Abscisic acid negatively regulates post-penetration resistance of Arabidopsis to the biotrophic powdery mildew fungus

Pytohormone abscisic acid （ABA） plays important roles in defense responses. Nonetheless, how ABA regulates plant resistance to biotrophic fungi remains largely unknown. Arabidopsis ABA-deficient mutants, aba2-1 and aba3-1, displayed enhanced resistance to the biotrophic powdery mildew fungus Golovinomyces cichoracearum. Moreover, exogenously administered ABA increased the susceptibility of Arabidopsis to G. cichoracearum. Arabidopsis ABA perception components mutants, abil-1 and abi2-1, also displayed similar phenotypes to ABA-deficient mutants in resistance to G. cichoracearum. However, the resistance to G. cichoracearum is not changed in downstream ABA signaling transduction mutants, abi3-1, abi4-1, and abi5-1. Microscopic examination revealed that hyphal growth and conidiophore production of G. cichoracearum were compromised in the ABA deficient mutants, even though pre-penetration and penetration growth of the fimgus were not affected. In addition, salicylic acid （SA） and MPK3 are found to be involved in ABA-regulated resistance to G. cichoracearurn. Our work demonstrates that ABA negatively regulates post-penetration resistance of Arabidopsis to powdery mildew fungus G. cichoracearum, probably through antagonizing the function of SA.

New insights in the battle between wheat and Puccinia striiformis

Wheat stripe rust caused by Puccinia striiformis f.sp.tritici(Pst)poses a great threat to wheat production worldwide.The rapid change in virulence of Pst leads to a loss of resistance in currently resistant wheat cultivars,which results in frequent disease epidemics.Therefore,a major focus is currently placed on investigating the molecular mechanisms underlying this rapid variation of pathogenicity and coevolving wheat resistance.Limited by the lack of a system for stable transformation of Pst and the difficulties in wheat transformation,it is not easy to generate deeper insights into the wheat-Pst interaction using established genetic methods.Nevertheless,considerable effort has been made to unravel the wheat-Pst interaction and significant progress is being made.Histology and cytology have revealed basic details of infection strategies and defense responses during wheat-Pst interactions,identified cellular components involved in wheat-Pst interactions,and have helped to elucidate their role in the infection process or in plant defense responses.Transcriptome and genome sequencing has revealed the molecular features and dynamics of the wheat-Pst pathosystem.Extensive molecular analyses have led to the identification of major components in the wheat resistance response and in Pst virulence.Studies of wheat-Pst interactions have now entered a new phase in which cellular and molecular approaches are being used.This review focuses on the cellular biology of wheat-Pst interactions and integrates the emerging data from molecular analyses with the histocytological observations.