Publication: Fructan and glucan-mediated immunity to combat drought stress in Musa spp
Abstract
Fruktanlar ve glukanlar, bitkilerde doğal olarak bulunan polisakkaritlerdir ve belirli mikroorganizmalar tarafından sentezlenebilirler. Genel olarak, bitki fruktanları ana depolama karbohidratları olarak bilinir ve immünomodülatörler olarak çalışılmıştır. Bununla birlikte, bitkilerde fruktan oluşumu da abiyotik stres direncine bağlanmıştır. Potansiyel olarak, fruktanlar ve fruktooligosakkaritler bağışıklık sistemini indükleyebilir ve hatta çeşitli metabolitlerin gen ekspresyon profillerini sinyal transdüksiyon kaskadları aracılığıyla modüle edebilir ve böylece bitki savunma mekanizmasını hazırlayarak geliştirebilirler.Dünyanın en önemli temel besin maddelerinden olan muz (Musa spp.), doğal fruktan akümülatörü olarak bilinir ve kuraklığa karşı oldukça savunmasızdır. Kuraklığa karşı dayanıklı ve dayanıksız muz çeşitleri arasında yapılan genom düzeyindeki çalışmalar sayesinde karbonhidrat metabolizmasının regülasyonunda ve stres tolerans mekanizmalarında şekerlerin rolünü öne süren önemli farklılığa dikkat çekilmiştir.Bitki savunmasında glukanların ve fruktanların fonksiyonel rollerini araştırmak için, farklı polimerizasyona sahip mikrobiyal ve bitki kökenli fruktanlar ile yulaf türevi β-glukanlar 3 aylık muz bitkileri üzerinde yaprak yüzeyine püskürtme ve puro yaprak yoluyla bitki gövdesine enjekte etme ile test edilmiştir. Sera koşullarında, 5 hafta boyunca kuraklık stresine maruz bırakılan bitkilerin yaprak doku örnekleri, toprak pF değeri 2.8'e eşit veya daha yüksek olduğunda toplanmaya başlanmıştır. Puro yaprak yoluyla fruktan ve glukan ile test edilen bitkilerde yapılan yaprak yüzey alanı ölçümlerinde daha düzgün bir büyüme profile ile daha düşük kuraklık stresi seviyelerine rastlanmıştır. Şeker bağışıklığı kavramı, şeker metabolisması ve bu metabolizmada görev alan farklı invetaz enzimlerinin aktivilerinin tayini ile ekinlerde kuraklık toleransında rol oynadığı bilinen MYB ve YABBY genlerinin ekspresyon düzeylerinin incelenmesi yoluyla araştırılmıştır. Bu tez çalışmasında incelenen genler arasında, MYB94 geni farklı fruktan yapılarının muzlarda kuraklık ile mücadelede olası rolüne ışık tutmuştur. Şeker metabolismasının ve stress ile ilişki gen ekspresyonu modellerinin incelenmesi ve bu alanda yapılacak daha fazla çalışma ile bağışıklık düzenleyici olarak bilinen fruktan ve glukanların kuraklık ile mücadeledeki fonksiyonel rolleri hakkında daha iyi bir bakış sunması beklenmektedir.
Fructans and glucans are naturally-occurring polysaccharides in plants and can be synthesized by certain microorganisms. Generally, plant fructans are known as the main storage carbohydrates and have been studied as immunomodulators. However, their occurrence has also been linked to abiotic stress resistance. Potentially, fructans and fructooligosaccharides can induce immune responses and even enhance them by modulating gene expression profiles of various metabolites via signal transduction cascades thus priming plant defense mechanism. Bananas (Musa spp.), one of the most important staple foods in the world, are natural fructan accumulators and highly vulnerable to drought. Genome level studies highlighted the significant difference in the regulation of carbohydrate metabolism between drought-resistant and non-resistant banana varieties suggesting the role of sugars in stress tolerance mechanisms.To explore the functional roles of glucans and fructans in plant defense, several plant and microbial-derived fructans of a different degree of polymerization and oat-derived β-glucans were tested by leaf and cigar priming on 3-month-old banana plants subjected to 5 weeks of water deprivation under greenhouse conditions. Leaf tissues were collected when the soil pF value was equal or higher than 2.8. Based on leaf area, cigar-primed plants showed lower stress levels with more uniform growth profile. Sugar immunity concept was also explored by studying expression levels of MYB and YABBY genes which were known to play role in drought tolerance in crops. Among the genes studied in this thesis, the most interesting data was obtained from MYB94 sugesting a possible role for several fructans to combat drought stress in banana. Further research on quantification of internal sugar levels, other stress-related gene expression patterns and enzymatic activities involved in sugar metabolism are expected to provide a good overview of banana stress responses under drought and the functional roles of fructans and glucans as immune response modifiers.
Fructans and glucans are naturally-occurring polysaccharides in plants and can be synthesized by certain microorganisms. Generally, plant fructans are known as the main storage carbohydrates and have been studied as immunomodulators. However, their occurrence has also been linked to abiotic stress resistance. Potentially, fructans and fructooligosaccharides can induce immune responses and even enhance them by modulating gene expression profiles of various metabolites via signal transduction cascades thus priming plant defense mechanism. Bananas (Musa spp.), one of the most important staple foods in the world, are natural fructan accumulators and highly vulnerable to drought. Genome level studies highlighted the significant difference in the regulation of carbohydrate metabolism between drought-resistant and non-resistant banana varieties suggesting the role of sugars in stress tolerance mechanisms.To explore the functional roles of glucans and fructans in plant defense, several plant and microbial-derived fructans of a different degree of polymerization and oat-derived β-glucans were tested by leaf and cigar priming on 3-month-old banana plants subjected to 5 weeks of water deprivation under greenhouse conditions. Leaf tissues were collected when the soil pF value was equal or higher than 2.8. Based on leaf area, cigar-primed plants showed lower stress levels with more uniform growth profile. Sugar immunity concept was also explored by studying expression levels of MYB and YABBY genes which were known to play role in drought tolerance in crops. Among the genes studied in this thesis, the most interesting data was obtained from MYB94 sugesting a possible role for several fructans to combat drought stress in banana. Further research on quantification of internal sugar levels, other stress-related gene expression patterns and enzymatic activities involved in sugar metabolism are expected to provide a good overview of banana stress responses under drought and the functional roles of fructans and glucans as immune response modifiers.