Plant Sciences Department, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK.
Present Address: Curtis Analytics Ltd, Daniel Hall Building, Rothamsted RoCRE, Harpenden, AL5 2JQ, UK.
BMC Genomics. 2019 Aug 1;20(1):628. doi: 10.1186/s12864-019-5991-8.
Free asparagine is the precursor for acrylamide formation during cooking and processing of grains, tubers, beans and other crop products. In wheat grain, free asparagine, free glutamine and total free amino acids accumulate to high levels in response to sulphur deficiency. In this study, RNA-seq data were acquired for the embryo and endosperm of two genotypes of bread wheat, Spark and SR3, growing under conditions of sulphur sufficiency and deficiency, and sampled at 14 and 21 days post anthesis (dpa). The aim was to provide new knowledge and understanding of the genetic control of asparagine accumulation and breakdown in wheat grain.
There were clear differences in gene expression patterns between the genotypes. Sulphur responses were greater at 21 dpa than 14 dpa, and more evident in SR3 than Spark. TaASN2 was the most highly expressed asparagine synthetase gene in the grain, with expression in the embryo much higher than in the endosperm, and higher in Spark than SR3 during early development. There was a trend for genes encoding enzymes of nitrogen assimilation to be more highly expressed in Spark than SR3 when sulphur was supplied. TaASN2 expression in the embryo of SR3 increased in response to sulphur deficiency at 21 dpa, although this was not observed in Spark. This increase in TaASN2 expression was accompanied by an increase in glutamine synthetase gene expression and a decrease in asparaginase gene expression. Asparagine synthetase and asparaginase gene expression in the endosperm responded in the opposite way. Genes encoding regulatory protein kinases, SnRK1 and GCN2, both implicated in regulating asparagine synthetase gene expression, also responded to sulphur deficiency. Genes encoding bZIP transcription factors, including Opaque2/bZIP9, SPA/bZIP25 and BLZ1/OHP1/bZIP63, all of which contain SnRK1 target sites, were also expressed. Homeologues of many genes showed differential expression patterns and responses, including TaASN2.
Data on the genetic control of free asparagine accumulation in wheat grain and its response to sulphur supply showed grain asparagine levels to be determined in the embryo, and identified genes encoding signalling and metabolic proteins involved in asparagine metabolism that respond to sulphur availability.
游离天门冬酰胺是谷物、块茎、豆类和其他作物产品在烹饪和加工过程中形成丙烯酰胺的前体。在小麦籽粒中，游离天门冬酰胺、游离谷氨酰胺和总游离氨基酸在硫缺乏时积累到高水平。在这项研究中，为两种面包小麦基因型 Spark 和 SR3 的胚和胚乳获取了 RNA-seq 数据，这些小麦在硫充足和缺乏的条件下生长，并在授粉后 14 和 21 天（dpa）取样。目的是提供关于小麦籽粒中天冬酰胺积累和分解的遗传控制的新知识和理解。
基因型之间的基因表达模式存在明显差异。21 dpa 时的硫反应大于 14 dpa，在 SR3 中比 Spark 中更明显。TaASN2 是籽粒中表达水平最高的天门冬酰胺合成酶基因，其在胚中的表达远高于胚乳，并且在早期发育过程中在 Spark 中高于 SR3。当硫供应时，编码氮同化酶的基因在 Spark 中的表达趋势高于 SR3。尽管在 Spark 中没有观察到，但 SR3 的胚中 TaASN2 的表达在 21 dpa 时对硫缺乏的反应增加。这种 TaASN2 表达的增加伴随着谷氨酰胺合成酶基因表达的增加和天冬酰胺酶基因表达的减少。胚乳中天冬酰胺合成酶和天冬酰胺酶基因的表达以相反的方式响应。编码调节蛋白激酶 SnRK1 和 GCN2 的基因均参与调节天冬酰胺合成酶基因的表达，它们也对硫缺乏作出反应。编码 bZIP 转录因子的基因，包括 Opaque2/bZIP9、SPA/bZIP25 和 BLZ1/OHP1/bZIP63，都含有 SnRK1 靶标位点，也被表达。许多基因的同源基因表现出不同的表达模式和反应，包括 TaASN2。
关于小麦籽粒中天冬酰胺积累的遗传控制及其对硫供应的反应的数据表明，籽粒中天冬酰胺水平由胚决定，并确定了参与天冬酰胺代谢并对硫可用性作出反应的信号和代谢蛋白的编码基因。
