In vivo haploid induction has been extended from maize to monocotyledonous plants like rice, wheat, millet and dicotyledonous plants such as tomato, rapeseed, tobacco and cabbage. Accurate identification of haploids is a crucial step of doubled haploid technology, where a useful identification marker is very pivotal. R1-nj is an extensively used visual marker for haploid identification in maize. RFP and eGFP have been shown to be feasible in identifying haploid. However, these methods are either limited to specific species, or require specific equipment. It still lacks an efficient visual marker that is practical across different crop species. In this study, we introduced the RUBY reporter, a betalain biosynthesis system, into maize and tomato haploid inducers as a new marker for haploid identification. Results showed that expression of RUBY could result in deep betalain pigmentation in maize embryos as early as 10 days after pollination, and enabled 100% accuracy of immature haploid embryo identification. Further investigation in tomato revealed that the new marker led to deep red pigmentation in radicles and haploids can be identified easily and accurately. The results demonstrated that the RUBY reporter is a background-independent and efficient marker for haploid identification and would be promising in doubled haploid breeding across different crop species.

中文翻译：

---

RUBY 报告基因能够有效识别玉米和番茄的单倍体

体内单倍体诱导已从玉米扩展到单子叶植物如水稻、小麦、小米和双子叶植物如番茄、油菜籽、烟草和卷心菜。单倍体的准确鉴定是双单倍体技术的关键一步，其中有用的识别标记非常关键。R1-nj是一种广泛用于玉米单倍体鉴定的视觉标记。RFP 和 eGFP 已被证明在鉴定单倍体方面是可行的。然而，这些方法要么仅限于特定物种，要么需要特定设备。它仍然缺乏适用于不同作物种类的有效视觉标记。在这项研究中，我们将RUBY报告基因（一种甜菜碱生物合成系统）引入玉米和番茄单倍体诱导剂中，作为单倍体鉴定的新标记。结果表明，RUBY的表达早在授粉后 10 天就可以在玉米胚胎中产生较深的甜菜碱色素沉着，并使未成熟单倍体胚胎鉴定的准确性达到 100%。对番茄的进一步研究表明，新标记导致胚根和单倍体中深红色色素沉着，可以轻松准确地识别。结果表明，RUBY报告基因是单倍体鉴定的背景无关且有效的标记，并且在不同作物物种的双单倍体育种中具有广阔的前景。