Polar auxin transport is required for the inhibition by blue light of the elongation-related LeEXT tomato gene

Hypocotyl elongation is an early developmental process regulated antagonistically by light and auxin. To highlight the interaction between both signals, we studied the photoregulation of the auxin-induced tomato (Lycopersicon esculentum Mill.) gene LeEXT involved in this process. RNA gel blot analysis indicated that this gene is down-regulated in response to blue light. We demonstrate that this response is principally mediated by the blue light photoreceptor cry1, but an interaction with the red/far-red light photoreceptors phyA, phyB1 and phyB2 has also been established. Furthermore, the polar auxin transport inhibitor NPA reverts the blue light inhibition of Lycopersicon esculentum gene encoding xyloglucan endotransglycosylase (LeEXT) expression, when it has the opposite effect in the dark or under red light. These results provide strong support for a specific interaction between auxin and blue light transduction pathways in the control of LeEXT expression, and therefore, of hypocotyl elongation in tomato.