Selective lignin downregulation leads to constitutive defense response expression in alfalfa (Medicago sativa L.).
• Downregulation of hydroxycinnamoyl CoA: shikimate hydroxycinnamoyl transferase (HCT) in alfalfa (Medicago sativa) reduces lignin levels and improves forage quality and saccharification efficiency for bioethanol production. However, the plants have reduced stature. It was previously reported that HCT-down-regulated Arabidopsis have impaired auxin transport, but this has recently been disproved. • To address the basis for the phenotypes of lignin-modified alfalfa, we measured auxin transport, profiled a range of metabolites including flavonoids and hormones, and performed in depth transcriptome analyses. • Auxin transport is unaffected in HCT antisense alfalfa despite increased flavonoid biosynthesis. The plants show increased cytokinin and reduced auxin levels, and gibberellin levels and sensitivity are both reduced. Levels of salicylic, jasmonic and abscisic acids are elevated, associated with massive upregulation of pathogenesis and abiotic stress-related genes and enhanced tolerance to fungal infection and drought. • We suggest that HCT downregulated alfalfa plants exhibit constitutive activation of defense responses, triggered by release of bioactive cell wall fragments and production of hydrogen peroxide as a result of impaired secondary cell wall integrity.
Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA.
Lina
L
Gallego-Giraldo
Yusuke
Y
Jikumaru
Yuji
Y
Kamiya
Yuhong
Y
Tang
Richard A
RA
Dixon
D015100:3,3'-Diaminobenzidine / Q000378:metabolism; D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism; D000222:Adaptation, Physiological / Q000187:drug effects; D001692:Biological Transport / Q000187:drug effects; D020231:Colletotrichum / Q000187:drug effects / Q000502:physiology; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005875:Gibberellins / Q000494:pharmacology; D007210:Indoleacetic Acids / Q000378:metabolism; D008031:Lignin / Q000235:genetics*; D000455:Medicago sativa / Q000201:enzymology / Q000235:genetics* / Q000276:immunology* / Q000382:microbiology; D008954:Models, Biological; D010636:Phenols / Q000378:metabolism; D010641:Phenotype; D018515:Plant Leaves / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018547:Plant Stems / Q000187:drug effects / Q000254:growth & development; D016372:RNA, Antisense / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013312:Stress, Physiological / Q000187:drug effects; D014230:Triazoles / Q000494:pharmacology
D005875:Gibberellins; D007210:Indoleacetic Acids; D010636:Phenols; D010940:Plant Proteins; D016372:RNA, Antisense; D012333:RNA, Messenger; D014230:Triazoles; D015100:3,3'-Diaminobenzidine; C053370:paclobutrazol; D008031:Lignin; D000217:Acyltransferases