Ticarcillin degradation product thiophene acetic acid is a novel auxin analog that promotes organogenesis in tomato.

Efficient regeneration of transgenic plants from explants after transformation is one of the crucial steps in developing genetically modified plants with desirable traits. Identification of novel plant growth regulators and developmental regulators will assist to enhance organogenesis in culture. In this study, we observed enhanced shoot regeneration from tomato cotyledon explants in culture media containing timentin, an antibiotic frequently used to prevent Agrobacterium overgrowth after transformation. Comparative transcriptome analysis of explants grown in the presence and absence of timentin revealed several genes previously reported to play important roles in plant growth and development, including Auxin Response Factors (ARFs), GRF Interacting Factors (GIFs), Flowering Locus T (SP5G), Small auxin up-regulated RNAs (SAUR) etc. Some of the differentially expressed genes were validated by quantitative real-time PCR. We showed that ticarcillin, the main component of timentin, degrades into thiophene acetic acid (TAA) over time. TAA was detected in plant tissue grown in media containing timentin. Our results showed that TAA is indeed a plant growth regulator that promotes root organogenesis from tomato cotyledons in a manner similar to the well-known auxins, indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA). In combination with the cytokinin 6-benzylaminopurine (BAP), TAA was shown to promote shoot organogenesis from tomato cotyledon in a concentration-dependent manner. To the best of our knowledge, the present study reports for the first time demonstrating the function of TAA as a growth regulator in a plant species. Our work will pave the way for future studies involving different combinations of TAA with other plant hormones which may play an important role in in vitro organogenesis of recalcitrant species. Moreover, the differentially expressed genes and long noncoding RNAs identified in our transcriptome studies may serve as contender genes for studying molecular mechanisms of shoot organogenesis.

Transcriptome Profiling and Functional Validation of RING-Type E3 Ligases in Halophyte Sesuvium verrucosum under Salinity Stress.

Owing to their sessile nature, plants have developed a tapestry of molecular and physiological mechanisms to overcome diverse environmental challenges, including abiotic stresses. Adaptive radiation in certain lineages, such as Aizoaceae, enable their success in colonizing arid regions and is driven by evolutionary selection. Sesuvium verrucosum (commonly known as Western sea-purslane) is a highly salt-tolerant succulent halophyte belonging to the Aizoaceae family; thus, it provides us with the model-platform for studying plant adaptation to salt stress. Various transcriptional and translational mechanisms are employed by plants to cope with salt stress. One of the systems, namely, ubiquitin-mediated post-translational modification, plays a vital role in plant tolerance to abiotic stress and other biological process. E3 ligase plays a central role in target recognition and protein specificity in ubiquitin-mediated protein degradation. Here, we characterize E3 ligases in Sesuvium verrucosum from transcriptome analysis of roots in response to salinity stress. Our de novo transcriptome assembly results in 131,454 transcripts, and the completeness of transcriptome was confirmed by BUSCO analysis (99.3% of predicted plant-specific ortholog genes). Positive selection analysis shows 101 gene families under selection; these families are enriched for abiotic stress (e.g., osmotic and salt) responses and proteasomal ubiquitin-dependent protein catabolic processes. In total, 433 E3 ligase transcripts were identified in S. verrucosum; among these transcripts, single RING-type classes were more abundant compared to multi-subunit RING-type E3 ligases. Additionally, we compared the number of single RING-finger E3 ligases with ten different plant species, which confirmed the abundance of single RING-type E3 ligases in different plant species. In addition, differential expression analysis showed significant changes in 13 single RING-type E3 ligases (p-value < 0.05) under salinity stress. Furthermore, the functions of the selected E3 ligases genes (12 genes) were confirmed by yeast assay. Among them, nine genes conferred salt tolerance in transgenic yeast. This functional assay supports the possible involvement of these E3 ligase in salinity stress. Our results lay a foundation for translational research in glycophytes to develop stress tolerant crops.

The genome of pest Rhynchophorus ferrugineus reveals gene families important at the plant-beetle interface.

