**3. The ERD genes studied in soybean**

In respect to ERD genes described in soybean, the behavior of a group of eight genes (ERD1, ERD2, ERD3, ERD9, ERD10, ERD12, ERD15 gene and ERD16) was studied in response to stress. A soybean cDNA ERD1, homologous to yeast Hsp104, was isolated and characterized [46]. The soybean genes encoding homologs to yeast Hsp104 and Hsp101 have a high level of sequence identity to members of the family Clp [46]. When heterologously expressed in yeast, the soybean Hsp101 gene conferred greater thermotolerance to yeast [46]. Several genes related to Hsp70 (ERD2) have been described in soybean using proteomics studies. The first evidence of an ERD2-like protein in soybean was found during heat shock [47]. The presence of similar proteins was also found in response to osmotic and reticulum stress [48]. In respect to the orthologs of ERD3 in soybean, it was found that the GmIMT gene, which encodes a methyltransferase, acts by methylating the substrate D-ononitol. Its overexpres‐ sion in Arabidopsis causes an increase in drought and salinity tolerance [49]. When a gene encoding a soybean GST, an ortholog of ERD9, was over-expressed in tobacco plants, it con‐ ferred an increase in salinity and drought tolerance [50].

Group 2 LEA (dehydrins or responsive to abscisic acid) proteins, such as ERD10 proteins, are postulated to protect macromolecules from damage by freezing, dehydration, ionic, or osmotic stress. In soybean, proteins of this group were studied for their structural and phys‐ io-chemical properties but little is discussed regarding the function of these proteins [51]. Overexpression of a member of the ERD12 family, GmAOC5, significantly increased oxida‐ tive stress resistance [52]. Within the ERD15 family, a soybean ortholog, GmERD15 has been functionally characterized as a transcription factor; in response to osmotic stress, GmERD15 acts to control transcription of a gene related to an integrative pathway in soybean [25]. Fi‐ nally, orthologs of ERD16 studied in soybean genes were identified with differential expres‐ sion during flood stress and hypoxia [53]. All genes studied related to different levels in response to stress, particularly drought and osmotic stress, demonstrating the conservation of function of this gene family in different plant species.

Some ERD genes not yet studied in soybean deserve special attention because of either the proven involvement of a gene with similar functions in drought response in other organ‐ isms, or due to multiple copies of the soybean homolog. ERD5 and ERD7 family members have been characterized by activity in response to drought in other organisms (discussed be‐ low). They have not been studied in soybean; however, homology to soybean genes is dem‐ onstrated by the phylogenic tree shown in Figure 1.

ERD5 (which encodes a precursor of a proline dehydrogenase), has five orthologous genes in soybean. ERD5 has a proven role in drought response due to its role in accumulation of proline [54], a common occurrence during osmotic stress. All soybean genes are clustered in a group distinct from orthologs in other species (Figure 1), which may reflect a possible functional divergence.

ERD7 (which encodes a protein related to senescence and dehydration) has nine orthologous genes in soybean. It also has a central role in response to drought and osmotic stress and it is re‐ lated with drought-induced leaf senescence in plants [55]; regulation of this process during drought tolerance has been studied in depth [55]. Phylogenetic analysis of these genes sug‐ gests the possibility of functional divergence of these genes within the same organism.

**Figure 1.** Relatedness of ERD5 (panel A) and ERD7 (panel B) proteins from different plant species. The multiple align‐ ment was made using ClustalW, and the dendrogram was built with the MEGA5 software using the UPGMA method. The numbers at the nodes indicate the bootstrap scores. The proteins accession numbers are indicated.

### **4. Conclusion**

relative to control plants [44]. Transgenic wheat plants over-expressing TaDi19A, a gene re‐ sponsive to salinity in wheat, exhibited increased expression of ERD15 [45]. In contrast to these findings, Arabidopsis plants over-expressing ERD15 demonstrated susceptibility to drought and freezing [35]. In regard to function, a soybean ERD15 homolog was character‐ ized as a transcription factor [25], a function not previously attributed to this protein family,

A Comprehensive Survey of International Soybean Research - Genetics, Physiology, Agronomy and Nitrogen

In respect to ERD genes described in soybean, the behavior of a group of eight genes (ERD1, ERD2, ERD3, ERD9, ERD10, ERD12, ERD15 gene and ERD16) was studied in response to stress. A soybean cDNA ERD1, homologous to yeast Hsp104, was isolated and characterized [46]. The soybean genes encoding homologs to yeast Hsp104 and Hsp101 have a high level of sequence identity to members of the family Clp [46]. When heterologously expressed in yeast, the soybean Hsp101 gene conferred greater thermotolerance to yeast [46]. Several genes related to Hsp70 (ERD2) have been described in soybean using proteomics studies. The first evidence of an ERD2-like protein in soybean was found during heat shock [47]. The presence of similar proteins was also found in response to osmotic and reticulum stress [48]. In respect to the orthologs of ERD3 in soybean, it was found that the GmIMT gene, which encodes a methyltransferase, acts by methylating the substrate D-ononitol. Its overexpres‐ sion in Arabidopsis causes an increase in drought and salinity tolerance [49]. When a gene encoding a soybean GST, an ortholog of ERD9, was over-expressed in tobacco plants, it con‐

Group 2 LEA (dehydrins or responsive to abscisic acid) proteins, such as ERD10 proteins, are postulated to protect macromolecules from damage by freezing, dehydration, ionic, or osmotic stress. In soybean, proteins of this group were studied for their structural and phys‐ io-chemical properties but little is discussed regarding the function of these proteins [51]. Overexpression of a member of the ERD12 family, GmAOC5, significantly increased oxida‐ tive stress resistance [52]. Within the ERD15 family, a soybean ortholog, GmERD15 has been functionally characterized as a transcription factor; in response to osmotic stress, GmERD15 acts to control transcription of a gene related to an integrative pathway in soybean [25]. Fi‐ nally, orthologs of ERD16 studied in soybean genes were identified with differential expres‐ sion during flood stress and hypoxia [53]. All genes studied related to different levels in response to stress, particularly drought and osmotic stress, demonstrating the conservation

Some ERD genes not yet studied in soybean deserve special attention because of either the proven involvement of a gene with similar functions in drought response in other organ‐ isms, or due to multiple copies of the soybean homolog. ERD5 and ERD7 family members have been characterized by activity in response to drought in other organisms (discussed be‐ low). They have not been studied in soybean; however, homology to soybean genes is dem‐

as reported by Kariola and colleagues [35] and Ziaf and colleagues [36].

**3. The ERD genes studied in soybean**

Relationships

480

ferred an increase in salinity and drought tolerance [50].

of function of this gene family in different plant species.

onstrated by the phylogenic tree shown in Figure 1.

Many studies on the roles and importance of ERD genes in soybean have become necessary due to lack of information about the importance of this group of genes during plant re‐

sponse to drought. The common feature of these genes is that their expression increases rap‐ idly in response to drought stress, suggesting that it is the first line of defense for plants against drought stress. It also suggests these genes may function to regulate expression of effector proteins and signaling pathways in response to stress.
