New microsome-associated HT-family proteins from Nicotiana respond to pollination and define an HT/NOD-24 protein family

摘要

HT-family proteins have been identified in Nicotiana, Solanum,and Petunia.HT-B-type proteins are implicated in S-RNase-based self-incompatibility,but the functions of other family members are unknown.Screening for cDNA sequences with an expression pattern similar to HT-B in Nicotiana alata revealed a new group of small HT-family proteins.designated HT-M.HT-M proteins resemble HT-B in several respects:their pistil-specific expression pattern iS indistinguish-able from HT-B,they pellet with a microsome fraction,and their abundance decreases after pollination.Unlike HT-B,there iS no S-specificity to this response,and RNAi experiments show that HT-M proteins are not necessary for self-incompatibility.Identification of a third group of pistil-specific HT-family proteins helps better define the characteristics of the family and allowed identification of putative new family members.By searching the databases with only the most conserved HT-family sequence elements,the signal sequence and cysteine motifs,we identified nodulin-24-1ike proteins and several small glycine-rich proteins as putative HT-family members.Like HT-M and HT-B,nodulin-24 iS membrane associated.We propose that the conserved features in HT-family proteins are important for targeting or modification and refer to the broader family that includes both HT-and nodulin-24-like proteins as the HT/NOD-24-family.