In vivo haploid induction leads to increased frequency of twin-embryo and abnormal fertilization in maize

Liwei Liu,Chenxu Liu,Xiaolong Tian,Jinlong Li,Chen Chen,Shaojiang Chen,Baojian Chen,Wei Li

doi:10.1186/s12870-018-1422-2

Abstract

BackgroundIn vivo haploid induction (HI) based on Stock6-derived inducer lines has been the most prevalent means of producing haploids. Nevertheless, the biological mechanism of HI is not fully understood, the twin-embryo kernels had been found during haploid induction, which may provide potential evidence for the abnormal double fertilization during HI.ResultsWe investigated twin-embryo frequency in progenies of different haploid inducers. Results reveal that increasing the HI potential significantly improved the frequency of twin-embryo kernels. Compared with the average twin-embryo kernel frequency (average frequency = 0.07%) among progenies pollinated by the haploid inducer line CAUHOI, the frequency of twin-embryo was improved to 0.16% in progenies pollinated by the haploid inducer line CAU5. This result was further confirmed by pollinating single hybrid ND5598 with four haploid inducers possessing differentiated HIRs, where twin-embryo frequency was highly correlated with HIR. Among 237 twin-embryo kernels, we identified 30 haploid twin-embryo kernels (12.66%), a frequency which was much greater than the average HI rate for three other inducer lines (frequency range 2–10%). In addition, aneuploids, occurred at high frequency (8 in 41 twin plants). This level of aneuploidy provides new insight into the abnormal double fertilization during HI. Moreover, we observed differences in growth rate between twin plants in the field, as 4.22% of the twin plants grew at a significantly different rate. Both simple sequence repeats markers (SSR) and 3072 SNP-chip genotyping results revealed that > 90% of the twin plants shared the same origin, and the growth difference could be attributed to aneuploidy, competition for nutrients, and possible hormone regulation.ConclusionThese results demonstrate that an enhanced HI ability can increase twin-embryo kernel frequency, and high frequency of both haploid twin-embryo kernels and aneuploidy observed in this research give us new insights to understand the mechanism of both HI and abnormal embryogenesis.

Highlights

In vivo haploid induction (HI) based on Stock6-derived inducer lines has been the most prevalent means of producing haploids
Maize haploid inducers increase twin-embryo kernel rate (TEKR) In our first trial that included 17 different maternal inbred lines pollinated with two haploid inducers, we found only 60 twin-embryo kernels (Additional file 1) in 60,659 seeds
This extremely low TEKR did not allow us to establish a definitive connection between a maternal heterotic group and twin-embryo kernel frequency

Summary

Introduction

In vivo haploid induction (HI) based on Stock6-derived inducer lines has been the most prevalent means of producing haploids. The spontaneous development of multiple embryos in maize was originally described by Schrenk [8]. Pesev et al studied the possibility of breeding twin-embryo lines from a synthetic maize population which can significantly increase both protein and oil content compares to single embryo kernels [9]. The frequency of twin-embryo kernels varied from 2.1 to 25.3%, with an average of 11.8%. Another analysis on the twin-embryo phenomenon of maize inbred line VIR17 showed that two types of twin-embryos including both suspensorial embryony and typical cleavage of zygotic proembryo occur spontaneously, typical cleavage can be induced by treatment of developing caryopses with 2, 4-dichlorophenoxyacetic acid (commonly known as 2, 4-D) after pollination [10]

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