Development and crosstransferability of functionally relevant microsatellite markers in Dendrocalamus latiflorus and related bamboo species

Genome survey sequencing-based SSR marker development and their validation in Dendrocalamus longispathus

Bamboo is an important genetic resource in India, supporting rural livelihood and industries. Unfortunately, most Indian bamboo taxa are devoid of basic genomic or marker information required to comprehend the genetic processes for further conservation and management. In this study, we perform genome survey sequencing for development of de novo genomic SSRs in Dendrocalamus longispathus, a socioeconomically important bamboo species of northeast India. Using Illumina platform, 69.49 million raw reads were generated and assembled into 1,145,321 contig with GC content 43% and N50 1228 bp. In total, 46,984 microsatellite repeats were mined-out wherein di-nucleotide repeats were most abundant (54.71%) followed by mono- (31.91%) and tri-repeats (9.85%). Overall, AT-rich repeats were predominant in the genome, but GC-rich motifs were more frequent in tri-repeats. Afterwards, 21,596 SSR loci were successfully tagged with the primer pairs, and a subset of 50 were validated through polymerase chain reaction amplification. Of these, 36 SSR loci were successfully amplified, and 16 demonstrated polymorphism. Using 13 polymorphic SSRs, a moderate level of gene diversity (He = 0.480; Ar = 3.52) was recorded in the analysed populations of D. longispathus. Despite the high gene flow (Nm = 4.928) and low genetic differentiation (F_ST = 0.119), severe inbreeding (F_IS = 0.407) was detected. Further, genetic clustering and STRUCTURE analysis revealed that the entire genetic variability is captured under two major gene pools. Conclusively, we present a comprehensive set of novel SSR markers in D. longispathus as well as other taxa of tropical woody bamboos.

Assessment of genetic diversity and population structure in wild Ziziphus species from northwest India using SSR marker technique

BACKGROUND

Ziziphus species particularly Ziziphus mauritiana and Ziziphus nummularia constitute an important part of genetic resources in India. They contribute economically as a fruit crop with lots of morphological and pomological variability. In current study, 48 accessions belonging to two wild Ziziphus species, i.e., Z. mauritiana and Z. nummularia, were characterized using SSR markers. In addition, external features were also examined using stereomicroscope.

RESULTS

Present investigation was done to explore the genetic structure of North Indian jujube. In total, 23 SSR markers detected 57 SSR alleles with an average of 2.47 alleles. Highest number of alleles (4) were detected by three primers, namely BFU1178, BFU479, and ZCMS14, while lowest number of alleles (2) were detected by fifteen primers. Highest Polymorphism Information Content (PIC) was 0.500 and shown by two primers, namely BFU528 and BFU1248, while lowest PIC (0.041) was observed in primers BFU286 with mean value of 0.443. Similarly, highest value of marker index (MI) was detected by primer BFU1178 i.e. 1.969, and lowest value of marker index was observed in primer BFU286 i.e. 0.021. Dendrogram generated using SSR markers data and principal component analysis showed two major groups of the analyzed germplasm with intermixing. STRUCTURE analysis also clustered all the accessions into two groups. We did not found correlation between geographic and genetic distances.

CONCLUSIONS

The preliminary results suggest that there is high level of gene pool mixing in these species which can be attributed to their cross-pollination habit. However, more such studies with large numbers of samples are required in future to gain concrete insights of the genetic structure in these species.

