A LTR copia retrotransposon and Mutator transposons interrupt Pgip genes in cultivated and wild wheats

Cucumber PGIP2 is involved in resistance to gray mold disease

Polygalacturonase inhibitor protein (PGIP) restricts fungal growth and colonization and functions in plant immunity. Gray mold in cucumber is a common fungal disease caused by Botrytis cinerea, and is widespread and difficult to control in cucumber (Cucumis sativus L.) production. In this study, Cucumis sativus polygalacturonase-inhibiting protein 2 (CsPGIP2) was found to be upregulated in response to gray mold in cucumber. CsPGIP2 was detected in the endoplasmic reticulum, cell membrane, and cell wall after transient transformation of protoplasts and tobacco. A possible interaction between Botrytis cinerea polygalacturonase 3 (BcPG3) and CsPGIP2 was supported by protein interaction prediction and BiFC analysis. Transgenic Arabidopsis plants expressing CsPGIP2 were constructed and exhibited smaller areas of gray mold infection compared to wild type (WT) plants after simultaneous inoculation. Evans blue dye (EBD) confirmed greater damage for WT plants, with more intense dyeing than for the transgenic Arabidopsis. Interestingly, compared to WT, transgenic Arabidopsis exhibited higher superoxide dismutase (AtSOD1) expression, antioxidant enzyme activities, lignin content, net photosynthetic rate (Pn), and photochemical activity. Our results suggest that CsPGIP2 stimulates a variety of plant defense mechanisms to enhance transgenic Arabidopsis resistance against gray mold disease.

Unraveling the genomic reorganization of polygalacturonase-inhibiting proteins in chickpea

Polygalacturonase-inhibiting proteins (PGIPs) are cell wall proteins that inhibit pathogen polygalacturonases (PGs). PGIPs, like other defense-related proteins, contain extracellular leucine-rich repeats (eLRRs), which are required for pathogen PG recognition. The importance of these PGIPs in plant defense has been well documented. This study focuses on chickpea (Cicer arietinum) PGIPs (CaPGIPs) owing to the limited information available on this important crop. This study identified two novel CaPGIPs (CaPGIP3 and CaPGIP4) and computationally characterized all four CaPGIPs in the gene family, including the previously reported CaPGIP1 and CaPGIP2. The findings suggest that CaPGIP1, CaPGIP3, and CaPGIP4 proteins possess N-terminal signal peptides, ten LRRs, theoretical molecular mass, and isoelectric points comparable to other legume PGIPs. Phylogenetic analysis and multiple sequence alignment revealed that the CaPGIP1, CaPGIP3, and CaPGIP4 amino acid sequences are similar to the other PGIPs reported in legumes. In addition, several cis-acting elements that are typical of pathogen response, tissue-specific activity, hormone response, and abiotic stress-related are present in the promoters of CaPGIP1, CaPGIP3, and CaPGIP4 genes. Localization experiments showed that CaPGIP1, CaPGIP3, and CaPGIP4 are located in the cell wall or membrane. Transcript levels of CaPGIP1, CaPGIP3, and CaPGIP4 genes analyzed at untreated conditions show varied expression patterns analogous to other defense-related gene families. Interestingly, CaPGIP2 lacked a signal peptide, more than half of the LRRs, and other characteristics of a typical PGIP and subcellular localization indicated it is not located in the cell wall or membrane. The study's findings demonstrate CaPGIP1, CaPGIP3, and CaPGIP4's similarity to other legume PGIPs and suggest they might possess the potential to combat chickpea pathogens.

Molecular characterization of five novel Wx-A1 alleles in common wheat including one silent allele by transposon insertion

Wheat starch is composed of two glucose polymers, amylose and amylopectin. Although several starch synthases are responsible for its synthesis, only the waxy protein is associated with the amylose synthesis. The waxy protein composition of 45 Spanish common wheat landraces from Andalusia (southern Spain) was evaluated. Within these materials, five novel alleles for the Wx-A1 gene were detected. Four of them showed functional proteins (Wx-A1p, Wx-A1q, Wx-A1r and Wx-A1s), although some amino acid changes were found in the mature protein sequence. However, one of them (Wx-A1t) exhibited loss of the Wx-A1 protein, and its base sequence contained one large insert (1,073 bp) in the tenth exon, that interrupted the ORF of the Wx-A1 gene. This insert exhibited the characteristics of a Class II transposon of the Mutator superfamily, which had not been described previously, and has been named Baetica. The conservation of such inserts could be related to their low effect on vital properties of the plants, as occurs with most of the genes associated with technological quality. In conclusion, the evaluation of old wheat landraces showed that, in addition to their use as alternative crops, these materials could be a useful source of interesting genes in wheat quality improvement.

