Tomato mitogen activated protein kinases regulate the expression of extracellular invertase Lin6in response to stress related stimuli.

Activation of mitogen-activated protein kinases (MAPKs) is a common reaction of plant cells in defence-related signal transduction pathways. Since the downstream events after the activation of MAPKs are largely unknown in plants, the role of MAPKs in the coordinate regulation of defence reactions and primary carbon metabolism by stress related stimuli has been analysed in tomato (Lycopersicon peruvianumMill.). Thus, the relationship between MAPK, LpMPK2 and LpMPK3 and extracellular invertase Lin6, as the key enzyme of an apoplasmic phloem unloading pathway, has been analysed. It was observed that the mRNAs of LpMPK3and Lin6are sequentially induced by the same set of stress related stimuli, wounding, a fungal elicitor derived from Fusarium oxysporum lycopersici, the endogenous plant derived elicitor PGA and salt stress, while LpMPK2transcripts are constitutively expressed. In a gain of function approach, a His-tagged version of LpMPK2and a HA-tagged version of LpMPK3were transiently and functionally expressed in leaves of transgenic tobacco (Nicotiana tabacumL.) plants expressing the β-glucuronidase reporter gene under control of the Lin6promoter via agro-infection. The induction of the Lin6promoter, as revealed by an increase in β-glucuronidase activity after 24h, was dependent both on the expression and activation of both LpMPK2 and LpMPK3. These data suggest that the induction of extracellular invertase Lin6 by stress-related stimuli requires LpMPK2 and LpMPK3, and thus demonstrate that MAPK signalling might be involved in the regulation of primary carbon metabolism in general and sink metabolism in particular. [ABSTRACT FROM AUTHOR]