Manda Yu

Summary Nitric oxide ( NO ), a gaseous, redox‐active small molecule, is gradually becoming established as a central regulator of growth, development, immunity and environmental interactions in plants. A major route for the transfer of NO bioactivity is S ‐nitrosylation, the covalent attachment of an NO moiety to a protein cysteine thiol to form an S‐nitrosothiol ( SNO ). This chemical transformation is rapidly emerging as a prototypic, redox‐based post‐translational modification integral to the life of plants. Here we review the myriad roles of NO and SNO s in plant biology and, where known, the molecular mechanisms underpining their activity. Contents Summary 1142 I. Introduction 1142 II. Routes of NO production 1143 III. Oxidative routes of NO synthesis 1143 IV. Reductive routes of NO synthesis 1144 V. Transfer of NO bioactivity 1144 VI. NO function in plant immunity 1145 VII. Role of NO in hypersensitive cell death 1147 VIII. NO and abiotic stress 1148 IX. NO function in plant development 1149 X. NO contributes to the balancing of growth with development in roots 1149 XI. NO action in root hair development and gravitropic responses 1151 XII. Signalling cross‐talk in roots between NO and ROIs 1151 XIII. NO regulation of root iron homeostasis 1152 XIV. Future perspectives 1152 Acknowledgements 1153 References 1153

Plant genetic transformation heavily relies on the bacterial pathogen Agrobacterium tumefaciens as a powerful tool to deliver genes of interest into a host plant. Inside the plant nucleus, the transferred DNA is capable of integrating into the plant genome for inheritance to the next generation (i.e. stable transformation). Alternatively, the foreign DNA can transiently remain in the nucleus without integrating into the genome but still be transcribed to produce desirable gene products (i.e. transient transformation). From the discovery of A. tumefaciens to its wide application in plant biotechnology, numerous aspects of the interaction between A. tumefaciens and plants have been elucidated. This article aims to provide a comprehensive review of the biology and the applications of Agrobacterium-mediated plant transformation, which may be useful for both microbiologists and plant biologists who desire a better understanding of plant transformation, protein expression in plants, and plant-microbe interaction.

Nitric oxide (NO) is emerging as a key regulator of diverse plant cellular processes. A major route for the transfer of NO bioactivity is S-nitrosylation, the addition of an NO moiety to a protein cysteine thiol forming an S-nitrosothiol (SNO). Total cellular levels of protein S-nitrosylation are controlled predominantly by S-nitrosoglutathione reductase 1 (GSNOR1) which turns over the natural NO donor, S-nitrosoglutathione (GSNO). In the absence of GSNOR1 function, GSNO accumulates, leading to dysregulation of total cellular S-nitrosylation. Here we show that endogenous NO accumulation in Arabidopsis, resulting from loss-of-function mutations in NO Overexpression 1 (NOX1), led to disabled Resistance (R) gene-mediated protection, basal resistance and defence against nonadapted pathogens. In nox1 plants both salicylic acid (SA) synthesis and signalling were suppressed, reducing SA-dependent defence gene expression. Significantly, expression of a GSNOR1 transgene complemented the SNO-dependent phenotypes of paraquat resistant 2-1 (par2-1) plants but not the NO-related characters of the nox1-1 line. Furthermore, atgsnor1-3 nox1-1 double mutants supported greater bacterial titres than either of the corresponding single mutants. Our findings imply that GSNO and NO, two pivotal redox signalling molecules, exhibit additive functions and, by extension, may have distinct or overlapping molecular targets during both immunity and development.