Glagoleva Anastasiia Y, Vikhorev Alexander V, Shmakov Nikolay A, Morozov Sergey V, Chernyak Elena I, Vasiliev Gennady V, Shatskaya Natalia V, Khlestkina Elena K, Shoeva Olesya Y
Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia.
Kurchatov Genomics Center, ICG, SB RAS, Novosibirsk, Russia.
Front Plant Sci. 2022 Jul 11;13:923717. doi: 10.3389/fpls.2022.923717. eCollection 2022.
Barley ( L.) grain pigmentation is caused by two types of phenolic compounds: anthocyanins (which are flavonoids) give a blue or purple color, and melanins (which are products of enzymatic oxidation and polymerization of phenolic compounds) give a black or brown color. Genes and determine the synthesis of purple anthocyanins in the grain pericarp, whereas melanins are formed under the control of the gene in hulls and pericarp tissues. Unlike anthocyanin synthesis, melanin synthesis is poorly understood. The objective of the current work was to reveal features of the phenylpropanoid biosynthesis pathway functioning in melanin-accumulating barley grains. For this purpose, comparative transcriptomic and metabolomic analyses of three barley near-isogenic lines accumulating anthocyanins, melanins, or both in the grain, were performed. A comparative analysis of mRNA libraries constructed for three stages of spike development (booting, late milk, and early dough) showed transcriptional activation of genes encoding enzymes of the general phenylpropanoid pathway in all the lines regardless of pigmentation; however, as the spike matured, unique transcriptomic patterns associated with melanin and anthocyanin synthesis stood out. Secondary activation of transcription of the genes encoding enzymes of the general phenylpropanoid pathway together with genes of monolignol synthesis was revealed in the line accumulating only melanin. This pattern differs from the one observed in the anthocyanin-accumulating lines, where - together with the genes of general phenylpropanoid and monolignol synthesis pathways - flavonoid biosynthesis genes were found to be upregulated, with earlier activation of these genes in the line accumulating both types of pigments. These transcriptomic shifts may underlie the observed differences in concentrations of phenylpropanoid metabolites analyzed in the grain at a late developmental stage by high-performance liquid chromatography. Both melanin-accumulating lines showed an increased total level of benzoic acids. By contrast, anthocyanin-accumulating lines showed higher concentrations of flavonoids and -coumaric and ferulic acids. A possible negative effect of melanogenesis on the total flavonoid content and a positive influence on the anthocyanin content were noted in the line accumulating both types of pigments. As a conclusion, redirection of metabolic fluxes in the phenylpropanoid biosynthesis pathway occurs when melanin is synthesized.
大麦（L.）籽粒色素沉着由两种酚类化合物引起：花青素（属于黄酮类）呈现蓝色或紫色，黑色素（是酚类化合物酶促氧化和聚合的产物）呈现黑色或棕色。基因和决定了籽粒果皮中紫色花青素的合成，而黑色素是在颖壳和果皮组织中的基因控制下形成的。与花青素合成不同，黑色素合成的了解较少。当前工作的目的是揭示在积累黑色素的大麦籽粒中苯丙烷生物合成途径的功能特征。为此，对三个在籽粒中积累花青素、黑色素或两者皆有的大麦近等基因系进行了比较转录组学和代谢组学分析。对为穗发育的三个阶段（孕穗期、乳熟后期和面团期早期）构建的mRNA文库进行的比较分析表明，无论色素沉着情况如何，所有品系中编码一般苯丙烷途径酶的基因都有转录激活；然而，随着穗的成熟，与黑色素和花青素合成相关的独特转录组模式凸显出来。在仅积累黑色素的品系中，发现编码一般苯丙烷途径酶的基因以及单木质醇合成基因的转录二次激活。这种模式不同于在积累花青素的品系中观察到的模式，在积累花青素的品系中，除了一般苯丙烷和单木质醇合成途径的基因外，还发现类黄酮生物合成基因上调，且在积累两种色素的品系中这些基因激活更早。这些转录组变化可能是在发育后期通过高效液相色谱分析籽粒中苯丙烷代谢物浓度时观察到的差异的基础。两个积累黑色素的品系中苯甲酸的总水平都有所增加。相比之下，积累花青素的品系中类黄酮以及对香豆酸和阿魏酸的浓度更高。在积累两种色素的品系中，注意到黑色素生成对总类黄酮含量可能有负面影响，而对花青素含量有正面影响。总之，当合成黑色素时，苯丙烷生物合成途径中的代谢通量会发生重定向。
