P2SA1-induced Auxin Transport Regulates Arabidopsis Hypocotyl Phototropism

Plant, unlike animal, is immovabale and can’t give a quick and effective response to changeable environment. So, they evolved a unique mechanism to adapt to the change of external environment after hundreds of millions years evolution. Light as an important environmental factor, and profoundly affects plant growth and development process. To obtain moderate light and avoid high light damage, plants adapt their orientation toward light through the perception of lighting direction, light quality, light intensity and illumination time.Blue light receptor PHOT1 mediates Arabidopsis hypocotyl phototropism induced by low blue light and high blue light. PHOT2 regulates Arabidopsis hypocotyl phototropism induced by high blue light specifically. PHOT1 and PHOT2 display some kind of function redundant on Arabidopsis hypocotyl phototropism caused by high blue light, which limits the research on PHOT2 regulating Arabidopsis hypocotyls phototropism. To avoid interference of PHOT1, we chose phot1 mutant as EMS mutagenesis material and screened out P2SA1 as downstream signal regulator of PHOT2. The p2sa1 mutant lost hypocotyl phototropism in response to high blue light, but still had hypocotyl phototropism in response to low blue light. However, it is still unclear that the mechanism of P2SA1 regulating Arabidopsis hypocotyl phototropism induced by high blue light. Auxin asymmetrical distribution determines phototropism, thus we constructed p2sa1-DR5::GUS and p2sa1-DR5::GFP through hybridization between DR5::GUS、 DR5::GFP and p2sa1. With the treatment of unilateral high blue light, we found that auxin distributing changed from light side to backlight side in wild type after unilateral high blue light treatment, while auxin remained in cotyledon hook in p2sa1. The above results indicated that P2SA1 may regulate auxin lateral asymmetric distribution induced by high blue light, mediated hypocotyls phototropism. In order to further confirm P2SA1 regulation auxin transport, we detected auxin distribution in WT-DR5::GFP and p2sa1-DR5::GFP, the results were consistent with the GUS. P2SA1 regulated auxin asymmetric distribution in response to high blue light, and regulated Arabidopsis hypocotyl phototropism.Plants phototropism depends on auxin asymmetrical distribution, and auxin asymmetrical distribution depends on the effect of auxin transpoters. The expression level of PIN1, PIN2, PIN3, PIN4, PIN7, AUX1, ABCB19, GNOM, ABP1, ARF19, AXR1, IAA19 and TIR1 which are related to auxin’s transportation, perception, and signal transfer were tested. We found that high blue light treatment significantly induced PIN1, PIN7 and ABP1 gene expression both in wild type and p2sa1 mutant, whereas other genes had not been induced under high blue light treatment. The results showed that the induced expression of PIN1, PIN7, ABP1 under high blue light may not be affected by P2SA1. Then, we tested the GUS and GFP changes of PIN2、PIN3、PIN4 and PIN7 induced by high blue light under Arabidopsis wild-type and p2sa1 mutant background. The results showed that they existed in the cotyledon, cotyledon and hypocotyl, cotyledon and vascular tissue,cotyledon and hypocotyl respectively. The results of GFP distribution were consistent with the results of GUS distribution under wild type and mutant background, which auxin distribution didn’t change.In addition, we discussed the effect of the mutation of blue light receptors phototropins and cryptochromes on the blue light corresponding gene expression. PHOT signaling pathways involved in regulating ABP1 expression. CRY signaling pathways may regulate ABP1 gene expression bymass. CRY and PHOT may participate in regulating the ABP1 gene, prompting auxin asymmetrical distribution differences between WT and p2sa1. As a result, p2sa1 didn’t response to unilateral high blue light caused hypocotyls phototropism.In conclusion, we screened P2SA1 genes, which involved in regulating Arabidopsis hypocotyls phototropism induced by high blue light. P2SA1 regulated the lateral asymmetry distribution of auxin. PIN1, PIN7, ABP1 performed significant expression levels in response to high blue light. Auxin transporters PIN2, PIN3, PIN4 and PIN7 might not induce auxin lateral asymmetry distribution in response to high blue light. CRY and PHOT may participate in regulating ABP1 together, prompt auxin different distribution and cause hypocotyl phototropism.