic Genetic Male Sterility Systems-CGMS) for hybrid variety development. In such plants, it is necessary to develop usable male sterile lines through genetic engineering with the use of heterologous expression of suitable genes that control the development of male gametophyte and fertile male gamete formation. They can also be developed through gene editing using the recently developed CRISPR-Cas technology to knock out suitable genes that are responsible for the development of male gametes. The present review aims at providing an insight into the development of various technologies for successful production of hybrid varieties and is intended to provide only essential information on male sterility systems starting from naturally occurring ones to the genetically engineered systems obtained through different means.

SlMYB72 affects pollen development by regulating autophagy in tomato

The formation and development of pollen are among the most critical processes for reproduction and genetic diversity in the life cycle of flowering plants. The present study found that SlMYB72 was highly expressed in the pollen and tapetum of tomato flowers. Downregulation of SlMYB72 led to a decrease in the amounts of seeds due to abnormal pollen development compared with wild-type plants. Downregulation of SlMYB72 delayed tapetum degradation and inhibited autophagy in tomato anther. Overexpression of SlMYB72 led to abnormal pollen development and delayed tapetum degradation. Expression levels of some autophagy-related genes (ATGs) were decreased in SlMYB72 downregulated plants and increased in overexpression plants. SlMYB72 was directly bound to ACCAAC/ACCAAA motif of the SlATG7 promoter and activated its expression. Downregulation of SlATG7 inhibited the autophagy process and tapetum degradation, resulting in abnormal pollen development in tomatoes. These results indicated SlMYB72 affects the tapetum degradation and pollen development by transcriptional activation of SlATG7 and autophagy in tomato anther. The study expands the understanding of the regulation of autophagy by SlMYB72, uncovers the critical role that autophagy plays in pollen development, and provides potential candidate genes for the production of male-sterility in plants.

Identification and validation of the wound and insect bite early inducible promoter from Arabidopsis thaliana

A wound-inducible promoter facilitates the regulated gene expression at the targeted site during the time of mechanical stress or infestation by the pathogen. The present work has aimed to identify a wound-inducible promoter that expresses at early time points preceding wound-stress treatment in Arabidopsis thaliana. The computational analysis of microarray data (GSE5627) resulted in the identification of five early inducible genes, viz., AT1G17380, AT1G80440, AT2G43530, AT3G48360, and AT5G13220. The RT-PCR analysis showed AT5G13220 (JASMONATE-ASSOCIATED 1) gene induced at a significantly higher level post 30 min of wounding. Thus, the promoter of the highly induced and early expressed wound-inducible gene, AT5G13220 (named PW220), was characterized by fusing with β-glucuronidase (gusA) reporter or Cry1EC genes. The fluorometric analysis and histochemical staining of the gusA gene and quantitative estimation of Cry1EC protein in Nicotiana tabacum transgenic lines confirmed wound-induced expression characteristic of the selected promoter. Insect bioassay suggested that wound-inducible and constitutive expression of Cry1EC protein in transgenic lines showed a similar level of protection against different instar Spodoptera litura larvae. Furthermore, we identified that abscisic acid influenced the wound-specific expression of the selected PW220 promoter in the transgenic lines, which correlates with the presence of conserved cis-regulatory elements associated with dehydration and abscisic acid responses. Altogether, our results suggested that the wound-inducible promoter PW220 provides an excellent alternative for developing insect-tolerant transgenic crops in the future.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-022-03143-0.

Potential Association of Reactive Oxygen Species With Male Sterility in Peach

Male sterility is an important agronomic trait for hybrid vigor utilization and hybrid seed production, but its underlying mechanisms remain to be uncovered. Here, we investigated the mechanisms of male sterility in peach using a combined cytology, physiology, and molecular approach. Cytological features of male sterility include deformed microspores and tapetum cells along with absence of pollen grains. Microspores had smaller nucleus at the mononuclear stage and were compressed into belts and subsequently disappeared in the anther cavity, whereas tapetum cells were swollen and vacuolated, with a delayed degradation to flowering time. Male sterile anthers had an ROS burst and lower levels of major antioxidants, which may cause abnormal development of microspores and tapetum, leading to male sterility in peach. In addition, the male sterility appears to be cytoplasmic in peach, which could be due to sequence variation in the mitochondrial genome. Our results are helpful for further investigation of the genetic mechanisms underlying male sterility in peach.

