The expression of LESK1 morphogenetic marker along the tomato hypocotyl axis is linked to a position-dependent competence for shoot regeneration

Somatic morphogenesis is an important process whose mechanisms are still not completely understood. This is partially due to the lack of reliable morphogenetic markers that identify the different stages of the process. In the present work, a fragment of LESK1 gene (Lycopersicon esculentum shoot kinase 1) has been utilized as a marker of somatic caulogenesis. The expression of this marker pointed out a particular abundance of the corresponding transcript in tomato hypocotyls from 8-day-old plantlets. This elevated expression underlines the particular attitude to regeneration of this organ. Hypocotyl explants can in fact regenerate in the absence of exogenous growth regulators giving rise to shoot and root production at the apical and basal ends, respectively. The polarization observed in morphogenesis is always associated with polarized expression of LESKI gene, which is elevated at the top of the explants. where shoot production occurs, and low at the basal pole, where roots were observed. A non-homogeneous LESKI expression was also found along the hypocotyl axis where apparently marks cell populations with different competence to caulogenesis. These different levels of competence may be due to a variation in cell sensitivity to growth regulators, or the reaching of a well determined hormonal ratio required by the cells to be driven toward caulogenesis. LESK1 represents a reliable marker probably linked to the acquisition of competence for somatic caulogenesis.