N and P colimitation of N2-fixing and N-supplied fynbos legumes from the Cape Floristic Region

Background and aims

Legume species in the fynbos vegetation of the Cape Floristic Region, that fix N₂ in soils with low P, may have evolved for enhanced acquisition and efficient use of P. It was hypothesized that N₂-fixing and combined-N supplied (N-supplied) A. linearis, P. calyptrata and C. genistoides are adapted to low P and would be relatively unresponsive to increased P of 100 μM.

Methods

18 legume species were evaluated for their nodulation response to low P availability. The N X P interaction was then examined in A. linearis, P. calyptrata and C. genistoides reliant on either N₂-fixation or 300 μM N (NH₄NO₃), and receiving 0.1, 1.0, 10 and 100 μM P (NaH₂PO₄).

Results

In the species selection experiment, A. linearis, P. calyptrata and C. genistoides, with the greatest nodule fresh weight (FW) and nodule FW to root FW ratio, were the most prolific nodulating species. In the N X P experiment, with low P supply, the biomass of N₂-fixing P. calyptrata and C. genistoides was consistently greater than that of N-supplied plants. In contrast, with high P supply of 100 μM P, all N-supplied plants accumulated more biomass than the corresponding N₂-fixing plants. High P-use efficiency, poor down-regulation of P uptake and P storage was evident in A. linearis and P. calyptrata.

Conclusion

The growth response to P and the significant N X P interactions indicate that N₂-fixing and N-supplied plants were not adapted to low P, but rather colimited by both N and P.     

A PATO-compliant zebrafish screening database (MODB): management of morpholino knockdown screen information

Background  

The zebrafish is a powerful model vertebrate amenable to high throughput in vivo genetic analyses. Examples include reverse genetic screens using morpholino knockdown, expression-based screening using enhancer trapping and forward genetic screening using transposon insertional mutagenesis. We have created a database to facilitate web-based distribution of data from such genetic studies.     

Finishing the finished human chromosome 22 sequence

Background

Although the human genome sequence was declared complete in 2004, the sequence was interrupted by 341 gaps of which 308 lay in an estimated approximately 28 Mb of euchromatin. While these gaps constitute only approximately 1% of the sequence, knowledge of the full complement of human genes and regulatory elements is incomplete without their sequences.

Results

We have used a combination of conventional chromosome walking (aided by the availability of end sequences) in fosmid and bacterial artificial chromosome (BAC) libraries, whole chromosome shotgun sequencing, comparative genome analysis and long PCR to finish 8 of the 11 gaps in the initial chromosome 22 sequence. In addition, we have patched four regions of the initial sequence where the original clones were found to be deleted, or contained a deletion allele of a known gene, with a further 126 kb of new sequence. Over 1.018 Mb of new sequence has been generated to extend into and close the gaps, and we have annotated 16 new or extended gene structures and one pseudogene.

Conclusion

Thus, we have made significant progress to completing the sequence of the euchromatic regions of human chromosome 22 using a combination of detailed approaches. Our experience suggests that substantial work remains to close the outstanding gaps in the human genome sequence.     

FLAGELLAR ROOTS AND THE RESERVOIR CYTOSKELETON OF COLACIUM LIBELLAE (EUGLENOPHYCEAE)1

The three flagellar roots of Colacium Ehrenberg give rise to the three microtublar bands of the reservoir cytoskeleton. The dorsal root (DR) originates at the basal body (bb1) of the emergent flagellum. It is initiated on the left side of the cell, runs toward the right side under the posterior end of the reservoir and thence anteriorly in a spiral path over the dorsal surface of the reservoir until it terminates on the left side of the eyespot. Along its length, it appears to initiate a dorsal band (DB) which forms the major dorsal portion of the reservoir cytoskeleton—the dorsal microtubules (DMT). Two roots originate at the basal body (bb2) of the non-emergent flagellum. The ventral root (VR) runs up the left side of the cell and initiates the band of microtubules which forms part of the presumptive vestigial cytopharynx. Therefore, it forms the reinforcing microtubules (MTR) of Colacium. The intermediate root (IR) forms the para-reservoir microtubules (PMT). Flagellar root correlation with the reservoir cytoskeletal bands strengthens their homologies with the bodonid bands and further supports the hypothesis that the euglenoids are derived from the kinetoplastid flagellates.