A proteomic study of cysteine protease induced cell death in anthers of male sterile tobacco transgenic plants

Manifestation of male sterility in plants is an important requirement for hybrid seed production. Tapetum cell layer of anther is a primary target for genetic manipulation for male sterility. In our previous report, the targeted expression of Arachis cysteine protease in tapetum led to premature degeneration of tapetal layer that resulted in complete male sterility in transgenic tobacco plants. To correlate cysteine protease mediated cell death of tapetum, transmission electron microscopy (TEM) and proteomic pattern of anthers of cysteine protease induced male sterile plant were compared with the untransformed control plant. TEM study revealed the abnormal growth of tapetal cells exhibiting excessive vacuolization that synchronized with irregular exine wall formation of the microspores. In anther proteome, a total 250 protein spots were detected that were reproducible and exhibited similar distribution pattern. Further, anther proteome of male sterile plant showed the significant upregulation (≥ 1.5) of 56 protein spots. Using Mass spectroscopy (MALDI TOF/TOF), we have identified 14 protein spots that were involved in several processes such as energy metabolism, protein synthesis, plastid protein, lipid metabolism, and cell wall assembly. Upregulation of patatin-like protein-2 homolog, carboxylesterase 17 and dicer like protein-4 in male sterile anthers that have been demonstrated to induce cell death, suggesting that cysteine protease mediated premature tapetal cell death might involve the lipid peroxidation pathway in coordination with gene silencing mechanism.

Construction of a multicontrol sterility system for a maize male-sterile line and hybrid seed production based on the ZmMs7 gene encoding a PHD-finger transcription factor

Although hundreds of genetic male sterility (GMS) mutants have been identified in maize, few are commercially used due to a lack of effective methods to produce large quantities of pure male-sterile seeds. Here, we develop a multicontrol sterility (MCS) system based on the maize male sterility 7 (ms7) mutant and its wild-type Zea mays Male sterility 7 (ZmMs7) gene via a transgenic strategy, leading to the utilization of GMS in hybrid seed production. ZmMs7 is isolated by a map-based cloning approach and encodes a PHD-finger transcription factor orthologous to rice PTC1 and Arabidopsis MS1. The MCS transgenic maintainer lines are developed based on the ms7-6007 mutant transformed with MCS constructs containing the (i) ZmMs7 gene to restore fertility, (ii) α-amylase gene ZmAA and/or (iii) DNA adenine methylase gene Dam to devitalize transgenic pollen, (iv) red fluorescence protein gene DsRed2 or mCherry to mark transgenic seeds and (v) herbicide-resistant gene Bar for transgenic seed selection. Self-pollination of the MCS transgenic maintainer line produces transgenic red fluorescent seeds and nontransgenic normal colour seeds at a 1:1 ratio. Among them, all the fluorescent seeds are male fertile, but the seeds with a normal colour are male sterile. Cross-pollination of the transgenic plants to male-sterile plants propagates male-sterile seeds with high purity. Moreover, the transgene transmission rate through pollen of transgenic plants harbouring two pollen-disrupted genes is lower than that containing one pollen-disrupted gene. The MCS system has great potential to enhance the efficiency of maize male-sterile line propagation and commercial hybrid seed production.

