A subtracted cDNA library identifies genes up-regulated during PHOT1-mediated early step of de-etiolation in tomato (Solanum lycopersicum L.)

Petra Hloušková, Véronique Bergougnoux

De-etiolation is the switch from skoto- to photomorphogenesis, enabling the heterotrophic etiolated seedling to develop into an autotrophic plant. Upon exposure to blue light (BL), reduction of hypocotyl growth rate occurs in two phases: a rapid inhibition mediated by phototropin 1 (PHOT1) within the first 30-40 min of illumination, followed by the cryptochrome 1 (CRY1)-controlled establishment of the steady-state growth rate. Although some information is available for CRY1-mediated de-etiolation, less attention has been given to the PHOT1 phase of de-etiolation. We generated a subtracted cDNA library using the suppression subtractive hybridization method to investigate the molecular mechanisms of BL-induced de-etiolation in tomato (Solanum lycopersicum L.), an economically important crop. We focused our interest on the first 30 min following the exposure to BL when PHOT1 is required to induce the process. Our library generated 152 expressed sequence tags that were found to be rapidly accumulated upon exposure to BL and consequently potentially regulated by PHOT1. Annotation revealed that biological functions such as modification of chromatin structure, cell wall modification, and transcription/translation comprise an important part of events contributing to the establishment of photomorphogenesis in young tomato seedlings. Our conclusions based on bioinformatics data were supported by qRT-PCR analyses the specific investigation of V-H(+)-ATPase during de-etiolation in tomato. Our study provides the first report dealing with understanding the PHOT1-mediated phase of de-etiolation. Using subtractive cDNA library, we were able to identify important regulatory mechanisms. The profound induction of transcription/translation, as well as modification of chromatin structure, is relevant in regard to the fact that the entry into photomorphogenesis is based on a deep reprograming of the cell. Also, we postulated that BL restrains the cell expansion by the rapid modification of the cell wall.