In this work, we study the function of the Medicago truncatula ST4, ST5 and ST6 proteins that belong to a protein
family of unknown function characterized by the DUF2775 domain. Thus, we analyse their promoter sequence
and activity, their transcript accumulation, and their subcellular location. The analysis of the three promoters
showed different combination of cis-acting regulatory elements and they presented different activity pattern.
Throughout development only ST6 mRNAs have been detected in most of the stages analysed, while ST4 was
faintly detected in the roots and in the flowers and ST5 was always absent. The addition of MeJA, ET and SA
revealed specific responses of the STs, the ST4 transcript accumulation increased by MeJA; the ST5 by MeJA and
ET when applied together; and the ST6 by ET and by SA. Finally, the ST4 and ST5 proteins were in the cell wall
whereas the ST6 had a dual location. From these results, we can conclude that the ST4, ST5 and ST6 RNAs are
specifically and differentially up-regulated by MeJA, ET and SA, plant regulators also involved in the plant
defence, pointing that ST4, ST5 and ST6 proteins might be involved in specific biotic interactions through
different signalling pathways.
