Project description:The transition to flowering is characterized by a shift of the shoot apical meristem (SAM) from leaf production to the initiation of a floral meristem. In this study, we addressed the nature of SAM gene networks involved in the early floral initiation process in the crop legume soybean. Unique aspects (such as pod development and nitrogen fixation) of legume development make them appealing for plant development studies. Soybean, a major oilseed crop, possesses varied maturity groups; hence, understanding and unravelling initial transition control has implications in manipulating crop yield. To this end, we performed global gene expression analysis using Affymetrix® soybean GeneChip® with RNA isolated from micro-dissected soybean SAMs at various time points after plants were shifted from long-day to short-day growth conditions. Analysis of the resulting microarray data revealed a total of 331 transcripts that have differential expression profiles. Intriguingly, about 20% of the transcripts affected by the switch in the development program have orthologs reported to be responsive to abscisic acid (ABA), suggesting an increase in ABA levels in the SAM during this developmental change. A subsequent immunoassay verified this, thereby implicating its possible function as an endogenous signal during the floral evocation process. The striking occurrence of abiotic stress-related transcripts, including trehalose metabolism genes, in SAMs during the early transition to floral meristems points to an overlap of abiotic stress and floral signalling pathways in soybean. In addition, other hormones - auxin, jasmonic acid and brassinosteroids - and a number of candidate protein kinases may also act in the signalling process prior to or concurrently with the induction of the putative floral homeiotic transcripts. This indicates that molecular events mediated by multiple hormonal pathways are part of the mechanism employed by soybean to regulate the floral transition process. Keywords: transcript profiling floral transition soybean shoot apical meristem

Project description:Molecular characterization of leaf development has not been well studied in soybean. Studies have shown that genomic regions controlling multifoliate leaf morphology in Glycine max also regulates important agronomic characters including yield, seed weight, seed number, shattering, plant growth, and flowering. Two soybean isolines that differed in leaf phenotype were profiled by high throughput RNA and small RNA (sRNA) sequencing. A Clark isoline, homozygous for a dominant mutant allele, Lf1, that specifies a five-foliate compound leaf was compared to wild type Clark that is homozygous for the standard allele that produces trifoliate leaves. Although Lf1 is dominant, it presents variable expressivity as the young plantlets with the Lf1Lf1 genotype initially have trifoliate leaves in the first few weeks, after which they transition to five-foliate leaves. At later developmental stages, they begin to produce four-foliate or trifoliate leaves. In RNA-Seq experiments, a total of 91 and 95 million reads were generated in each lane of Illumina sequencing for the shoot tip of wild type Clark standard (CS) and mutant Clark five-foliate (CF) libraries, respectively. Of these, ~70% million reads aligned to the 78,743 target Glyma models from the reference soybean genome (cv. Williams 82) with maximum of 3 mismatches and up to 25 alignments. Where as in vegetative bud, 56 (CS) to 59 (CF) million reads were produced and of these ~80% aligned to the soybean reference genome. The comparative studies of the transcript profiles of the wild-type versus mutant line revealed a number of differentially expressed genes. A total of 1,296 and 2,083 genes were up-regulated in the shoot tip of CS and CF, respectively that showed ≥2-fold expression difference. On the contrary in the vegetative bud, much smaller number of genes 14 (CS) and 94 (CF) showed increased transcript abundance. In sRNA analysis, a collection of 200,447 and 268,508 unique sRNA sequences isolated from shoot tip tissue of CS and CF were aligned to the soybean reference genome and their target glyma models were predicted using bioinformatics. This sRNA analysis at genome level reveals differences in size distribution of classes in the CS and CF. This study provides insight into the initial understanding of leaf development in soybean by revealing a number of genes and sRNAs differentially expressed between the CS and CF.

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Glycine max

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