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Polygalacturonase-inhibiting proteins (PGIPs) are leucine-rich repeat (LRR) proteins that inhibit polygalacturonase (PG) enzymes secreted by pathogens to break down plant cell walls during early stage of disease development. Sugar beet ( Beta vulgaris L.) PGIP genes ( BvPGIPs ) have 11 LRR domains as compared to 10 LRRs generally found in other plant species. To determine whether the BvPGIPs have a function in plant defense, genes encoding BvPGIP1 and BvPGIP2 that differ in 8 amino acids were fused with the CaMV 35S constitutive promoter and introduced into Nicotiana benthamiana . Crude PGIP protein extracts from BvPGIP1 transgenic plants significantly inhibited Rhizoctonia solani , Fusarium solani and Botrytis cinerea PGs. BvPGIP2 extract also inhibited PGs from F. solani and B. cinerea but did not inhibit PGs from R . solani . When transgenic BvPGIP plants were bioassayed for resistance, similar results were obtained. This is a first report that documents sugar beet PGIPs with 11 LRRs confer resistance to three different fungal pathogens. [ABSTRACT FROM AUTHOR]

Polygalacturonase-inhibiting proteins (PGIPs) are leucine-rich repeat (LRR) proteins involved in plant defense. Three sugar beet ( Beta vulgaris L.) PGIP genes, BvPGIP1 , BvPGIP2 and BvPGIP3 , were isolated from breeding line F1016 and BvPGIP2 and BvPGIP3 from F1010. Full-length cDNA sequences of the three BvPGIP genes encoded a 382 or 384 amino acid peptide. They shared closest similarity with five PGIP -like sequences found in the sugar beet reference genome (RefBeet 1.2.1) as well as Bv ( FC607 ) PGIP1 and Bv ( FC607 ) PGIP2 from sugar beet breeding line FC607. The predicted structure of BvPGIP1, 2 and 3 peptides was that of Phaseolus vulgaris PvPGIP2 with the exception that the sugar beet peptides were about 40 amino acids longer and encoded an additional LRR repeat. RT-PCR and qPCR analyses demonstrated BvPGIP gene expression in leaves, petioles, hypocotyls and highest expression in roots. Leaf and root BvPGIP transcripts increased in response to insect feeding and mechanical wounding. An agarose radial diffusion assay showed that BvPGIP protein extracts inhibited polygalacturonases (PGs) of Rhizoctonia solani , Fusarium oxysporum f. sp. gladioli and F. oxysporum f. sp. betae with the exception that PGIP extracts from line F1010 did not inhibit R. solani PGs. These findings identify sugar beet PGIP genes that encode LRR domains that are longer than reported for most other species. In addition, the wound up-regulated BvPGIP gene expression and inhibition of fungal PGs by PGIP extracts suggest that like other plant PGIPs, the sugar beet genes may play an active role in defense responses. [ABSTRACT FROM AUTHOR]