| PsPK2 is the pea homologue of the Arabidopsis PINOID (PID) gene that plays an important role in polar auxin transport by targeting auxin efflux carriers, PINS. PsPK2 had 445 amino acids and possessed 12 conserved catalytic subdomains that characterize protein kinases. PsPK2 was strongly expressed in developing regions of wildtype (WT) pea plants, such as shoot tips, immature adult leaves, developing embryos and flower buds. PsPK2 mRNA was found to be more abundant in tendrils than in leaflets of pea leaves, irrespective of genotype, suggesting that it might play a role in the thigmotropic response. PsPK2 was differentially expressed in shoot tips of the different leaf form mutants. PsPK2 mRNA was localized in the tapetal cells and pollen grains; but transiently expressed in the stigma of WT pea flowers. 2.3 kb of the PsPK2 promoter was obtained and was predicted to possess auxin and gibberellin (GA) response elements. Auxin and GA positively regulated PsPK2 expression in pea, and auxin induction of PsPK2 did not require de novo protein synthesis. GUS expression in Arabidopsis shoots of PsPK2::GUS, DR5::GUS and PID::GUS was mainly localized in stipules, hydothodes, veins, developing leaves and cotyledons. Unlike DR5::GUS, PsPK2::GUS and PID: :GUS were not expressed in root tips. Both DR5: :GUS and PsPK2::GUS were induced by different auxins and were more sensitive to MeIAA, 4-Cl-IAA and NAA than others. Cytokinin increased auxin transport in Arabidopsis seedlings. Auxin, GA and cytokinin all increased GUS activity in shoots of PsPK2::GUS transformed plants compared to the control. However, only auxin and GA increased GUS activity in PID::GUS shoots. Overexpression of PsPK2 in Arabidopsis increased root length and reduced apical dominance in the inflorescence and caused defective pollen grains and reduced seed set. pid mutants had less free IAA than WT, but overexpression did not affect free IAA levels. High auxin accumulation in the tapetal cells and pollen grains promoted PsPK2 expression in those flower parts, and the interaction of auxin and PsPK2 overexpression reduced auxin response. |