New Insights Into Beclin-1: Evolution and Pan-Malignancy Inhibitor Activity

Autophagy is a functionally conserved self-degradation process that facilitates the survival of eukaryotic life via the management of cellular bioenergetics and maintenance of the fidelity of genomic DNA. The first known autophagy inducer was Beclin-1. Beclin-1 is expressed in multicellular eukaryotes ranging throughout plants to animals, comprising a nonmonophyllic group, as shown in this report via aggressive BLAST searches. In humans, Beclin-1 is a haploinsuffient tumor suppressor as biallelic deletions have not been observed in patient tumors clinically. Therefore, Beclin-1 fails the Knudson hypothesis, implicating expression of at least one Beclin-1 allele is essential for cancer cell survival. However, Beclin-1 is frequently monoallelically deleted in advanced human cancers and the expression of two Beclin-1 allelles is associated with greater anticancer effects. Overall, experimental evidence suggests that Beclin-1 inhibits tumor formation, angiogenesis, and metastasis alone and in cooperation with the tumor suppressive molecules UVRAG, Bif-1, Ambra1, and MDA-7/IL-24 via diverse mechanisms of action. Conversely, Beclin-1 is upregulated in cancer stem cells (CSCs), portending a role in cancer recurrence, and highlighting this molecule as an intriguing molecular target for the treatment of CSCs. Many aspects of Beclin-1's biological effects remain to be studied. The consequences of these BLAST searches on the molecular evolution of Beclin-1, and the eukaryotic branches of the tree of life, are discussed here in greater detail with future inquiry focused upon protist taxa. Also in this review, the effects of Beclin-1 on tumor suppression and cancer malignancy are discussed. Beclin-1 holds significant promise for the development of novel targeted cancer therapeutics and is anticipated to lead to a many advances in our understanding of eukaryotic evolution, multicellularity, and even the treatment of CSCs in the coming decades.

Molecular Approaches for Manipulating Male Sterility and Strategies for Fertility Restoration in Plants

Usable pollination control systems have proven to be effective system for the development of hybrid crop varieties, which are important for optimal performance over varied environments and years. They also act as a biocontainment to check horizontal transgene flow. In the last two decades, many genetic manipulations involving genes controlling the production of cytotoxic products, conditional male sterility, altering metabolic processes, post-transcriptional gene silencing, RNA editing and chloroplast engineering methods have been used to develop a proper pollination control system. In this review article, we outline the approaches used for generating male sterile plants using an effective pollination control system to highlight the recent progress that occurred in this area. Furthermore, we propose possible future directions for biotechnological improvements that will allow the farmers to buy hybrid seed once for many generations in a cost-effective manner.

Development of an inducible male-sterility system in rice through pollen-specific expression of l-ornithinase (argE) gene of E. coli

In the present investigation, an inducible male-sterility system has been developed in the rice. In order to introduce inducible male-sterility, the coding region of l-ornithinase (argE) gene of E. coli was fused to the Oryza sativa indica pollen allergen (OSIPA) promoter sequence which is known to function specifically in the pollen grains. Transgenic plants were obtained with argE gene and the transgenic status of plants was confirmed by PCR and Southern blot analyses. RT-PCR analysis confirmed the tissue-specific expression of argE in the anthers of transgenic rice plants. Transgenic rice plants expressing argE, after application of N-acetyl-phosphinothricin (N-ac-PPT), became completely male-sterile owing to the pollen-specific expression of argE. However, argE-transgenic plants were found to be self fertile when N-ac-PPT was not applied. Normal fertile seeds were obtained from the cross pollination between male-sterile argE transgenics and untransformed control plants, indicating that the female fertility is not affected by the N-ac-PPT treatment. These results clearly suggest that the expression of argE gene affects only the male gametophyte but not the gynoecium development. Induction of complete male-sterility in the rice is a first of its kind, and moreover this male- sterility system does not require the deployment of any specific restorer line.

