Vaidehi Patel

The coding regions of two genes (qa-2 and qa-3) in the qa gene cluster of Neurospora crassa have been localized by nucleotide sequence analysis combined with data on previously determined NH2-terminal amino acid sequences for the proteins that these genes encode. The start point of transcription for each of these genes has been determined by nuclease S1 mapping experiments with poly(A)+RNA isolated from quinic acid-induced cultures of N. crassa. The sequences of approximately 200 nucleotides 5' to the start point of transcription have been compared with each other and with those of other eukaryotes. The results show that neither of these regions for the qa-2 nor the qa-3 genes share any significant homology with sequences apparently conserved in higher eukaryotic promoters (-25 and -70 regions). However, the qa-2 and qa-3 sequences do show homology with each other in these regions. Comparison of the 5'-flanking regions of these Neurospora genes with those of several Saccharomyces cerevisiae genes reveals a number of similarities in the region preceding the translation initiation codons.

A transcription map of the qa gene cluster of Neurospora crassa has been constructed by using cloned DNA fragments as hybridization probes. The mRNAs encoded in the previously identified qa-2 (3-dehydroquinate hydro-lyase, EC 4.2.1.10), qa-4 (dehydroshikimate dehydratase), qa-3 (quinate:NAD+ 3-oxidoreductase, EC 1.1.1.24), and qa-1 (regulatory protein) genes have been characterized. In addition, mRNAs encoded in two new genes in this cluster (qa-x, qa-y) have been identified. Regulation of this system occurs at the level of transcription and is under the combined control of quinic acid and the qa-1 protein. The qa cluster represents a group of adjacent coding sequences which occupy approximately 18 kilobases in linkage group VII. The expression of the qa-1 gene appears to be constitutive but also autoregulated. mRNAs encoded in genes flanking the qa gene cluster have also been identified.

Heritable symbionts are common in terrestrial arthropods and often provide beneficial services to hosts. Unlike obligate, nutritional symbionts that largely persist under strict host control within specialized host cells, heritable facultative symbionts exhibit large variation in within-host lifestyles and services rendered with many retaining the capacity to transition among roles. One enigmatic symbiont, Candidatus Fukatsuia symbiotica, frequently infects aphids with reported roles ranging from pathogen, defensive symbiont, mutualism exploiter, and nutritional co-obligate symbiont. Here, we used an in vitro culture-assisted protocol to sequence the genome of a facultative strain of Fukatsuia from pea aphids (Acyrthosiphon pisum). Phylogenetic and genomic comparisons indicate that Fukatsuia is an aerobic heterotroph, which together with Regiella insecticola and Hamiltonella defensa form a clade of heritable facultative symbionts within the Yersiniaceae (Enterobacteriales). These three heritable facultative symbionts largely share overlapping inventories of genes associated with housekeeping functions, metabolism, and nutrient acquisition, while varying in complements of mobile DNA. One unusual feature of Fukatsuia is its strong tendency to occur as a coinfection with H. defensa. However, the overall similarity of gene inventories among aphid heritable facultative symbionts suggests that metabolic complementarity is not the basis for coinfection, unless playing out on a H. defensa strain-specific basis. We also compared the pea aphid Fukatsuia with a strain from the aphid Cinara confinis (Lachninae) where it is reported to have transitioned to co-obligate status to support decaying Buchnera function. Overall, the two genomes are very similar with no clear genomic signatures consistent with such a transition, which suggests co-obligate status in C. confinis was a recent event.