DIFFERENTIAL RNA TRANSCRIPT ACCUMULATION OF pgip MEMBERS
DURING NORMAL GROWTH AND DEVELOPMENT IN Phaseolus vulgaris L:.
Serena Roberti, Federica Marini and Renato D’Ovidio
Dipartimento di Agrobiologia e Agrochimica, Università degli studi della Tuscia, Via San Camillo
de Lellis, s.n.c., 011100 Viterbo, Italy. Email: dovidio@unitus.it
Polygalacturonase-inhibiting proteins (PGIPs) are plant cell wall glycoproteins that inhibit
fungal endopolygalacturonases (PG) and modulate their activity favoring the
accumulation of oligogalacturonides active as elicitors of plant defense responses.
Biochemical and RNA analysis indicate that the expression of bulk PGIP and of the their
encoding genes, as a whole, undergoes tissue-specific accumulation and induction
following environmental stresses. Recently, the genomic organization of the bean pgip
family has been determined, and have been shown to be represented by four different
members (Pvpgip1, Pvpgip2, Pvpgip3 and Pvpgip4) showing 79-97% similarity at nucleotide
level. Nucleotide sequence information were used to develop primer pairs specific for
each member. RT-PCR assays were performed to identify the specific regulation of each
member and their contribution to the final transcript level during the normal growth and
development of bean plants. Expression of PGIP genes was analyzed in various tissues
and organs including stems, roots and pods. The analysis was performed both in etiolated
and light-grown plants. RNA transcripts corresponding to all four genes were detected in
all tissue analyzed, with Pvpgip2 being the most represented. Pvpgip1 was weakly present
in all tissues, whereas Pvpgip3 and Pvpgip4 transcripts were abundant in the hypocotyls
and weakly represented in the roots. Real-time PCR analysis of Pvpgip2 transcript indicate
also a seven-fold difference between etiolated and light grown tissues. The constant
presence of Pvpgip2 transcript in all tissues analyzed is in agreement with its recognition
capabilities against fungal polygalacturonases. In fact, PvPGIP2 is the most effective
inhibitors between the four bean PGIPs. The distribution of Pvpgip3 and Pvpgip4 mainly
in the epigeous part could be related to their effectiveness against pathogens specific for
these tissues or to their involvement in additional physiological aspects related to the
differentiation of light-grown tissue.