RRFT1 (Redox Responsive Transcription Factor 1) is involved in extracellular ATP-regulated gene expression in Arabidopsis thaliana seedlings

Arabidopsis Transcriptomics Reveals the Role of Lipoxygenase2 (AtLOX2) in Wound-Induced Responses

In wounded Arabidopsis thaliana leaves, four 13S-lipoxygenases (AtLOX2, AtLOX3, AtLOX4, AtLOX6) act in a hierarchical manner to contribute to the jasmonate burst. This leads to defense responses with LOX2 playing an important role in plant resistance against caterpillar herb-ivory. In this study, we sought to characterize the impact of AtLOX2 on wound-induced phytohormonal and transcriptional responses to foliar mechanical damage using wildtype (WT) and lox2 mutant plants. Compared with WT, the lox2 mutant had higher constitutive levels of the phytohormone salicylic acid (SA) and enhanced expression of SA-responsive genes. This suggests that AtLOX2 may be involved in the biosynthesis of jasmonates that are involved in the antagonism of SA biosynthesis. As expected, the jasmonate burst in response to wounding was dampened in lox2 plants. Generally, 1 h after wounding, genes linked to jasmonate biosynthesis, jasmonate signaling attenuation and abscisic acid-responsive genes, which are primarily involved in wound sealing and healing, were differentially regulated between WT and lox2 mutants. Twelve h after wounding, WT plants showed stronger expression of genes associated with plant protection against insect herbivory. This study highlights the dynamic nature of jasmonate-responsive gene expression and the contribution of AtLOX2 to this pathway and plant resistance against insects.

Growth regulation by apyrases: Insights from altering their expression level in different organisms

Apyrase (APY) enzymes are nucleoside triphosphate (NTP) diphosphohydrolases that can remove the terminal phosphate from NTPs and nucleoside diphosphates but not from nucleoside monophosphates. They have conserved structures and functions in yeast, plants, and animals. Among the most studied APYs in plants are those in Arabidopsis (Arabidopsis thaliana; AtAPYs) and pea (Pisum sativum; PsAPYs), both of which have been shown to play major roles in regulating plant growth and development. Valuable insights on their functional roles have been gained by transgenically altering their transcript abundance, either by constitutively expressing or suppressing APY genes. This review focuses on recent studies that have provided insights on the mechanisms by which APY activity promotes growth in different organisms. Most of these studies have used transgenic lines that constitutively expressed APY in multiple different plants and in yeast. As APY enzymatic activity can also be changed post-translationally by chemical blockage, this review also briefly covers studies that used inhibitors to suppress APY activity in plants and fungi. It concludes by summarizing some of the main unanswered questions about how APYs regulate plant growth and proposes approaches to answering them.

Advances in chilling injury of postharvest fruit and vegetable: Extracellular ATP aspects

Due to the global use of cold chain, the development of postharvest technology to reduce chilling injury (CI) in postharvest fruits and vegetables during storage and transport is needed urgently. Considerable evidence shows that maintaining intracellular adenosine triphosphate (iATP) in harvested fruits and vegetables is beneficial to inhibiting CI occurrence. Extracellular ATP (eATP) is a damage-associated signal molecule and plays an important role in CI of postharvest fruits and vegetables through its receptor and subsequent signal transduction under low-temperature stress. The development of new aptasensors for the simultaneous determination of eATP level allows for better understanding of the roles of eATP in a myriad of responses mediated by low-temperature stress in relation to the chilling tolerance of postharvest fruits and vegetables. The multiple biological functions of eATP and its receptors in postharvest fruits and vegetables were attributed to interactions with reactive oxygen species (ROS) and nitric oxide (NO) in coordination with phytohormones and other signaling molecules via downstream physiological activities. The complicated interconnection among eATP in relation to its receptors, eATP/iATP homeostasis, ROS, NO, and heat shock proteins triggered by eATP recognition has been emphasized. This paper reviews recent advances in the beneficial effects of energy handling, outlines the production and homeostasis of eATP, discusses the possible mechanism of eATP and its receptors in chilling tolerance, and provides future research directions for CI in postharvest fruits and vegetables during low-temperature storage.

Recent Advances Clarifying the Structure and Function of Plant Apyrases (Nucleoside Triphosphate Diphosphohydrolases)

Studies implicating an important role for apyrase (NTPDase) enzymes in plant growth and development began appearing in the literature more than three decades ago. After early studies primarily in potato, Arabidopsis and legumes, especially important discoveries that advanced an understanding of the biochemistry, structure and function of these enzymes have been published in the last half-dozen years, revealing that they carry out key functions in diverse other plants. These recent discoveries about plant apyrases include, among others, novel findings on its crystal structures, its biochemistry, its roles in plant stress responses and its induction of major changes in gene expression when its expression is suppressed or enhanced. This review will describe and discuss these recent advances and the major questions about plant apyrases that remain unanswered.

Annexin 1 Is a Component of eATP-Induced Cytosolic Calcium Elevation in Arabidopsis thaliana Roots

Extracellular ATP (eATP) has long been established in animals as an important signalling molecule but this is less understood in plants. The identification of Arabidopsis thaliana DORN1 (Does Not Respond to Nucleotides) as the first plant eATP receptor has shown that it is fundamental to the elevation of cytosolic free Ca²⁺ ([Ca²⁺]_cyt) as a possible second messenger. eATP causes other downstream responses such as increase in reactive oxygen species (ROS) and nitric oxide, plus changes in gene expression. The plasma membrane Ca²⁺ influx channels involved in eATP-induced [Ca²⁺]_cyt increase remain unknown at the genetic level. Arabidopsis thaliana Annexin 1 has been found to mediate ROS-activated Ca²⁺ influx in root epidermis, consistent with its operating as a transport pathway. In this study, the loss of function Annexin 1 mutant was found to have impaired [Ca²⁺]_cyt elevation in roots in response to eATP or eADP. Additionally, this annexin was implicated in modulating eATP-induced intracellular ROS accumulation in roots as well as expression of eATP-responsive genes.