Is the synthesis of strigolactones and ABA co-ordinately repressed under irrigated conditions? A case study on ORA47 in Arabidopsis and tomato

The ORA47 (Octadecanoid-Responsive AP2/ERF-domain transcription factor 47) transcription factor of Arabidopsis has been found to bind the promoter regions of ABA and strigolactone biosynthetic genes during normal, but not drought conditions. Since the transcription of those same genes is activated in leaves under drought, the possibility was raised that ORA47 acts as a repressor of strigolactone and ABA synthesis, to be removed under drought for the levels of these hormones to rise. Thus, being interested in the strigolactone-ABA cross-talk with respect to the plant water status, we set to elucidate the role of this transcription factor by contrasting plants with altered ORA47 expression and their respective control genotypes. Specifically, tomato ora47 TILLING lines in a M82 background with constitutively knocked ORA47 expression; and Arabidopsis lines overexpressing ORA47 under the control of an inducible promoter were obtained. Their molecular and physiological characterisation is still in progress; yet, preliminary results in tomato showed that the ora47 knockout line has lower stomata conductance under irrigated conditions, and possibly lower sensitivity to water deprivation than sister-line controls. The expression of the SlNCED4 gene, biosynthetic of ABA, was indeed increased under irrigated conditions. Also, the stem of the ora47 knock-out line has the same functional hydraulic conductivity of its corresponding sister line, while the conductive xylem area is significantly lower. All of these observations are consistent with the initial hypothesis, though in need of further confirmation.