Pongamia (Millettia pinnata) is a promising biofuel crop with multiple merits. Breeding of ideal Pongamia germplasm for industrial application demands substantial progress in molecular biology of this legume species, which has been largely hampered by the paucity of its genomic data. In this study, we constructed and characterized a comprehensive seed transcriptome by the high-throughput Illumina sequencing technology. We obtained over 83 million high-quality reads, which were processed and assembled into 53,586 unigenes with a mean length of 787 bp. Among these unigenes, 39,602 (73.90 %) and 24,078 (44.93 %) showed significant similarity to proteins in the NCBI non-redundant and the SwissProt protein databases, respectively. Of the annotated unigenes, 30,619 (57.14 %) were classified into 56 Gene Ontology categories. Furthermore, 21,905 (40.88 %) unigenes were assigned to 128 pathways in the Kyoto Encyclopedia of Genes and Genomes pathway database. A set of 364 unigenes involved in five pathways closely related to oil biosynthesis and accumulation were screened out as candidates for future functional analyses. On the other hand, 5710 expressed sequence tag-simple sequence repeats (EST-SSRs) were identified in 4951 unigenes with a density of one SSR every 7.39-kb sequence. One hundred EST-SSRs were randomly selected to validate amplification and to assess polymorphism among 12 Pongamia individuals. Eighty-two primer pairs successfully amplified DNA fragments and 17 of them detected polymorphism, in which the polymorphism information content values ranged from 0.14 to 0.57. Jianzi Huang and Xiaohuan Guo have contributed equally to this work.Electronic supplementary material The online version of this article (

BackgroundPongamia (Millettia pinnata syn. Pongamia pinnata), an oilseed legume species, is emerging as potential feedstock for sustainable biodiesel production. Breeding Pongamia for favorable traits in commercial application will rely on a comprehensive understanding of molecular mechanism regulating oil accumulation during its seed development. To date, only limited genomic or transcript sequences are available for Pongamia, while a temporal transcriptome profiling of developing seeds is still lacking in this species.ResultsIn this work, we conducted a time-series analysis of morphological and physiological characters, oil contents and compositions, as well as global gene expression profiles in developing Pongamia seeds. Firstly, three major developmental phases were characterized based on the combined evidences from embryonic shape, seed weight, seed moisture content, and seed color. Then, the gene expression levels at these three phases were quantified by RNA-Seq analyses with three biological replicates from each phase. Nearly 94% of unigenes were expressed at all three phases, whereas only less than 2% of unigenes were exclusively expressed at one of these phases. A total of 8881 differentially expressed genes (DEGs) were identified between phases. Furthermore, the qRT-PCR analyses for 10 DEGs involved in lipid metabolism demonstrated a good reliability of our RNA-Seq data in temporal gene expression profiling. We observed a dramatic increase in seed oil content from the embryogenesis phase to the early seed-filling phase, followed by a steady and moderate increase towards the maximum at the desiccation phase. We proposed that a highly active expression of most genes related to fatty acid (FA) and triacylglycerol (TAG) biosynthesis at the embryogenesis phase might trigger both the substantial oil accumulation and the membrane lipid synthesis for rapid cell proliferation at this phase, while a concerted reactivation of TAG synthesis-related genes at the desiccation phase might further promote storage lipid synthesis to achieve the maximum content of seed oils.ConclusionsThis study not only built a bridge between gene expression profiles and oil accumulation in developing seeds, but also laid a foundation for future attempts on genetic engineering of Pongamia varieties to acquire higher oil yield or improved oil properties for biofuel applications.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1356-8) contains supplementary material, which is available to authorized users.

Pongamia (Millettia pinnata syn. Pongamia pinnata) is a multipurpose biofuel tree which can withstand a variety of abiotic stresses. Commercial applications of Pongamia trees may substantially benefit from improvements in their oil-seed productivity, which is governed by complex regulatory mechanisms underlying seed development. MicroRNAs (miRNAs) are important molecular regulators of plant development, while relatively little is known about their roles in seed development, especially for woody plants. In this study, we identified 236 conserved miRNAs within 49 families and 143 novel miRNAs via deep sequencing of Pongamia seeds sampled at three developmental phases. For these miRNAs, 1327 target genes were computationally predicted. Furthermore, 115 differentially expressed miRNAs (DEmiRs) between successive developmental phases were sorted out. The DEmiR-targeted genes were preferentially enriched in the functional categories associated with DNA damage repair and photosynthesis. The combined analyses of expression profiles for DEmiRs and functional annotations for their target genes revealed the involvements of both conserved and novel miRNA-target modules in Pongamia seed development. Quantitative Real-Time PCR validated the expression changes of 15 DEmiRs as well as the opposite expression changes of six targets. These results provide valuable miRNA candidates for further functional characterization and breeding practice in Pongamia and other oilseed plants.

Nd 3+ /Zr 4+ -cosubstituted bismuth titanate (BNTZ x , x = 0, 0.05, 0.1, 0.3, and 0.5) thin films have been fabricated by chemical solution deposition and their polarization hysteresis loops, leakage current, and capacitance butterfly loops investigated. Results show that, at Zr content of x = 0.1, both capacitance and remanent polarization can be greatly improved. The BNTZ 0.1 film also exhibits fatigue-free, excellent leakage current characteristics (I % 9.44 9 10 À9 A) at applied voltage of 3 V. High-quality c-axis-oriented BNTZ x = 0.1 films with improved electrical properties were fabricated; this finding supports the feasibility of engineering polarization rotation in ferroelectric bismuth titanate (as suggested theoretically by Roy et al. in Appl. Phys. Lett. 102:182901, 2013).