谷子类胡萝卜素生物合成途径SiLCYB基因与米色形成的关系

The Relationship between the Gene SiLCYB Related to Carotenoid Synthesis and the Colored Formation of Foxtail Millet

谷子是中国北方重要杂粮作物,米色是评价谷子品质的重要指标,目前关于谷子米色的形成机制仍不明确。本研究选用米色分别为深黄、浅黄、白色和绿色的谷子品种各2个,对这8个谷子品种进行了总类胡萝卜素含量、β-胡萝卜素含量与米色差异间关系的分析,以及分子水平4个β-胡萝卜素代谢相关基因在籽粒不同灌浆阶段的表达模式分析,结果表明:CCI指数作为米色测定的综合指标,可对不同品种米色差异进行鉴定,且分别与总类胡萝卜素、β-胡萝卜素含量呈显著与极显著正相关。通过对8个品种SiLCYB基因组DNA克隆发现,只有深黄品种JG21中出现序列变异,有两个SNP位点,且第二处单核苷酸变异使相应氨基酸由谷氨酰胺变为精氨酸。SiLCYB表达不具有组织特异性,在叶中表达最高,茎中最低。通过对籽粒不同灌浆阶段β-胡萝卜素合成基因SiLCYB与另外3个β-胡萝卜素代谢相关基因(SiLCYBLCYE,SiHYD,SiCCD1)的表达分析发现:SiLCYB在大多数品种中表达基本恒定,且与β-胡萝卜素积累没有表现出显著相关性;而SiLCYE在不同品种中普遍呈现出与SiLCYB同增同减的表达模式,但表达水平低于SiLCYB;同时发现2个降解相关基因(SiHYD,SiCCD1)的表达与β-胡萝卜素积累在灌浆特定阶段表现出了显著或极显著负相关。因此,推测SiLCYB与降解基因SiHYD和SiCCD1共同作用,通过影响β-胡萝卜素和总类胡萝卜素在籽粒中的积累,进而影响米色的形成。

Foxtail millet is an important minor crop in Northern China, hulless grain color is a key visual index to evaluate foxtail millet quality, but the formation mechanism of hulless grain color remains unclear. Here, eight foxtail millet cultivars were selected including dark and light yellow, white and green foxtail millet varieties, with two cultivars of each color. We mainly analyzed the relationship between the content of total carotenoid andβ-carotene and the color difference of foxtail millet grain, and the expression patterns of four genes related toβ-carotene metabolism at different filling stages of different foxtail millet varieties. The results showed that citrus color index(CCI), as a comprehensive index for the analysis of grain color, is effective on identification of color difference, CCI also showed the significantly positive correlation with the content of total carotenoid and extremely significant positive correlation with the content of β-carotene. Next, the sequence alignment of SiLCYB in eight cultivars was analyzed, and the sequence variations only occurred in JG21, with two SNP(single nucleotide polymorphism) loci, and the second one led to changes in amino acids, with glutamine replaced with arginine. Moreover, the expression of SiLCYB wasn't tissue specific, with the highest expression in leaves and the lowest expression in stem. The expression patterns of SiLCYB and three other genes related to β-carotene metabolism(SiLCYE, SiHYD, SiCCD1) at different filling stages were further analyzed, the results showed that the expression of SiLCYB was almost constant and there is no significantly positive correlation between the expression of SiLCYB and the accumulation of β-carotene. The expression patterns of SiLCYE were similar to SiLCYB, with lower expression level than SiLCYB. Meanwhile, it was discovered that the relative expression level of SiHYD and SiCCD1 related to carotenoid degradation showed significant and highly significant negative correlation at specific stages during filling. Therefore, the formation of different hulless grain color might be caused by the mutual interaction of SiLCYB, SiCCD1 and SiHYD, with differential accumulation of carotenoid and β-carotene.