Assessment of Fruit Drop in Different Cultivars of Litchi

Individual panicles produce hundreds of pistillate flowers but only a small proportion of these bear fruit and reach maturity. There are some stages of fruit drop during growth and development caused by different factors. An experimental trial was conducted in National Active Germplasm Site (NAGS) at ICAR-NRC on Litchi, Muzaffarpur, to assess the fruit drop due to different factors during 2014–2015. The result revealed that four factors viz., improper pollination and fertilization, embryo abortion, seed and fruit borer, and normal fruit abscission were associated with fruit drop in litchi and fruit drop varied from 23.53–77.54% with a maximum in Shahi and lowest in Elaichi during the first week of flowering. Fruit drop increased to 92.65–97.86% during the third week of flowering because of improper pollination and fertilization, and it reached a maximum level of 98.51–99.70% at the time of ripening stage with the lowest in Deshi. Embryo abortion was one primary cause of fruit drop during the 4th week whereas infestation of seed and fruit borer was the major factor for fruit drop during the 5–7th week. Such fruit drop can be controlled by managing the infestation of borer. Abscission due to ethylene production and heat stress during the maturity of fruit was yet another cause of fruit drop. This study will help to researcher to find out the time of infestation of seed and fruit borer which causes heavy fruit drop and it can be controlled with pest management option.

Transcriptomic Analysis Reveals Key Candidate Genes Related to Seed Abortion in Chinese Jujube (Ziziphus jujuba Mill.)

Background: Seed abortion is a common phenomenon in Chinese jujube that seriously hinders the process of cross-breeding. However, the molecular mechanisms of seed abortion remain unclear in jujube. Methods: Here, we performed transcriptome sequencing using eight flower and fruit tissues at different developmental stages in Ziziphus jujuba Mill. ‘Zhongqiusucui’ to identify key genes related to seed abortion. Histological analysis revealed a critical developmental process of embryo abortion after fertilization. Results: Comparisons of gene expression revealed a total of 14,012 differentially expressed genes. Functional enrichment analyses of differentially expressed genes between various sample types uncovered several important biological processes, such as embryo development, cellular metabolism, and stress response, that were potentially involved in the regulation of seed abortion. Furthermore, gene co-expression network analysis revealed a suite of potential key genes related to ovule and seed development. We focused on three types of candidate genes, agamous subfamily genes, plant ATP-binding cassette subfamily G transporters, and metacaspase enzymes, and showed that the expression profiles of some members were associated with embryo abortion. Conclusions: This work generates a comprehensive gene expression data source for unraveling the molecular mechanisms of seed abortion and aids future cross-breeding efforts in jujube.

A novel ERF transcription factor, CmERF12, negatively influences chrysanthemum embryo development

Embryo abortion often occurs during distant hybridization events. Apetala 2/ethylene-responsive factor (AP2/ERF) proteins are key transcription factor (TF) regulators of plant development and stress resistance, but their roles in hybrid embryo development are poorly understood. We isolated a novel AP2/ERF TF, CmERF12, from chrysanthemum and showed that it adversely affects embryo development during distant hybridization. Transcriptome and real-time quantitative PCR data demonstrated that CmERF12 is expressed at significantly higher levels in aborted ovaries compared with normal ovaries. CmERF12 localizes to the cell nucleus and contains a conserved EAR motif that mediates its transcription repressor function in yeast and plant cells. We generated an amiR-CmERF12 transgenic Chrysanthemum morifolium (C.m.) var. ‘Yuhualuoying’ and conducted distant hybridization with the wild-type tetraploid, Chrysanthemum nankingense (C.n.), revealing that CmERF12 knockdown significantly promoted embryo development and increased the seed setting rates during hybridization. The expression of various embryo development-related genes was up-regulated in developing ovaries from the ♀amiR-CmERF12-C.m. × ♂C.n. cross. Furthermore, CmERF12 directly interacted with CmSUF4 and significantly reduced its ability to activate its target gene CmEC1. Overall, we invented an original method to overcome plant distant hybridization barriers and unraveled the mechanism by which CmERF12 negatively affects chrysanthemum embryo development.

