提出问题：However, our understanding of the molecular mechanisms governing ovule development is far from complete.

研究基础：In Arabidopsis, ovule identity is determined by homeotic MADS‐domain proteins that define the floral C‐ (AG) and D‐ (SHP1/SHP2, STK) functions. Pre‐mRNA processing of these genes is critical and mediated by HUA‐PEPactivity, composed of genes encoding RNA‐inding proteins.In strong hua‐pep mutants, functional transcripts for C‐ and D‐function genes are reduced, resulting in homeotic transformation of ovules. Thus, hua‐pep mutants provide an unique sensitized background to study ovule morphogenesis when C‐ and D‐functions are simultaneously compromised. 

结果：We found that hua‐pep ovules are morphologically sepaloid and show ectopic expression of the homeotic class‐A gene AP1. Inactivation of AP1 or AP2 (A‐function genes) in hua‐pep mutants reduced homeotic conversions, rescuing ovule identity while promoting carpelloid traits in transformed ovules. Interestingly, increased AG dosage led to similar results. 

Fig. 7 Model for ovule identity determination by antagonistic A and C + D floral activities in Arabidopsis.

结论：Our findings strongly suggest that HUA‐PEP activity is required for correct C and D floral functions, which in turn prevents ectopic expression of class‐A genes in ovules for their proper morphogenesis, evoking the classic A–C antagonism of the ABC model for floral organ development.