The accumulation of a Kunitz trypsin inhibitor from chickpea (TPI‐2) located in cell walls is increased in wounded leaves and elongating epicotyls

Abstract

Here, we report the identification and characterization of CaTPI-2, which is a member of a Cicer arietinum gene family encoding Kunitz-type proteinase inhibitors with at least two members -CaTPI-1 and CaTPI-2. The widespread mRNA accumulation of CaTPI-2 in all the different organs of 4-day-old etiolated seedlings and in stem internodes differs from the more specific Cicer arietinum Trypsin Proteinase Inhibitor-1 (CaTPI-1) transcription. After the generation of polyclonal antibodies against the recombinant Trypsin Proteinase Inhibitor-2 (TPI-2) protein, the protein was located in the cell walls of vegetative organs. The decrease found in both transcription and TPI-2 protein levels when the epicotyls aged, together with the wider and more intensive immunostaining of the protein in apical zones of epicotyls and radicles, in consonance with their higher elongation rate, indicated a relationship of the TPI-2 protein with the elongation process. CaTPI-2 mRNA levels were increased by wounding in both epicotyls and leaves. The accumulation of CaTPI-2 mRNA in seedlings, which was further amplified by mechanical wounding in epicotyls and leaves, suggests the involvement of TPI-2 in the response to wounds. Our results indicate that TPI-2 protein has features different from those of the former characterized Trypsin Proteinase Inhibitor-1 (TPI-1), such as its different gene regulation under light, a different cellular location and its upregulation by wounding, which implies a function different from that of TPI-1 in chickpea metabolism.