Arabidopsis NF‐YB subunits LEC1 and LEC1‐LIKE activate transcription by interacting with seed‐specific ABRE‐binding factors

Abstract

Summary: LEAFY COTYLEDON 1 (LEC1) plays vital roles in the regulation of seed maturation in Arabidopsis. LEC1 encodes a homolog of yeast HAP3 or mammalian NF‐YB/CBF‐A subunit of trimeric CCAAT binding factor (CBF). Among the nine paralogs of NF‐YB in Arabidopsis, LEC1‐LIKE (L1L) is most closely related to LEC1, and can complement the lec1 mutation when expressed under the control of the LEC1 promoter. Although the nature of the B3‐type seed maturation regulators as transcription factors have been investigated, knowledge of the molecular action of LEC1 is limited. When co‐expressed with NF‐YC2 in the presence of ABA, we found that LEC1 or L1L, but not other NF‐YBs, activated the promoter of CRUCIFERIN C (CRC), which encodes a seed storage protein. However, additional expression of an NF‐YA subunit interfered with the activation. The LEC1/L1L‐[NF‐YC2] activation depended on ABA‐response elements present in the promoter, which led to the finding that LEC1/L1L‐[NF‐YC2] can strongly activate the CRC promoter in the absence of ABA when co‐expressed with a seed‐specific ABA‐response element (ABRE)‐binding factor, bZIP67. Functional coupling of LEC1/L1L‐[AtNF‐YC2] and bZIP67 was also observed in the regulation of sucrose synthase 2 (SUS2). Immunoprecipitation experiments revealed that L1L and bZIP67 formed a protein complex in vivo. These results demonstrate a novel plant‐specific mechanism for NF‐Y subunit function that enables LEC1 and L1L to regulate a defined developmental network.