Two novel genes are differentially expressed during early germination of the male gametophyte of Nicotiana tabacum.

Two cDNAs were cloned from tobacco pollen by differential display of mRNAs from dry and germinated pollen. Expression analysis revealed that transcript levels of the two corresponding genes were high during pollen maturation, but differed significantly during early pollen germination. One of the cDNAs, designated Arpl1;1, codes for a new member of the auxin-repressed/dormancy-associated protein multigene family. High Arpl1;1 transcript levels correlated with pollen maturation. In germinating pollen, transcripts rapidly declined to minimal levels. The second cDNA, designated Mads1;11, codes for a novel transcription factor exhibiting a novel structure for a putative MADS box protein from plants. Transient expression of a chimeric gene encoding the N-terminal part of Mads1;11 fused to the green fluorescent protein (GFP) in onion epidermal cells revealed that the protein was localized to the nucleus, consistent with its presumed function as a transcriptional regulator. Mads1;11 mRNA abundance was high in mature pollen and, in contrast to Arpl1;1, remained high during 6 h of in vitro pollen germination. The data indicate differential regulation of mRNA concentrations during pollen germination and suggest a function of Mads1;11 protein in regulating gene expression during early pollen tube growth.