The characterization of the soybean polygalacturonase-inhibiting proteins (Pgip) gene family reveals that a single member is responsible for the activity detected in soybean tissues

Polygalacturonase-inhibiting proteins (PGIPs) are leucine-rich repeat (LRR) proteins that inhibit fungal endopolygalacturonases (PGs). They are encoded by multigene families whose members show functional redundancy and subfunctionalization for recognition of fungal PGs. In order to expand the information on the structure and functional features of legume PGIP, we have isolated and characterized four members of the soybean Pgip gene family and determined the properties of the encoded protein products. Sequence analysis showed that these genes form two clusters: one cluster of about 5 kbp containing Gmpgip1 and Gmpgip2, and the other containing Gmpgip3 and Gmpgip4 within a 60 kb fragment of a separate BAC clone. Sequence diversification of the four members resides mainly in the xxLxLxx region that includes residues forming the β-sheet B1. When compared with other legume Pgip genes, Gmpgip3 groups with the bean genes Pvpgip1 and Pvpgip2, suggesting that these genes are closer to the ancestral gene. At the protein level, only GmPGIP3 shows the capability to inhibit fungal PGs. The spectrum of inhibition of GmPGIP3 against eight different fungal PGs mirrors that of the PGIP purified from soybean tissues and is similar to that of the bean PvPGIP2, one of the most efficient inhibitors so far characterized. We also report that the four Gmpgip genes are differentially regulated after wounding or during infection with the fungal pathogen Sclerotinia sclerotiorum. Following fungal infection Gmpgip3 is up regulated promptly, while Gmpgip2 is delayed.     

Developmental and age-related processes that influence the longevity and senescence of photosynthetic tissues in arabidopsis.

Factors that influence the longevity and senescence of photosynthetic tissues of Arabidopsis were investigated. To determine the influence of reproductive development on the timing of somatic tissue senescence, the longevity of rosette leaves of the Landsberg erecta strain and of isogenic mutant lines in which flowering is delayed (co-2) or sterile flowers are produced (ms1-1) were compared. No difference in the timing of senescence of individual leaves was observed between these lines, indicating that somatic tissue longevity is not governed by reproductive development in this species. To examine the role of differential gene expression in the process of leaf senescence, cDNA clones representing genes that are differentially expressed in senescing tissues were isolated. Sequence analysis of one such clone indicated homology to previously cloned cysteine proteinases, which is consistent with a role for the product of this gene in nitrogen salvage. RNA gel blot analysis revealed that increased expression of senescence-associated genes is preceded by declines in photosynthesis and in the expression of photosynthesis-associated genes. A model is presented in which it is postulated that leaf senescence is triggered by age-related declines in photosynthetic processes.