Application of rice microspore-preferred promoters to manipulate early pollen development in Arabidopsis: a heterologous system

Rice microspore-promoters. Based on microarray data analyzed for developing anthers and pollen grains, we identified nine rice microspore-preferred (RMP) genes, designated RMP1 through RMP9. To extend their biotechnological applicability, we then investigated the activity of RMP promoters originating from monocotyledonous rice in a heterologous system of dicotyledonous Arabidopsis. Expression of GUS was significantly induced in transgenic plants from the microspore to the mature pollen stages and was driven by the RMP1, RMP3, RMP4, RMP5, and RMP9 promoters. We found it interesting that, whereas RMP2 and RMP6 directed GUS expression in microspore at the early unicellular and bicellular stages, RMP7 and RMP8 seemed to be expressed at the late tricellular and mature pollen stages. Moreover, GUS was expressed in seven promoters, RMP3 through RMP9, during the seedling stage, in immature leaves, cotyledons, and roots. To confirm microspore-specific expression, we used complementation analysis with an Arabidopsis male-specific gametophytic mutant, sidecar pollen-2 (scp-2), to verify the activity of three promoters. That mutant shows defects in microspore development prior to pollen mitosis I. These results provide strong evidence that the SIDECAR POLLEN gene, driven by RMP promoters, successfully complements the scp-2 mutation, and they strongly suggest that these promoters can potentially be applied for manipulating the expression of target genes at the microspore stage in various species.

Targeted expression of cystatin restores fertility in cysteine protease induced male sterile tobacco plants

Fertility restoration in male sterile plants is an essential requirement for their utilization in hybrid seed production. In an earlier investigation, we have demonstrated that the targeted expression of a cysteine protease in tapetal cell layer resulted in complete male sterility in tobacco transgenic plants. In the present investigation, we have used a cystatin gene, which encodes for a cysteine protease inhibitor, from a wild peanut, Arachis diogoi and developed a plant gene based restoration system for cysteine protease induced male sterile transgenic tobacco plants. We confirmed the interaction between the cysteine protease and a cystatin of the wild peanut, A. diogoi through in silico modeling and yeast two-hybrid assay. Pollen from primary transgenic tobacco plants expressing cystatin gene under the tapetum specific promoter- TA29 restored fertility on cysteine protease induced male sterile tobacco plants developed earlier. This has confirmed the in vivo interaction of cysteine protease and cystatin in the tapetal cells, and the inactivation of cysteine protease and modulation of its negative effects on pollen fertility. Both the cysteine protease and cystatin genes are of plant origin in contrast to the analogous barnase-barstar system that deploys genes of prokaryotic origin. Because of the deployment of genes of plant origin, this system might not face biosafety problems in developing hybrids in food crops.

Spt-Ada-Gcn5-Acetyltransferase (SAGA) Complex in Plants: Genome Wide Identification, Evolutionary Conservation and Functional Determination

The recruitment of RNA polymerase II on a promoter is assisted by the assembly of basal transcriptional machinery in eukaryotes. The Spt-Ada-Gcn5-Acetyltransferase (SAGA) complex plays an important role in transcription regulation in eukaryotes. However, even in the advent of genome sequencing of various plants, SAGA complex has been poorly defined for their components and roles in plant development and physiological functions. Computational analysis of Arabidopsis thaliana and Oryza sativa genomes for SAGA complex resulted in the identification of 17 to 18 potential candidates for SAGA subunits. We have further classified the SAGA complex based on the conserved domains. Phylogenetic analysis revealed that the SAGA complex proteins are evolutionary conserved between plants, yeast and mammals. Functional annotation showed that they participate not only in chromatin remodeling and gene regulation, but also in different biological processes, which could be indirect and possibly mediated via the regulation of gene expression. The in silico expression analysis of the SAGA components in Arabidopsis and O. sativa clearly indicates that its components have a distinct expression profile at different developmental stages. The co-expression analysis of the SAGA components suggests that many of these subunits co-express at different developmental stages, during hormonal interaction and in response to stress conditions. Quantitative real-time PCR analysis of SAGA component genes further confirmed their expression in different plant tissues and stresses. The expression of representative salt, heat and light inducible genes were affected in mutant lines of SAGA subunits in Arabidopsis. Altogether, the present study reveals expedient evidences of involvement of the SAGA complex in plant gene regulation and stress responses.

