Like fungi and some prokaryotes, plants use a thiazole synthase (THI4) to make the thiazole precursor of thiamin. Fungal THI4s are suicide enzymes that destroy an essential active-site Cys residue to obtain the sulfur atom needed for thiazole formation. In contrast, certain prokaryotic THI4s have no active-site Cys, use sulfide as sulfur donor, and are truly catalytic. The presence of a conserved active-site Cys in plant THI4s and other indirect evidence implies that they are suicidal. To confirm this, we complemented the Arabidopsistz-1 mutant, which lacks THI4 activity, with a His-tagged Arabidopsis THI4 construct. LC–MS analysis of tryptic peptides of the THI4 extracted from leaves showed that the active-site Cys was predominantly in desulfurated form, consistent with THI4 having a suicide mechanism in planta. Unexpectedly, transcriptome data mining and deep proteome profiling showed that barley, wheat, and oat have both a widely expressed canonical THI4 with an active-site Cys, and a THI4-like paralog (non-Cys THI4) that has no active-site Cys and is the major type of THI4 in developing grains. Transcriptomic evidence also indicated that barley, wheat, and oat grains synthesize thiamin de novo, implying that their non-Cys THI4s synthesize thiazole. Structure modeling supported this inference, as did demonstration that non-Cys THI4s have significant capacity to complement thiazole auxotrophy in Escherichia coli. There is thus a prima facie case that non-Cys cereal THI4s, like their prokaryotic counterparts, are catalytic thiazole synthases. Bioenergetic calculations show that, relative to suicide THI4s, such enzymes could save substantial energy during the grain-filling period.

Like fungi and some prokaryotes, plants use a thiazole synthase (THI4) to make the thiazole precursor of thiamin. Fungal THI4s are suicide enzymes that destroy an essential active-site Cys residue to obtain the sulfur atom needed for thiazole formation. In contrast, certain prokaryotic THI4s have no active-site Cys, use sulfide as sulfur donor, and are truly catalytic. The presence of a conserved activesite Cys in plant THI4s and other indirect evidence implies that they are suicidal. To confirm this, we complemented the Arabidopsis tz-1 mutant, which lacks THI4 activity, with a His-tagged Arabidopsis THI4 construct. LC-MS analysis of tryptic peptides of the THI4 extracted from leaves showed that the active-site Cys was predominantly in desulfurated form, consistent with THI4 having a suicide mechanism in planta. Unexpectedly, transcriptome datamining and deep proteome profiling showed that barley, wheat, and oat have both a widely expressed canonical THI4 with an active-site Cys, and a THI4-like paralog (non-Cys THI4) that has no active-site Cys and is the major type of THI4 in developing grains. Transcriptomic evidence also indicated that barley, wheat, and oat grains synthesize thiamin de novo, implying that their non-Cys THI4s synthesize thiazole. Structure modeling supported this inference, as did demonstration that non-Cys THI4s have significant capacity to complement thiazole auxotrophy in Escherichia coli. There is thus a prima facie case that non-Cys cereal THI4s, like their prokaryotic counterparts, are catalytic thiazole synthases. Bioenergetic calculations show that, relative to suicide THI4s, such enzymes could save substantial energy during the grain filling period. Short title: Suicidal and catalytic plant THI4 enzymes

Peach (Prunus persica) production in the southeastern United States extends from mid-May to mid-September. There are ≈60 peach cultivars commercially grown. Each cultivar has unique fruit quality characteristics, which could influence consumer perception and likability. The present study is a survey of chemical and physical characteristics of mature, commercially grown, fresh peaches in Georgia. A collection of 30 cultivars was evaluated in 2015 and 2016 for soluble solids concentration (SSC), total titratable acidity (TTA), SSC/TTA ratio, texture (compression, puncture, and Kramer shear), and skin and flesh color (CIE L*, chroma, and hue color space values). There was significant variation between seasons for all variables (P < 0.05) except for TTA (P = 0.12), and flesh hue values (P = 0.38). Statistical differences among cultivars within each year were reported for all variables (P < 0.0001). SSC showed variation seasonally and among cultivars, whereas TTA variation was mainly attributed to cultivar differences. Similarly, cultivar-to-cultivar differences were found when comparing the different texture tests evaluated with cultivars such as Goldprince, Early August Prince, Flameprince, Majestic, and Red Globe having the most variation between seasons. Other cultivars analyzed had little variation between seasons. Moreover, firmness differences observed across the three texture tests were inconsistent. In peach skin color, significant variation was observed for L*, chroma, and hue among cultivars. Skin hue and chroma were highly correlated within each season (r = 0.77 for 2015, r = 0.72 for 2016). The results of this survey demonstrate the variation of quality characteristics for a large selection of peach cultivars grown in Georgia. The information reported in this paper will be used as a baseline for further examining and understanding peach fruit quality.

A universal lexicon to describe the appearance, aroma/flavors, and textures/feeling factors of peaches was developed. The objective was to provide a standardized lexicon for descriptive validation. A trained descriptive panel established 29 attributes using 51 peach cultivars grown throughout the production season. This lexicon includes 18 aroma and flavor attributes to describe mature peaches as well as under‐ripe and over‐ripe, redness of flesh for appearance, three feeling factors, and seven terms for describing textures. Principal component analysis was used to discern if differences were found among peach samples using the lexicon terms utilized by trained panelists. Texture was the primary differentiating factor in the first dimension of the biplot followed by peach‐identity in the second dimension. Additionally, the attributes “peach‐identity,” “fruity,” “sweet,” “tart,” “citrus,” “sour,” along with textures and feeling factors were prominent in all peach varieties. This lexicon can be useful to identify and quantify sensory attributes in fresh peaches for food and agriculture research. Practical applications The assessment of peach fruit varieties grown throughout the southeastern United States would create a basis for understanding the prominent and unique characteristics of peach varieties and their inherited variability. The peach lexicon created in this study will provide a platform for researchers and producers to understand the desirable sensory traits in peaches. It will allow comparisons among varieties currently available, create a database to be used in breeding applications, and help the growers to produce peaches with desirable sensory traits that could be commercially successful.

Peach production in Georgia, USA, extends from mid-May to mid-August. Multiple cultivars are commercially grown in the U.S., and each cultivar has unique fruit quality characteristics, which could influence consumer perception and acceptability. Among those, peach flavor has been minimally characterized among cultivars. Headspace-solid phase microextraction (HS–SPME) combined with gas chromatography–mass spectrometry (GC–MS) was used to characterize the volatile profile of 42 peach cultivars commercially grown in 2016. The goal of this research was to understand the aroma composition and content of peach cultivars grown in Georgia, USA. Thirty-six volatile compounds were identified. Significant differences (p ≤ 0.0001) were observed for all the flavor volatiles across all cultivars being evaluated. Esters were the major compounds isolated from the 42 peach cultivars, followed by lactones, alcohols, aldehydes, and terpenoids, in that order. Lactones, benzaldehyde, and linalool, which are known to be peach aroma compounds, exhibited the highest mean concentrations among the cultivars with ɣ- and δ-decalactones having a concentration of approximately 180 ng·g−1 and 60 ng·g−1, respectively. Among the cultivars, “Majestic” had the highest mean concentration of ɣ-decalactone, followed by “Southern Pearl” with approximately 503 ng·g−1 and 443 ng·g−1, respectively. “Southern Pearl” and “Fairtime” also exhibited the highest average concentration of δ-decalactone. The results obtained will help provide an understanding of the distribution of the various volatile organic compounds found in Georgia-grown peach cultivars.