title: Hormone-regulated defense and stress response networks contribute to heterosis in Arabidopsis F1 hybrids.
abstract: Plant hybrids are extensively used in agriculture to deliver increases in yields, yet the molecular basis of their superior performance (heterosis) is not well understood. Our transcriptome analysis of a number of Arabidopsis F1 hybrids identified changes to defense and stress response gene expression consistent with a reduction in basal defense levels. Given the reported antagonism between plant immunity and growth, we suggest that these altered patterns of expression contribute to the greater growth of the hybrids. The altered patterns of expression in the hybrids indicate decreases to the salicylic acid (SA) biosynthesis pathway and increases in the auxin [indole-3-acetic acid (IAA)] biosynthesis pathway. SA and IAA are hormones known to control stress and defense responses as well as plant growth. We found that IAA-targeted gene activity is frequently increased in hybrids, correlating with a common heterotic phenotype of greater leaf cell numbers. Reduced SA concentration and target gene responses occur in the larger hybrids and promote increased leaf cell size. We demonstrated the importance of SA action to the hybrid phenotype by manipulating endogenous SA concentrations. Increasing SA diminished heterosis in SA-reduced hybrids, whereas decreasing SA promoted growth in some hybrids and phenocopied aspects of hybrid vigor in parental lines. Pseudomonas syringae infection of hybrids demonstrated that the reductions in basal defense gene activity in these hybrids does not necessarily compromise their ability to mount a defense response comparable to the parents.
authors.affiliation: CSIRO Agriculture, Canberra, ACT 2601, Australia;
authors.forename: Michael
authors.initials: M
authors.lastname: Groszmann
authors.affiliation: CSIRO Agriculture, Canberra, ACT 2601, Australia;
authors.forename: Rebeca
authors.initials: R
authors.lastname: Gonzalez-Bayon
authors.affiliation: CSIRO Agriculture, Queensland Bioscience Precinct, Brisbane, QLD 4069, Australia;
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Lyons
authors.affiliation: CSIRO Agriculture, Canberra, ACT 2601, Australia;
authors.forename: Ian K
authors.initials: IK
authors.lastname: Greaves
authors.affiliation: CSIRO Agriculture, Queensland Bioscience Precinct, Brisbane, QLD 4069, Australia;
authors.forename: Kemal
authors.initials: K
authors.lastname: Kazan
authors.affiliation: CSIRO Agriculture, Canberra, ACT 2601, Australia; University of Technology, Sydney, NSW 2007, Australia jim.peacock@csiro.au.
authors.forename: W James
authors.initials: WJ
authors.lastname: Peacock
authors.affiliation: CSIRO Agriculture, Canberra, ACT 2601, Australia; University of Technology, Sydney, NSW 2007, Australia.
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Dennis
mesh_terms: D017360:Arabidopsis / Q000378:metabolism* / Q000382:microbiology; D002678:Chimera / Q000378:metabolism* / Q000382:microbiology; D060467:Disease Resistance / Q000502:physiology; D006823:Hybrid Vigor / Q000502:physiology*; D007210:Indoleacetic Acids / Q000378:metabolism; D010935:Plant Diseases / Q000382:microbiology; D010937:Plant Growth Regulators / Q000378:metabolism*; D044224:Pseudomonas syringae / Q000378:metabolism; D020156:Salicylic Acid / Q000378:metabolism; D013312:Stress, Physiological / Q000502:physiology*
chemical_list: D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D020156:Salicylic Acid
keywords: auxin; biomass; hybrid vigor; plant defense; salicylic acid