A novel male sterility-fertility restoration system in plants for hybrid seed production

Hybrid seeds are used for stimulated crop production, as they harness heterosis. The achievement of complete male-sterility in the female-parent and the restored-fertility in F1-hybrids are the major bottlenecks in the commercial hybrid seed production. Here, we report a male sterility-fertility restoration system by engineering the in most nutritive anther wall layer tapetum of female and male parents. In the female parent, high-level, and stringent expression of Arabidopsis autophagy-related gene BECLIN1 was achieved in the tapetum, which altered the tapetal degeneration program, leading to male sterility. This works on our previously demonstrated expression cassette based on functional complementation of TATA-box mutant (TGTA) promoter and TATA-binding protein mutant3 (TBPm3), with modification by conjugating Long Hypocotyle in Far-Red1 fragment (HFR1(NT131)) with TBPm3 (HFR1(NT131)-TBPm3) to exercise regulatory control over it. In the male parent, tapetum-specific Constitutive photo-morphogenesis1 (COP1) was expressed. The F1 obtained by crossing these engineered parents showed decreased BECLIN1 expression, which was further completely abolished when COP1-mutant (COP1(L105A)) was used as a male parent, leading to normal tapetal development and restored fertility. The system works on COP1-HFR1 interaction and COP1-mediated degradation of TBPm3 pool (HFR1(NT131)-TBPm3). The system can be deployed for hybrid seed production in agricultural crops.

Grafting triggers differential responses between scion and rootstock

Grafting is a well-established practice to facilitate asexual propagation in horticultural and agricultural crops. It has become a method for studying molecular aspects of root-to-shoot and/or shoot-to-root signaling events. The objective of this study was to investigate differences in gene expression between the organs of the scion and rootstock of a homograft (Arabidopsis thaliana). MapMan and Gene Ontology enrichment analysis revealed differentially expressed genes from numerous functional categories related to stress responses in the developing flower buds and leaves of scion and rootstock. Meta-analysis suggested induction of drought-type responses in flower buds and leaves of the scion. The flower buds of scion showed over-representation of the transcription factor genes, such as Homeobox, NAC, MYB, bHLH, B3, C3HC4, PLATZ etc. The scion leaves exhibited higher accumulation of the regulatory genes for flower development, such as SEPALLATA 1-4, Jumonji C and AHL16. Differential transcription of genes related to ethylene, gibberellic acid and other stimuli was observed between scion and rootstock. The study is useful in understanding the molecular basis of grafting and acclimation of scion on rootstock.

Comparative transcriptional profiling of two wheat genotypes, with contrasting levels of minerals in grains, shows expression differences during grain filling

Wheat is one of the most important cereal crops in the world. To identify the candidate genes for mineral accumulation, it is important to examine differential transcriptome between wheat genotypes, with contrasting levels of minerals in grains. A transcriptional comparison of developing grains was carried out between two wheat genotypes- Triticum aestivum Cv. WL711 (low grain mineral), and T. aestivum L. IITR26 (high grain mineral), using Affymetrix GeneChip Wheat Genome Array. The study identified a total of 580 probe sets as differentially expressed (with log2 fold change of ≥2 at p≤0.01) between the two genotypes, during grain filling. Transcripts with significant differences in induction or repression between the two genotypes included genes related to metal homeostasis, metal tolerance, lignin and flavonoid biosynthesis, amino acid and protein transport, vacuolar-sorting receptor, aquaporins, and stress responses. Meta-analysis revealed spatial and temporal signatures of a majority of the differentially regulated transcripts.

