Kim Ga-Eun, Kim Me-Sun, Sung Jwakyung
Department of Crop Science, Chungbuk National University, Cheongju 28644, Korea.
Plants (Basel). 2022 Jun 20;11(12):1618. doi: 10.3390/plants11121618.
Global warming accelerates the destruction of the ozone layer, increasing the amount of UVB reaching the Earth's surface, which in turn alters plant growth and development. The effects of UVB-induced alterations of plant secondary and cell wall metabolism were previously documented; however, there is little knowledge of its effects on rice seedlings during the developmental phase of leaves. In this study, we examined secondary metabolic responses to UVB stress using a transcriptomic approach, focusing on the biosynthetic pathways for lignin, flavonoid, and indole/tryptophan-auxin responses. As new leaves emerged, they were irradiated with UVB for 5 days (for 3 h/day). The genes encoding the enzymes related to lignin (4CL, CAD, and POD) and flavonoid biosynthesis (CHS, CHI, and FLS) were highly expressed on day 1 (younger leaves) and day 5 (older leaves) after UVB irradiation. The expression of the genes encoding the enzymes related to tryptophan biosynthesis (AS, PRT, PRAI, IGPS, and TS) increased on day 3 of UVB irradiation, and the level of tryptophan increased and showed the same temporal pattern of occurrence as the expression of the cognate gene. Interestingly, the genes encoding BBX4 and BBX11, negative regulators of UVB signaling, and SAUR27 and SAUR55, auxin response enzymes, were downregulated on day 3 of UVB irradiation. When these results are taken together, they suggest that secondary metabolic pathways in rice seedlings are influenced by the interaction between UVB irradiation and the leaf developmental stage. Thus, the strategies of protection against, adaptation to, and mitigation of UVB might be delicately regulated, and, in this context, our data provide valuable information to understand UVB-induced secondary metabolism in rice seedlings.
全球变暖加速臭氧层破坏，增加到达地球表面的中波紫外线（UVB）量，进而改变植物的生长发育。此前已有文献记载UVB诱导植物次生代谢和细胞壁代谢改变的影响；然而，对于其在叶片发育阶段对水稻幼苗的影响却知之甚少。在本研究中，我们采用转录组学方法研究了水稻幼苗对UVB胁迫的次生代谢响应，重点关注木质素、类黄酮和吲哚/色氨酸-生长素响应的生物合成途径。新叶长出后，对其进行为期5天（每天3小时）的UVB照射。编码与木质素（4-香豆酸辅酶A连接酶、肉桂醇脱氢酶和过氧化物酶）和类黄酮生物合成（查尔酮合酶、查尔酮异构酶和黄酮醇合酶）相关酶的基因在UVB照射后的第1天（较幼嫩叶片）和第5天（较成熟叶片）高度表达。编码与色氨酸生物合成相关酶（天冬氨酸激酶、磷酸核糖转移酶、磷酸核糖氨基咪唑羧化酶、吲哚甘油磷酸合酶和色氨酸合酶）的基因在UVB照射第3天表达增加，色氨酸水平升高，且呈现出与同源基因表达相同出现时间模式。有趣的是，编码UVB信号负调控因子BBX4和BBX11以及生长素响应酶SAUR27和SAUR55的基因在UVB照射第3天表达下调。综合这些结果表明，水稻幼苗的次生代谢途径受UVB照射与叶片发育阶段相互作用的影响。因此，针对UVB的防护、适应和缓解策略可能受到精细调控，在此背景下，我们的数据为理解UVB诱导的水稻幼苗次生代谢提供了有价值的信息。