The transcription factor CmLEC1 positively regulates the seed-setting rate in hybridization breeding of chrysanthemum

Distant hybridization is widely used to develop crop cultivars, whereas the hybridization process of embryo abortion often severely reduces the sought-after breeding effect. The LEAFY COTYLEDON1 (LEC1) gene has been extensively investigated as a central regulator of seed development, but it is far less studied in crop hybridization breeding. Here we investigated the function and regulation mechanism of CmLEC1 from Chrysanthemum morifolium during its seed development in chrysanthemum hybridization. CmLEC1 encodes a nucleic protein and is specifically expressed in embryos. CmLEC1’s overexpression significantly promoted the seed-setting rate of the cross, while the rate was significantly decreased in the amiR-CmLEC1 transgenic chrysanthemum. The RNA-Seq analysis of the developing hybrid embryos revealed that regulatory genes involved in seed development, namely, CmLEA (late embryogenesis abundant protein), CmOLE (oleosin), CmSSP (seed storage protein), and CmEM (embryonic protein), were upregulated in the OE (overexpressing) lines but downregulated in the amiR lines vs. wild-type lines. Future analysis demonstrated that CmLEC1 directly activated CmLEA expression and interacted with CmC3H, and this CmLEC1–CmC3H interaction could enhance the transactivation ability of CmLEC1 for the expression of CmLEA. Further, CmLEC1 was able to induce several other key genes related to embryo development. Taken together, our results show that CmLEC1 plays a positive role in the hybrid embryo development of chrysanthemum plants, which might involve activating CmLEA’s expression and interacting with CmC3H. This may be a new pathway in the LEC1 regulatory network to promote seed development, one perhaps leading to a novel strategy to not only overcome embryo abortion during crop breeding but also increase the seed yield.

Aneuploid abortion correlates positively with MAD1 overexpression and miR-125b down-regulation

Background Aneuploidy is the most frequent cause of early-embryo abortion. Any defect in chromosome segregation would fail to satisfy the spindle assembly checkpoint (SAC) during mitosis, halting metaphase and causing aneuploidy. The mitotic checkpoint complex (MCC), comprising MAD1, MAD2, Cdc20, BUBR1 and BUB3, plays a vital role in SAC activation. Studies have confirmed that overexpression of MAD2 and BUBR1 can facilitate correct chromosome segregation and embryo stability. Research also proves that miR-125b negatively regulates MAD1 expression by binding to its 3′UTR. However, miR-125b, Mad1 and Bub3 gene expression in aneuploid embryos of spontaneous abortion has not been reported to date. Methods In this study, embryonic villi from miscarried pregnancies were collected and divided into two groups (aneuploidy and euploidy) based on High-throughput ligation-dependent probe amplification (HLPA) and Fluorescence in situ hybridization (FISH) analyses. RNA levels of miR-125b, MAD1 and BUB3 were detected by Quantitative real-time PCR (qRT-PCR); protein levels of MAD1 and BUB3 were analysed by Western blotting. Results statistical analysis (p < 0.05) showed that miR-125b and BUB3 were significantly down-regulated in the aneuploidy group compared to the control group and that MAD1 was significantly up-regulated. Additionally, the MAD1 protein level was significantly higher in aneuploidy abortion villus, but BUB3 protein was only mildly increased. Correlation analysis revealed that expression of MAD1 correlated negatively with miR-125b. Conclusion These results suggest that aneuploid abortion correlates positively with MAD1 overexpression, which might be caused by insufficient levels of miR-125b. Taken together, our findings first confirmed the negative regulatory mode between MAD1 and miR-125b, providing a basis for further mechanism researches in aneuploid abortion.

Crossability Barriers in Interspecific Hybridization of Ricebean [Vigna umbellata (Thunb.) Ohwi and Ohashi] with Other Vigna Species