An update on polygalacturonase-inhibiting protein (PGIP), a leucine-rich repeat protein that protects crop plants against pathogens

Polygalacturonase inhibiting proteins (PGIPs) are cell wall proteins that inhibit the pectin-depolymerizing activity of polygalacturonases secreted by microbial pathogens and insects. These ubiquitous inhibitors have a leucine-rich repeat structure that is strongly conserved in monocot and dicot plants. Previous reviews have summarized the importance of PGIP in plant defense and the structural basis of PG-PGIP interaction; here we update the current knowledge about PGIPs with the recent findings on the composition and evolution of pgip gene families, with a special emphasis on legume and cereal crops. We also update the information about the inhibition properties of single pgip gene products against microbial PGs and the results, including field tests, showing the capacity of PGIP to protect crop plants against fungal, oomycetes and bacterial pathogens.

Functional characterisation of wheat Pgip genes reveals their involvement in the local response to wounding

Polygalacturonase-inhibiting proteins (PGIPs) are cell wall leucine-rich repeat (LRR) proteins involved in plant defence. The hexaploid wheat (Triticum aestivum, genome AABBDD) genome contains one Pgip gene per genome. Tapgip1 (B genome) and Tapgip2 (D genome) are expressed in all tissues, whereas Tapgip3 (A genome) is inactive because of a long terminal repeat, Copia retrotransposon insertion within the coding region. To verify whether Tapgip1 and Tapgip2 encode active PGIPs and are involved in the wheat defence response, we expressed them transiently and analysed their expression under stress conditions. Neither TaPGIP1 nor TaPGIP2 showed inhibition activity in vitro against fungal polygalacturonases. Moreover, a wheat genotype (T. turgidum ssp. dicoccoides) lacking active homologues of Tapgip1 or Tapgip2 possesses PGIP activity. At transcript level, Tapgip1 and Tapgip2 were both up-regulated after fungal infection and strongly induced following wounding. This latter result has been confirmed in transgenic wheat plants expressing the β-glucuronidase (GUS) gene under control of the 5'-flanking region of Tdpgip1, a homologue of Tapgip1 with an identical sequence. Strong and transient GUS staining was mainly restricted to the damaged tissues and was not observed in adjacent tissues. Taken together, these results suggest that Tapgips and their homologues are involved in the wheat defence response by acting at the site of the lesion caused by pathogen infection.

Molecular characterization of the Sasanda LTR copia retrotransposon family uncovers their recent amplification in Triticum aestivum (L.) genome

Retrotransposons constitute a major proportion of the Triticeae genomes. Genome-scale studies have revealed their role in evolution affecting both genome structure and function and their potential for the development of novel markers. In this study, family members of an LTR copia retrotransposon which mediated the duplication of the gene encoding the high molecular weight glutenin subunit Bx7 in cultivar Glenlea were characterized. This novel element was named Sasanda_EU157184-1 (TREP3516). High density filters of the Glenlea hexaploid wheat BAC library were screened with a Sasanda long terminal repeat (LTR)-specific probe and approximately 1,075 positive clones representing an estimated copy number of 347 elements per haploid genome were identified. The 242 BAC clones with the strongest hybridization signal were selected. To maximize isolation of complete elements, this subset of clones was screened with a reverse transcriptase (RT) domain probe and DNA was isolated from the 133 clones that produced a strong hybridization signal. Left (5') and right (3') LTRs as well as the RT domains were PCR amplified and sequencing was carried out on the final subset of 121 clones. Evolutionary relationships were inferred from a data set consisting of 100 RT, 102 5' LTR and 100 3' LTR sequences representing 233, 451 and 495 informative sites for comparison, respectively. Neighbour-joining tree indicated that the element is at least 1.8 million years old and has evolved into a minimum of five sub-families. The insertion times of the 89 complete elements were estimated based on the divergence between their LTRs. Corroborating the inference from the RT domain, analysis of the LTR domains also indicated bursts of amplification from 2.6 million years ago (MYA) to now, except for one member dated to 4.6 +/- 0.7 MYA, which corresponds to the interval of divergence of Triticum and Aegilops (3 MYA) and divergence of Triticum and Rye (7 MYA). In 44 elements, the 5' and 3' LTRs were identical indicating recent transposition activity. The element can be used to develop retrotransposon-based markers such as sequence-specific amplified polymorphism, retrotransposon microsatellite amplified polymorphism and inter-retrotransposon amplified polymorphism, all of which are well suited for genotyping studies.