Development and characterization of bZIP transcription factor based SSRs in wheat

Assessment of existing diversity is the key for germplasm conservation and crop improvement. Wheat (Triticum aestivum L.) is among the most important cereal crop and consumed by two billion world's populations. DNA-based markers are predominantly used for diversity characterization because they are easy to develop and not influenced by environment. Among them microsatellites (simple sequence repeats, SSRs) are most suitable due to their genome-wide distribution, hypervariability and reproducibility for their applications in diversity, genetic improvement, and molecular breeding. bZIP transcription factors play major roles in plants in light and stress signalling, seed development, and defence. A total of 846 SSRs were identified from 370 wheat cDNA sequences and a sub-set of 35 polymorphic TabZIPMS (TriticumaestivumbZIP MicroSatellites) was used for diversity and genetic structure analysis of 92 Indian wheat varieties and related species. 114 SSR variants ranging from 2 to 5 per SSR locus were detected for 35 SSRs in the varieties. Average polymorphic information content (PIC) and observed heterozygosity was found to be 0.135 and 0.838, respectively. Thirty-four SSRs showed cross-transferability into different related species. Combined Bayesian model and Jaccard's similarity based genetic clustering analysis revealed two clusters of 80 bread wheat varieties and one separate cluster of related species. In this study, a total 35 novel bZIP-derived SSRs were identified in a set 370 bZIP genes and shown high polymorphism and cross-species transferability in wheat. The findings provide resources for future utilization in genetic resource conservation, trait introgression, breeding and varietal development.

Genetic diversity and structure of Dendrocalamus hamiltonii natural metapopulation: a commercially important bamboo species of northeast Himalayas

Dendrocalamus hamiltonii is a commercially important bamboo species of India, experiencing population depletion due to heavy extraction from natural forests. Nuclear simple sequence repeats (nSSRs) were used to study the genetic diversity and population genetic structure of 19 natural stands of D. hamiltonii distributed across the northeast Himalayas. A total of 68 nSSR primer pairs of D. latiflorus and Bambusa arundinacea have been tested in D. hamiltonii for their transferability, out of which 17 primers showing positive and polymorphic amplification were used for genotyping. A total of 130 alleles were generated in 535 individuals of all the populations using selected primer pairs. The marker analysis indicated that D. hamiltonii populations have maintained a low level of genetic diversity (h = 0.175, I = 0.291) in northeastern region of India. Despite a large proportion of the genetic variation (83.47%) confined within the populations, a moderate level of genetic differentiation (F _ST = 0.165) was observed among the populations. The clustering pattern obtained in UPGMA and STRUCTURE analysis revealed that most of the populations were clustered in accordance with their geographical distribution. Two populations (DH03 and DH13) exhibiting significant genetic admixture were identified and recommended for in situ conservation. In addition, six highly diverse populations were also suggested for conservation in different geographical area under study. The study has revealed useful nSSR markers for D. hamiltonii, which were lacking earlier and the information generated herein is of paramount importance in devising programs for species conservation and genetic improvement.

Genome-Wide Transcriptional Profiling to Elucidate Key Candidates Involved in Bud Burst and Rattling Growth in a Subtropical Bamboo (Dendrocalamus hamiltonii)

Bamboo, one of the fastest growing plants, can be a promising model system to understand growth. The study provides an insight into the complex interplay between environmental signaling and cellular machineries governing initiation and persistence of growth in a subtropical bamboo (Dendrocalamus hamiltonii). Phenological and spatio-temporal transcriptome analysis of rhizome and shoot during the major vegetative developmental transitions of D. hamiltonii was performed to dissect factors governing growth. Our work signifies the role of environmental cues, predominantly rainfall, decreasing day length, and high humidity for activating dormant bud to produce new shoot, possibly through complex molecular interactions among phosphatidylinositol, calcium signaling pathways, phytohormones, circadian rhythm, and humidity responses. We found the coordinated regulation of auxin, cytokinin, brassinosteroid signaling and cell cycle modulators; facilitating cell proliferation, cell expansion, and cell wall biogenesis supporting persistent growth of emerging shoot. Putative master regulators among these candidates were identified using predetermined Arabidopsis thaliana protein-protein interaction network. We got clues that the growth signaling begins far back in rhizome even before it emerges out as new shoot. Putative growth candidates identified in our study can serve in devising strategies to engineer bamboos and timber trees with enhanced growth and biomass potentials.