The delay in hormonal treatment modulates the expression of LESK1,a gene encoding a putative serine-threonine kinase, marker of in vitro caulogenesis in tomato (Lycopersicon esculentum Mill.)

Growth regulators play a multiple role in somatic organogenesis, affecting the phases of competence acquisition, determination and organ differentiation. The establishment of these phases is conceivably determined by a differential gene expression. We have recently found that the expression of LESK1, a gene that encodes a putative serine/threonine kinase marks an elevated intrinsic caulogenetic attitude in tomato hypocotyl, that does not require the presence of exogenous growth regulators. In tomato cotyledon explants, caulogenesis is instead induced supplying the culture medium with growth regulators. In these explants, LESK1 expression peak precedes the induction phase and marks the acquisition of caulogenic competence. The removal of growth regulators just after the reaching of the peak prevents the achievement of an optimal shoot production. A delay in hormonal treatment greatly reduced caulogenesis, affecting both competence acquisition, as suggested by the reduced LESK1 expression, and consequently the proper induction, driving to a sharp decrease in shoot primordia per explant. We hypothesize that LESK1 kinase is activated during the transduction of the hormonal signal driving to caulogenesis and required for the fulfillment of the inductive phase. LESK1 expression is differently modulated in tomato horticultural varieties showing different caulogenic attitude. As all the examined cultivars have one copy of this gene, a different regulation of the hormonal signal transduction pathway involving LESK1, is conceivably responsible for the diverse morphogenetic outcomes in these varieties.