Expression of a pathogen-induced cysteine protease (AdCP) in tapetum results in male sterility in transgenic tobacco

Usable male sterility systems have immense potential in developing hybrid varieties in crop plants, which can also be used as a biological safety containment to prevent horizontal transgene flow. Barnase-Barstar system developed earlier was the first approach to engineer male sterility in plants. In an analogous situation, we have evolved a system of inducing pollen abortion and male sterility in transgenic tobacco by expressing a plant gene coding for a protein with known developmental function in contrast to the Barnase-Barstar system, which deploys genes of prokaryotic origin, i.e., from Bacillus amyloliquefaciens. We have used a plant pathogen-induced gene, cysteine protease for inducing male sterility. This gene was identified in the wild peanut, Arachis diogoi differentially expressed when it was challenged with the late leaf spot pathogen, Phaeoisariopsis personata. Arachis diogoi cysteine protease (AdCP) was expressed under the strong tapetum-specific promoter (TA29) and tobacco transformants were generated. Morphological and histological analysis of AdCP transgenic plants showed ablated tapetum and complete pollen abortion in three transgenic lines. Furthermore, transcript analysis displayed the expression of cysteine protease in these male sterile lines and the expression of the protein was identified in western blot analysis using its polyclonal antibody raised in the rabbit system.

Enhanced methanol production in plants provides broad spectrum insect resistance

Plants naturally emit methanol as volatile organic compound. Methanol is toxic to insect pests; but the quantity produced by most of the plants is not enough to protect them against invading insect pests. In the present study, we demonstrated that the over-expression of pectin methylesterase, derived from Arabidopsis thaliana and Aspergillus niger, in transgenic tobacco plants enhances methanol production and resistance to polyphagous insect pests. Methanol content in the leaves of transgenic plants was measured using proton nuclear spectroscopy (1H NMR) and spectra showed up to 16 fold higher methanol as compared to control wild type (WT) plants. A maximum of 100 and 85% mortality in chewing insects Helicoverpa armigera and Spodoptera litura larvae was observed, respectively when fed on transgenic plants leaves. The surviving larvae showed less feeding, severe growth retardation and could not develop into pupae. In-planta bioassay on transgenic lines showed up to 99 and 75% reduction in the population multiplication of plant sap sucking pests Myzus persicae (aphid) and Bemisia tabaci (whitefly), respectively. Most of the phenotypic characters of transgenic plants were similar to WT plants. Confocal microscopy showed no deformities in cellular integrity, structure and density of stomata and trichomes of transgenic plants compared to WT. Pollen germination and tube formation was also not affected in transgenic plants. Cell wall enzyme transcript levels were comparable with WT. This study demonstrated for the first time that methanol emission can be utilized for imparting broad range insect resistance in plants.

RNAi silencing of three homologues of S-adenosylmethionine decarboxylase gene in tapetal tissue of tomato results in male sterility

Polyamines play very important role in various cellular metabolic functions, including floral induction, floral differentiation and fertility regulation. In the present study, S-adenosylmethionine decarboxylase (SAMDC), a key gene involved in polyamine biosynthesis, has been targeted in tapetal tissue of tomato using RNAi to examine its effect on tapetum development and pollen viability. The target SAMDC gene fragments of three homologues were cloned in a hairpin RNA construct under the control of tapetal-specific A9 promoter, which was used to generate several RNAi tomato plants. These RNAi lines expressed the intended small interfering RNAs in the anther and showed the aborted and sterile pollen exhibiting shrunken and distorted morphology. These RNAi tomato plants having sterile pollen, failed to set fruits but female fertility of the plants remained unaffected as cross pollination resulted in fruit setting. Expression profiling of SAMDC genes showed considerable decrease in transcripts of SAMDC1 (5-8 fold) and SAMDC2 and SAMDC3 (2-3 fold) in the anthers of RNAi plants. The other polyamine biosynthesis genes, ADC and SPDSYN exhibited ~1.5 fold decrease in their transcript levels. Presence of siRNA molecules specific to SAMDC homologues in anther and tapetal-specific activity of A9 promoter as shown with GUS reporter system of RNAi plants suggested down-regulation of the target genes in tapetum by RNAi. These observations indicate the importance of SAMDC, in turn polyamines in pollen development, and thus tapetum-specific down-regulation of SAMDC genes using RNAi can be used for developing male sterile plants.