ATP, the universal energy currency of all organisms, is released into the extracellular matrix and serves as a signal among cells, where it is referred to as an extracellular ATP. Although a signalling role for extracellular ATP has been well studied in mammals over the last 40 years, investigations of such a role in plants are at an early stage. In this review, Gary Stacey and colleagues highlight the genetic and biochemical evidence for the role of DORN1 in extracellular ATP signalling, placing this within the wider context of extracellular ATP signalling during plant stress responses.
Homocysteine S-methyltransferases (HMTs) are widely distributed enzymes that convert homocysteine (Hcy) into methionine (Met) using either S-adenosylmethionine (AdoMet) or the plant secondary product S-methylmethionine (SMM) as methyl donor. In this paper, Andrew Hanson and colleagues show that bacterial, plant, protistan and animal HMTs likewise prefer (R,S)- over (S,S)-AdoMet, that their ability to use SMM varies greatly and is associated with the likely prevalence of SMM in the environment of the organism, and that most HMTs cannot use S-ribosylMet.
Arabidopsis thaliana has three genes that encode distinct aconitases (ACO), but little is known about the function of each isoenzyme during plant development. In this paper, Mark Hooks and colleagues demonstrate a cytosolic localization of ACO3 in 3-day-old seedlings. This localization, coupled with importance of ACO3 in citrate metabolism, supports the operation of the classic glyoxylate cycle and not direct mitochondrial metabolism of citrate during lipid mobilization in seedlings of oilseed plants, such as Arabidopsis.
The TenA protein family occurs in prokaryotes, plants and fungi; it has two subfamilies, one (TenA_C) having an active-site cysteine, the other (TenA_E) not. TenA_C proteins participate in thiamin salvage by hydrolysing the thiamin breakdown product amino-HMP (4-amino-5-aminomethyl-2-methylpyrimidine) to HMP (4-amino-5-hydroxymethyl-2-methylpyrimidine); the function of TenA_E proteins is unknown. In this paper, Andrew Hanson and colleagues present results which indicate that TenA_E proteins mediate amidohydrolase and aminohydrolase steps in the salvage of thiamin breakdown products; considering that such products can be toxic, TenA_E proteins may also pre-empt toxicity.