Nguyen Nguyen Hoai, Sng Benny Jian Rong, Yeo Hock Chuan, Jang In-Cheol
Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, Singapore, 117604, Singapore.
Department of Biological Sciences, National University of Singapore, Singapore, 117543, Singapore.
BMC Genomics. 2021 Oct 25;22(1):760. doi: 10.1186/s12864-021-08076-1.
Plants grown under shade are exposed to low red/far-red ratio, thereby triggering an array of altered phenotypes called shade avoidance syndrome (SAS). Shade negatively influences plant growth, leading to a reduction in agricultural productivity. Understanding of SAS is crucial for sustainable agricultural practices, especially for high-density indoor farming. Brassicaceae vegetables are widely consumed around the world and are commonly cultivated in indoor farms. However, our understanding of SAS in Brassicaceae vegetables and their genome-wide transcriptional regulatory networks are still largely unexplored.
Shade induced common signs of SAS, including hypocotyl elongation and reduced carotenoids/anthocyanins biosynthesis, in two different Brassicaceae species: Brassica rapa (Choy Sum and Pak Choy) and Brassica oleracea (Kai Lan). Phenotype-assisted transcriptome analysis identified a set of genes induced by shade in these species, many of which were related to auxin biosynthesis and signaling [e.g. YUCCA8 (YUC8), YUC9, and INDOLE-3-ACETIC ACID INDUCIBLE (IAAs)] and other phytohormones signaling pathways including brassinosteroids and ethylene. The genes functioning in plant defense (e.g. MYB29 and JASMONATE-ZIM-DOMAIN PROTEIN 9) as well as in biosynthesis of anthocyanins and glucosinolates were repressed upon shade. Besides, each species also exhibited distinct SAS phenotypes. Shade strongly reduced primary roots and elongated petioles of B. oleracea, Kai Lan. However, these SAS phenotypes were not clearly recognized in B. rapa, Choy Sum and Pak Choy. Some auxin signaling genes (e.g. AUXIN RESPONSE FACTOR 19, IAA10, and IAA20) were specifically induced in B. oleracea, while homologs in B. rapa were not up-regulated under shade. Contrastingly, shade-exposed B. rapa vegetables triggered the ethylene signaling pathway earlier than B. oleracea, Kai Lan. Interestingly, shade induced the transcript levels of LONG HYPOCOTYL IN FAR-RED 1 (HFR1) homolog in only Pak Choy as B. rapa. As HFR1 is a key negative regulator of SAS in Arabidopsis, our finding suggests that Pak Choy HFR1 homolog may also function in conferring higher shade tolerance in this variety.
Our study shows that two Brassicaceae species not only share a conserved SAS mechanism but also exhibit distinct responses to shade, which will provide comprehensive information to develop new shade-tolerant cultivars that are suitable for high-density indoor farms.
在遮荫条件下生长的植物会暴露于低红/远红比率，从而引发一系列称为避荫综合征（SAS）的表型变化。遮荫对植物生长产生负面影响，导致农业生产力下降。了解SAS对于可持续农业实践至关重要，特别是对于高密度室内种植而言。十字花科蔬菜在全球广泛消费，并且通常在室内农场种植。然而，我们对十字花科蔬菜中的SAS及其全基因组转录调控网络的了解仍大多未被探索。
遮荫在两种不同的十字花科物种中诱导了SAS的常见迹象，包括下胚轴伸长和类胡萝卜素/花青素生物合成减少：小白菜（菜心和小白菜）和青花菜（芥蓝）。表型辅助转录组分析确定了这些物种中一组由遮荫诱导的基因，其中许多与生长素生物合成和信号传导[例如YUCCA8（YUC8）、YUC9和吲哚-3-乙酸诱导型（IAA）]以及其他植物激素信号传导途径（包括油菜素内酯和乙烯）有关。在遮荫条件下，参与植物防御（例如MYB29和茉莉酸-ZIM结构域蛋白9）以及花青素和芥子油苷生物合成的基因受到抑制。此外，每个物种还表现出不同的SAS表型。遮荫强烈减少了青花菜（芥蓝）的初生根并使叶柄伸长。然而，这些SAS表型在小白菜（菜心和小白菜）中并未明显体现。一些生长素信号基因（例如生长素响应因子19、IAA10和IAA20）在青花菜（芥蓝）中被特异性诱导，而小白菜中的同源基因在遮荫条件下并未上调。相反，暴露于遮荫的小白菜蔬菜比青花菜（芥蓝）更早触发乙烯信号传导途径。有趣的是，遮荫仅在小白菜（作为小白菜）中诱导了远红光下长下胚轴1（HFR1）同源基因的转录水平。由于HFR1是拟南芥中SAS的关键负调节因子，我们的发现表明小白菜HFR1同源基因也可能在赋予该品种更高的耐荫性方面发挥作用。
我们的研究表明，两种十字花科物种不仅共享保守的SAS机制，而且对遮荫表现出不同的反应，这将为开发适合高密度室内农场的新型耐荫品种提供全面信息
