TABLE 6.

Results of two codon-based tests for positive selection in five symbiotic megaplasmid genes of Sinorhizobium meliloti

RepliconLocusAllelic combinationZ statisticaP value by Fisher's exact testb
pSymAadeC36 × 231.715*0.398
14 × 231.763*0.398
nodC3 × 92.076*0.298
3 × 341.800*0.403
5 × 92.396**0.220
5 × 342.068*0.298
9 × 342.396**0.220
28 × 292.021*0.303
SMa01988 × 111.774*0.362
8 × 231.797*0.359
8 × 282.032*0.551
11 × 281.780*0.359
23 × 281.844*0.359
pSymBidhA1 × 31.847*0.421
1 × 51.747*0.421
1 × 61.784*0.421
3 × 91.837*0.421
3 × 121.783*0.421
3 × 221.807*0.421
5 × 91.735*0.421
5 × 121.711*0.421
5 × 221.813*0.421
6 × 91.790*0.421
6 × 121.789*0.421
6 × 221.767*0.421
pdh12 × 161.747*0.421
17 × 231.756*0.421
17 × 261.773*0.421
  • a Z statistics for all other pSymA loci (fixK, napB, and nifD), pSymB loci (catC, dak, dgoA, and gabT), and other allelic combinations (of the loci shown) were not statistically significant. Asterisks correspond to levels of significance: *, P < 0.05; **, P < 0.01.

  • b The following hypotheses were tested: Ho: dN = dS and HA: dN > dS.