Haploids can be induced in knockout mutants of OsPLA1, but not OsDMP3 or OsDMP6, in rice

Doubled haploid (DH) technology is an important tool in crop breeding because it can significantly accelerate the breeding process. ZmPLA1/MATL/NLD and ZmDMP are two key genes controlling haploid induction (HI) in maize, exhibiting a synergistic effect. However, it is unknown whether knock out of ZmDMP orthologs can stimulate HI in rice. In this study, a ZmPLA1 ortholog (OsPLA1) and two ZmDMP orthologs (OsDMP3 and OsDMP6) were identified in rice. All three genes encode plasma membrane-localized proteins and were highly expressed in mature anthers. Knockout of OsPLA1 in both Minghui 63 and Nipponbare resulted in reduced seed setting rate (SSR) and caused HI. The osdmp3, osdmp6 and the double mutant failed to trigger HI independently, nor increased the haploid induction rate (HIR) when combined with ospla1. Repeated pollinations operations of QX654A with the ospla1 mutant significantly improve SSR, while reducing HIR. RNA-seq profiling of mature ospla1 mutant anthers indicated that a large number of differentially expressed genes (DEGs) were enriched in redox homeostasis and lipid metabolic GO terms, plant hormone signal transduction, and MAPK signaling pathways. These findings provide important insights towards construction of an efficient DH breeding technology and study of the molecular mechanism of HI in rice.