Hypocotyl length is regarded to be a crucial seedling trait, influencing many subsequent plant development processes. However, little is known about this trait in Brassica campestris syn. Brasscia rapa. Here, we performed a comparative observation on the early hypocotyl development between two cultivars, ‘SZQ’ belonging to pak-choi (B. campestris ssp. chinensis var. communis) with longer hypocotyls, and ‘WTC’ belonging to Tacai (B. campestris L. ssp. chinensis var. rosularis) with shortter hypocotyls, and found that the difference in auxin biosynthesis might contribute to the varied hypocotyl phenotype between these two cultivars. By applying GWAS analysis using a total of 226 B. campestris accessions, we identified that the AT-Hook motif nuclear localized (AHL) gene BcAHL24-MF1 contributed to the natural variation in hypocotyl length. Functional variation of BcAHL24-MF1 was attributed to four haplotypes featuring four SNPs within the promoter region, of which Hap I accumulated more transcripts with shorter hypocotyls. Constitutive overexpression of BcAHL24-MF1 in B. campestris caused decreased hypocotyl length under light circumstances and even constant darkness, as BcAHL24-MF1 repressed the PIF-mediated transcriptional activation of auxin biosynthesis genes BcYUC6-MF2 and BcYUC8-LF. Our research uncovered the important role of BcAHL24-MF1 in regulating light-triggered inhibition of hypocotyl elongation, therefore presenting a valuable genetic target for crop breeding.

中文翻译：

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BcAHL24-MF1 通过抑制光照条件下下胚轴的过度伸长促进油菜的光形态发生


下胚轴长度被认为是一种重要的幼苗性状，影响着许多后续的植物发育过程。然而，对 Brassica campestris syn. Brasscia rapa 的这一特性知之甚少。在这里，我们对两个品种之间的早期下胚轴发育进行了比较观察，'SZQ' 属于下胚轴较长的白菜 （B. campestris ssp. chinensis var. communis） 和属于塔彩 （B. campestris L. ssp. chinensis var. rosularis） 的 'WTC' 下胚轴较短，发现生长素生物合成的差异可能导致这两个品种之间的下胚轴表型不同。通过使用总共 226 个 B. campestris 种质进行 GWAS 分析，我们确定 AT-Hook 基序核定位 （AHL） 基因 BcAHL24-MF1 有助于下胚轴长度的自然变化。BcAHL24-MF1 的功能变异归因于启动子区域内具有 4 个 SNP 的 4 个单倍型，其中 Hap I 积累了更多下胚轴较短的转录本。BcAHL24-MF1 在油菜中组成型过表达导致在光照甚至持续黑暗下下胚轴长度减少，因为 BcAHL24-MF1 抑制了 PIF 介导的生长素生物合成基因 BcYUC6-MF2 和 BcYUC8-LF 的转录激活。我们的研究揭示了 BcAHL24-MF1 在调节光触发的下胚轴伸长抑制中的重要作用，因此为作物育种提供了有价值的遗传靶点。