Background: Ricebean [Vigna umbellata (Thunb.) Ohwi and Ohashi] is a multipurpose grain legume of Mid-Himalayan region mainly cultivated for food, fodder, green manure and has emerged as a good alternative to other pulse crops such as blackgram and greengram which do not flourish in this region due to their susceptibility to cold temperature stress. It is well reported that the nutritional value of ricebean is higher as compared to many other legumes of the Vigna family and has some superior qualities greater than greengram, blackgram and cowpea. It is also resistance to drought, diseases and pests specially the storage pests during growth period and possesses high percentage of seed viability. Despite having all the favourable traits, it is not much popular among the farmers due to the late maturity and indeterminate growth habit. Instead, farmers prefer other crops which fit easily into their cropping pattern and are easy to harvest. A little genetic improvement with respect to maturity and growth habit can revive its cultivation and show great results in its production as a valuable crop. Thus, the present investigation was formulated to introgress desired traits from mash and adzukibean into otherwise high yielding ricebean genotypes using inter-specific hybridization. Methods: The present investigation involves the inter-specific hybridization among three Vigna species viz, ricebean (Vigna umbellata), blackgram (Vigna mungo) and adzukibean (Vigna angularis). In the year 2017, six genotypes of ricebean (RBHP-36, RBHP-38, RBHP-43, RBHP-61, RBHP-107 and RBHP-108) were crossed with two genotypes of blackgram (HimMash-1 and Palampur-93) and one genotype of adzukibean (HPU-51) in glasshouse conditions. Result: The study revealed that successful crosses were possible only between ricebean and blackgram. All the Inter-specific crosses showed very low pod set percentage ranging from 0 -4% and F1 germination percentage ranging from 20-42%. Pod set percentage and pods harvested varied with combinations of two parental cultivars of each species for most of the inter-specific hybrids. The successful pod set was observed in 16 out of 36 inter-specific crosses. Highest crossability was observed in blackgram and ricebean crosses. Crossing of adzukibean with ricebean showed poor or no pod set among the entire cross combinations which are attributed to early embryo abortion and degeneration during embryogenesis.

Transcriptome of peanut kernel and shell reveals the mechanism of calcium on peanut pod development

Calcium is not only a nutrient necessary for plant growth but also a ubiquitous central element of different signaling pathways. Ca2+ deficiency in soil may cause embryo abortion, which can eventually lead to abnormal development of peanut pods during the harvest season. To further study the mechanisms by which Ca2+ affects the shells and kernels of peanuts, transcriptome sequencing was used to explore the genes differentially expressed in shells and kernels during the early stage of peanut pod development between Ca2+ sufficient and deficient treatments. In this study, 38,894 expressed genes were detected. RNA-seq based gene expression profiling showed a large number of genes at the transcriptional level that changed significantly in shells and kernels between the Ca2+ sufficient and deficient treatments, respectively. Genes encoding key proteins involved in Ca2+ signal transduction, hormones, development, ion transport, and nutrition absorption changed significantly. Meanwhile, in the early stage of pod development, calcium first promoted nutrient absorption and development of shells, which has less effect on the formation of seed kernels. These results provide useful information for understanding the relationship between Ca2+ absorption and pod development.

Aneuploid Abortion Positively Correlate With MAD1 Overexpression and mir125b Depression

Background: Aneuploid is the most frequent cause of early embryo abortion, and any defect in chromosome segregation would fail to satisfy spindle assembly checkpoint (SAC) during mitosis, which could lead to the halted metaphase and aneuploid occurrence. Mitotic checkpoint complex(MCC), a complex compound of MAD1、MAD2、Cdc20、BUBR1 and BUB3, plays an important role in SAC activation. Studies have confirmed that the overexpression of MAD2 and BUBR1 can facilitate the correct chromosome segregation and embryo stability. Research identifications also proved that miR-125b negatively regulated MAD1 expression by binding to its 3’UTR. However, the expression of mir125b, MAD1 and BUB3 genes in aneuploidy embryos of spontaneous abortion has not been reported.Methods: In this study, embryonic villi from miscarriage pregnant women were collected and divided into two groups (aneuploidy and euploidy) by HLPA and FISH analysis. The RNA levels of mir125b, MAD1 and BUB3 were detected through QRT-PCR, while Western blot was further used to analyze the protein levels of MAD1 and BUB3.Results: SPSS 17.0 statistical analysis(P<0.05) showed that mir125b and BUB3 were significantly down-regulated in aneuploidy group compared to the control group, MAD1 was significantly up-regulated in RNA level; Additionally, MAD1 protein level was also significantly higher while BUB3 was mildly increased in aneuploidy abortion villus. Correlation analysis revealed that the expression of MAD1 was negatively correlated with Mir125b.Conclusion: these results suggested that aneuploid abortion was positively correlated with MAD1 overexpression which might be caused by insufficient mir125b.