These responses were initially predicted by clustering analysis, as these mutants fall into clusters being predicted involvements in blue light signalling (clusters I, II, IV and V) and those predictions involving blue, red and far-red light signalling (clusters III). These putative components of light signalling in Xcc included three HKs, four GGDEF-characterized

proteins and selleck four hybrid HKs. Motility is an important characteristic for infection in a number of plant pathogenic species (Swings et al., 1993); thus, we tested whether PAS proteins participate in the development of motility in the Xcc in response to variable light conditions. Five of 33 mutants showed significantly modified motility responses to light (Fig. 3). Among them, DLT4313 was increased, and DLT0728, DLT0818 and DLT1965 were decreased in blue light. DLT1036 exhibited decreased motility in blue, red, far-red or white light. These results partially agreed with the results of clustering analysis (Fig. 1c), in which the protein altered in DLT0728 was associated with cluster IV and was a putative blue light–signalling component. Selleckchem STI571 We cultured cabbage infected with Xcc strains under two levels of light intensity. The light intensity reaching into

a leaf was initially estimated in a light transmission assay, which indicated that a light intensity of 4512 and 593 lux reached the middle of a leaf exposed to light sources of 12 000 and 2000 lux, respectively (Fig. S2). The results of Xcc strains are shown in Fig. S3. We also tested rescue strains of three mutants, DLT1036, DLT 2324 and DLT3829. In assays of Xcc strains infecting cabbage, four mutants (DLT3829, DLT1036, DLT2324 and DLT1476) had an effect on light-condition-dependent shifts in bacterial virulence. Leaf-lesion photographs of the four mutants are shown in Fig. 4a (strong light) and 4b (weak light), and the mutants showed different changes in lesion length

(LL) in strong/weak light or between the two light intensities, as shown in Fig. 4c. The relative lesion rate (RLR) values of the four mutants were significantly different from Etomidate wild-type Xcc 8004 (Fig. 4d). The tests of complementary strains are shown in Fig. S4, in which the virulence of pLC1036, pLC2324 and pLC3829 were partially rescued in comparison with either LL or RLR. In addition, three of the four mutants have been shown to be GGDEF-characterized proteins involved in virulence under natural light (Ryan et al., 2007). These data strongly suggest that these PAS proteins are light-signalling components that are vital for Xcc pathogenesis. Some of the PAS proteins in Xcc may have roles as intermediates in photo-signalling pathways other than light sensing, and some of those involved in light signalling may not have phenotypes that could be observed in our screen. Previous studies have suggested that PAS domains sense light, and the subsequent functions result in various responses, for example, a PAS domain can be activated in blue light to regulate B.