Reduced expression of BjRCE1 gene modulated by nuclear-cytoplasmic incompatibility alters auxin response in cytoplasmic male-sterile Brassica juncea

Down-regulation of the Sucrose Transporter CsSUT1 Causes Male Sterility by Altering Carbohydrate Supply

In plants, male sterility is an important agronomic trait, especially in hybrid crop production. Many factors are known to affect crop male sterility, but it remains unclear whether Suc transporters (SUTs) participate directly in this process. Here, we identified and functionally characterized the cucumber (Cucumis sativus) CsSUT1, a typical plasma membrane-localized energy-dependent high-affinity Suc-H⁺ symporter. CsSUT1 is expressed in male flowers and encodes a protein that is localized primarily in the tapetum, pollen, and companion cells of the phloem of sepals, petals, filaments, and pedicel. The male flowers of CsSUT1-RNA interference (RNAi) lines exhibited a decrease in Suc, hexose, and starch content, relative to those of the wild type, during the later stages of male flower development, a finding that was highly associated with male sterility. Transcriptomic analysis revealed that numerous genes associated with sugar metabolism, transport, and signaling, as well as with auxin signaling, were down-regulated, whereas most myeloblastosis (MYB) transcription factor genes were up-regulated in these CsSUT1-RNAi lines relative to wild type. Our findings demonstrate that male sterility can be induced by RNAi-mediated down-regulation of CsSUT1 expression, through the resultant perturbation in carbohydrate delivery and subsequent alteration in sugar and hormone signaling and up-regulation of specific MYB transcription factors. This knowledge provides a new approach for bioengineering male sterility in crop plants.

Comparative transcriptomic analyses of normal and malformed flowers in sugar apple (Annona squamosa L.) to identify the differential expressed genes between normal and malformed flowers

BACKGROUND

Sugar apple (Annona squamosa L.), a popular fruit with high medicinal and nutritional properties, is widely cultivated in tropical South Asia and America. The malformed flower is a major cause for a reduction in production of sugar apple. However, little information is available on the differences between normal and malformed flowers of sugar apple.

RESULTS

To gain a comprehensive perspective on the differences between normal and malformed flowers of sugar apple, cDNA libraries from normal and malformation flowers were prepared independently for Illumina sequencing. The data generated a total of 70,189,896 reads that were integrated and assembled into 55,097 unigenes with a mean length of 783 bp. A large number of differentially expressed genes (DEGs) were identified. Among these DEGs, 701 flower development-associated transcript factor encoding genes were included. Furthermore, a large number of flowering- and hormone-related DEGs were also identified, and most of these genes were down-regulated expressed in the malformation flowers. The expression levels of 15 selected genes were validated using quantitative-PCR. The contents of several endogenous hormones were measured. The malformed flowers displayed lower endogenous hormone levels compared to the normal flowers.

CONCLUSIONS

The expression data as well as hormone levels in our study will serve as a comprehensive resource for investigating the regulation mechanism involved in floral organ development in sugar apple.

Identification and Expression Profiling of the Auxin Response Factors in Dendrobium officinale under Abiotic Stresses

Auxin response factor (ARF) proteins play roles in plant responses to diverse environmental stresses by binding specifically to the auxin response element in the promoters of target genes. Using our latest public Dendrobium transcriptomes, a comprehensive characterization and analysis of 14 DnARF genes were performed. Three selected DnARFs, including DnARF1, DnARF4, and DnARF6, were confirmed to be nuclear proteins according to their transient expression in epidermal cells of Nicotiana benthamiana leaves. Furthermore, the transcription activation abilities of DnARF1, DnARF4, and DnARF6 were tested in a yeast system. Our data showed that DnARF6 is a transcriptional activator in Dendrobium officinale. To uncover the basic information of DnARF gene responses to abiotic stresses, we analyzed their expression patterns under various hormones and abiotic treatments. Based on our data, several hormones and significant stress responsive DnARF genes have been identified. Since auxin and ARF genes have been identified in many plant species, our data is imperative to reveal the function of ARF mediated auxin signaling in the adaptation to the challenging Dendrobium environment.

High-throughput sequencing and degradome analysis reveal altered expression of miRNAs and their targets in a male-sterile cybrid pummelo (Citrus grandis)

Background

G1 + HBP is a male sterile cybrid line with nuclear genome from Hirado Buntan pummelo (C. grandis Osbeck) (HBP) and mitochondrial genome from “Guoqing No.1” (G1, Satsuma mandarin), which provides a good opportunity to study male sterility and nuclear-cytoplasmic cross talk in citrus. High-throughput sRNA and degradome sequencing were applied to identify miRNAs and their targets in G1 + HBP and its fertile type HBP during reproductive development.

Results

A total of 184 known miRNAs, 22 novel miRNAs and 86 target genes were identified. Some of the targets are transcription factors involved in floral development, such as auxin response factors (ARFs), SQUAMOSA promoter binding protein box (SBP-box), MYB, basic region-leucine zipper (bZIP), APETALA2 (AP2) and transport inhibitor response 1 (TIR1). Eight target genes were confirmed to be sliced by corresponding miRNAs using 5’ RACE technology. Based on the sequencing abundance, 42 differentially expressed miRNAs between sterile line G1 + HBP and fertile line HBP were identified. Differential expression of miRNAs and their target genes between two lines was validated by quantitative RT-PCR, and reciprocal expression patterns between some miRNAs and their targets were demonstrated. The regulatory mechanism of miR167a was investigated by yeast one-hybrid and dual-luciferase assays that one dehydrate responsive element binding (DREB) transcription factor binds to miR167a promoter and transcriptionally repress miR167 expression.

Conclusion

Our study reveals the altered expression of miRNAs and their target genes in a male sterile line of pummelo and highlights that miRNA regulatory network may be involved in floral bud development and cytoplasmic male sterility in citrus.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2882-0) contains supplementary material, which is available to authorized users.

Cytoplasmic male sterility in Brassicaceae crops

Brassicaceae crops display strong hybrid vigor, and have long been subject to F1 hybrid breeding. Because the most reliable system of F1 seed production is based on cytoplasmic male sterility (CMS), various types of CMS have been developed and adopted in practice to breed Brassicaceae oil seed and vegetable crops. CMS is a maternally inherited trait encoded in the mitochondrial genome, and the male sterile phenotype arises as a result of interaction of a mitochondrial CMS gene and a nuclear fertility restoring (Rf) gene. Therefore, CMS has been intensively investigated for gaining basic insights into molecular aspects of nuclear-mitochondrial genome interactions and for practical applications in plant breeding. Several CMS genes have been identified by molecular genetic studies, including Ogura CMS from Japanese radish, which is the most extensively studied and most widely used. In this review, we discuss Ogura CMS, and other CMS systems, and the causal mitochondrial genes for CMS. Studies on nuclear Rf genes and the cytoplasmic effects of alien cytoplasm on general crop performance are also reviewed. Finally, some of the unresolved questions about CMS are highlighted.