BackgroundSeveral lines of evidence indicate that polyploidy occurred by around 54 million years ago, early in the history of legume evolution, but it has not been known whether this event was confined to the papilionoid subfamily (Papilionoideae; e.g. beans, medics, lupins) or occurred earlier. Determining the timing of the polyploidy event is important for understanding whether polyploidy might have contributed to rapid diversification and radiation of the legumes near the origin of the family; and whether polyploidy might have provided genetic material that enabled the evolution of a novel organ, the nitrogen-fixing nodule. Although symbioses with nitrogen-fixing partners have evolved in several lineages in the rosid I clade, nodules are widespread only in legume taxa, being nearly universal in the papilionoids and in the mimosoid subfamily (e.g., mimosas, acacias) – which diverged from the papilionoid legumes around 58 million years ago, soon after the origin of the legumes.Methodology/Principal FindingsUsing transcriptome sequence data from Chamaecrista fasciculata, a nodulating member of the mimosoid clade, we tested whether this species underwent polyploidy within the timeframe of legume diversification. Analysis of gene family branching orders and synonymous-site divergence data from C. fasciculata, Glycine max (soybean), Medicago truncatula, and Vitis vinifera (grape; an outgroup to the rosid taxa) establish that the polyploidy event known from soybean and Medicago occurred after the separation of the mimosoid and papilionoid clades, and at or shortly before the Papilionoideae radiation.ConclusionsThe ancestral legume genome was not fundamentally polyploid. Moreover, because there has not been an independent instance of polyploidy in the Chamaecrista lineage there is no necessary connection between polyploidy and nodulation in legumes. Chamaecrista may serve as a useful model in the legumes that lacks a paleopolyploid history, at least relative to the widely studied papilionoid models.

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In G2 peas (Pisum sativum L.) apical senescence occurs only in long days (LD), and indeterminate growth is associated with elevated gibberellin (GA) levels in the shoot in short days (SD). Metabolism of GA12 aldehyde was investigated by feeding shoots grown in SD or LD with I"CiGA,2 aldehyde through the cut end of the stem for 0.5 to 6 hours in the light and analyzing the tissue extract by high performance liquid chromatography. More radioactive products were detected than can be accounted for by the two GA metabolic pathways previously known to be present in peas. Three of the major products appear to be GA conjugates, but an additional pathway(s) of GA metabolism may be present. The levels of putative C20 GAs, '4CiGAs3, 4qC]GA44, ['4CJGA,,, and/or I'4C1 GA17, were all elevated in SD as compared to LD. Putative 114CIGA, was slightly higher in LD than in SD. Putative I'4C]GAs3 was a major metabolite after 30 minutes of treatment in SD but had declined after longer treatment times to be replaced by elevated levels of putative I'4C] GA44 and 114CIGA9/,,1. Metabolism of GA2o was slow in both photoperiods. Although GA2o and GA,9 are the major endogenous GAs as determined by gas chromatography-mass spectrometry, putative j'4CJGA20 and I'4CIGA,, were never major products of I'4C]GA,2 aldehyde metabolism. Thus, photoperiod acts in G2 peas to change the rate of GA53 production from GA12 aldehyde, with the levels of the subsequent GAs on the 13-OH pathway being determined by the amount of GA53 being produced.In the G2 genetic line of peas (Pisum sativum L.) senescence of the apical bud, which is a prelude to the senescence of the whole plant, takes place only in long photoperiods (17). In short photoperiods growth is indeterminate. The prevention of senescence by SD is associated with the presence of an elevated level

Expanding legume research beyond the model members of the subfamily Papilionoideae (papilionoids) is necessary if we wish to capture more of the diversity of the enormous, economically important legume family. Chamaecrista fasciculata is emerging as a nonpapilionoid model, belonging to the paraphyletic subfamily Caesalpinioideae within the mimosoid clade. Mimosoids diverged from the common ancestor of soybean (Glycine max), Medicago truncatula, and Lotus japonicus nearly 60 million years ago-nearly contemporaneously with the origin of legumes. There is growing interest within the legume community in C. fasciculata as a complementary legume model for a number of reasons, including phylogenetic position, nodulation within a clade of limited nodulating species, nonpapilionoid floral morphology, herbaceous growth habit, and tractability in laboratory and field settings. Whole-transcriptome sequencing (WTS) of C. fasciculata shoots, roots, and nodules, along with gene expression and single nucleotide polymorphism (SNP) profiling, provides community resources to address fundamental questions about legume evolution. A range of ecotypes, development of functional genomics tools, and an integration of research and undergraduate education leverage these genomic resources.