Soybean [Glycine max (L.) Merr.] contains two proteins called vegetative storage proteins (VSPs) that function as temporary storage reserves, but are also closely related to plant acid phosphatases of the haloacid dehalogenase (HAD) superfamily. This study examined the biochemical basis for the relatively low catalytic activity previously reported for these VSPs. The specific activity of purified recombinant VSPalpha on GMP was about 40-fold lower than for a related soybean root nodule acid phosphatase (APase), which had a specific activity of 845 U mg(-1) protein. Conversion of Ser106 to Asp increased VSPalpha activity about 20-fold. This Asp residue is present in nodule APase and is a highly conserved nucleophile in the HAD superfamily. Related VSPs from cultivated soybean and from three wild perennial soybeans, as well as a pod storage protein (PSP) from Phaseolus vulgaris L. all lack the catalytic Asp, suggesting they too are catalytically inefficient. Phylogenetic analysis showed the VSPs and PSP are more closely related to each other than to 21 other VSP-like proteins from several plant species, all of which have the nucleophilic Asp. This study suggests that loss of catalytic activity may be a requirement for the VSPs and PSP to function as storage proteins in legumes.

The import of ATP into plastids is facilitated by members of the plastidic ATP/ADP transporter (AATP) family. Our results indicate that the cassava (Manihot esculenta Crantz) genome possesses two genes encoding for putative ATP/ADP translocases, which we have designated as MeAATP1 and MeAATP2. Their deduced products are 92 % identical, and phylogenetic reconstructions of plant AATP sequences suggest that MeAATP1 and MeAATP2 are the result of a relatively recent duplication event. Both genes were found to be expressed in a wide range of plant organs via RT-PCR, including young and mature leaves, fibrous and tuberous roots, and green stems. Neither MeAATP1 nor MeAATP2 showed evidence of increased transcription in the presence of exogenous sucrose. Interestingly, the transcriptional activity of MeAATP1 in leaves appeared to be upregulated after wounding, potentially indicating its involvement in the wound response mechanism of cassava.

Somatic embryogenesis provides a useful tool to facilitate efficient mass propagation in plants. The SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE (SERK) gene serves a fundamentally important role in somatic embryogenesis of many plant species. The isolation of a SERK gene homolog, namely CaSERK, from Curcuma alismatifolia Gagnep. cv. Blue Tung, was reported. Prediction of coding sequence showed that it encoded a protein of 628 amino acids showing high similarity to previously characterized SERK sequences and containing all the features shared by members of the SERK family, including five leucine-rich repeats and the distinctive proline-rich SPP domain. Investigation of CaSERK expression revealed that its transcripts were found throughout the whole somatic embryogenesis process with highest abundance in embryogenic callus. These results indicate that CaSERK might have somatic embryogenesis-associated functions in this economically important ornamental ginger. Detection of CaSERK transcript accumulation in flower and coma bract tissues is suggestive of its additional roles in other developmental signaling pathways.