The red palm weevil, Rhynchophorus ferrugineus, infests palm plantations, leading to large financial losses and soil erosion. Pest-host interactions are poorly understood in R. ferrugineus, but the analysis of genetic diversity and pest origins will help advance efforts to eradicate this pest. We sequenced the genome of R. ferrugineus using a combination of paired-end Illumina sequencing (150 bp), Oxford Nanopore long reads, 10X Genomics and synteny analysis to produce an assembly with a scaffold N50 of ~60 Mb. Structural variations showed duplication of detoxifying and insecticide resistance genes (e.g., glutathione S-transferase, P450, Rdl). Furthermore, the evolution of gene families identified those under positive selection including one glycosyl hydrolase (GH16) gene family, which appears to result from horizontal gene transfer. This genome will be a valuable resource to understand insect evolution and behavior and to allow the genetic modification of key genes that will help control this pest.

Prospects for the Study and Improvement of Abiotic Stress Tolerance in Date Palms in the Post-genomics Era.

Date palm (Phoenix dactylifera L.) is a socio-economically important crop in the Middle East and North Africa and a major contributor to food security in arid regions of the world. P. dactylifera is both drought and salt tolerant, but recent water shortages and increases in groundwater and soil salinity have threatened the continued productivity of the crop. Recent studies of date palm have begun to elucidate the physiological mechanisms of abiotic stress tolerance and the genes and biochemical pathways that control the response to these stresses. Here we review recent studies on tolerance of date palm to salinity and drought stress, the role of the soil and root microbiomes in abiotic stress tolerance, and highlight recent findings of omic-type studies. We present a perspective on future research of abiotic stress in date palm that includes improving existing genome resources, application of genetic mapping to determine the genetic basis of variation in tolerances among cultivars, and adoption of gene-editing technologies to the study of abiotic stress in date palms. Development of necessary resources and application of the proposed methods will provide a foundation for future breeders and genetic engineers aiming to develop more stress-tolerant cultivars of date palm.

Genomic Insights into Date Palm Origins.

With the development of next-generation sequencing technology, the amount of date palm (Phoenix dactylifera L.) genomic data has grown rapidly and yielded new insights into this species and its origins. Here, we review advances in understanding of the evolutionary history of the date palm, with a particular emphasis on what has been learned from the analysis of genomic data. We first record current genomic resources available for date palm including genome assemblies and resequencing data. We discuss new insights into its domestication and diversification history based on these improved genomic resources. We further report recent discoveries such as the existence of wild ancestral populations in remote locations of Oman and high differentiation between African and Middle Eastern populations. While genomic data are consistent with the view that domestication took place in the Gulf region, they suggest that the process was more complex involving multiple gene pools and possibly a secondary domestication. Many questions remain unanswered, especially regarding the genetic architecture of domestication and diversification. We provide a road map to future studies that will further clarify the domestication history of this iconic crop.

Genome-wide evidence for efficient positive and purifying selection in Capsella grandiflora, a plant species with a large effective population size.

Recent studies comparing genome-wide polymorphism and divergence in Drosophila have found evidence for a surprisingly high proportion of adaptive amino acid fixations, but results for other taxa are mixed. In particular, few studies have found convincing evidence for adaptive amino acid substitution in plants. To assess the generality of this finding, we have sequenced 257 loci in the outcrossing crucifer Capsella grandiflora, which has a large effective population size and low population structure. Using a new method that jointly infers selective and demographic effects, we estimate that 40% of amino acid substitutions were fixed by positive selection in this species, and we also infer a low proportion of slightly deleterious amino acid mutations. We contrast these estimates with those for a similar data set from the closely related Arabidopsis thaliana and find significantly higher rates of adaptive evolution and fewer nearly neutral mutations in C. grandiflora. In agreement with results for other taxa, genes involved in reproduction show the strongest evidence for positive selection in C. grandiflora. Taken together, these results imply that both positive and purifying selection are more effective in C. grandiflora than in A. thaliana, consistent with the contrasting demographic history and effective population sizes of these species.