**2. The Early Responsive to Dehydration (ERD) genes and their functional diversity**

The ERD genes are defined as those genes that are rapidly activated during drought stress. The encoded proteins show a great structural and functional diversity and constitute the first line of defense against drought stress in plants (Table 1).

To date, a total of 16 complementary DNAs (cDNAs) for ERD genes have been isolated from 1-h-dehydrated Arabidopsis thaliana and only half of these are characterized in soybean. These genes encode proteins that include ClpA/B adenosine triphosphate (ATP)-dependent protease, heat shock protein (HSP) 70-1, S-adenosyl-methionine-dependent methyltransfer‐ ases, membrane protein, proline dehydrogenase, sugar transporter, senescence-related gene, glutathione-S-transferase, group II LEA (Late Embryogenesis Abundant) protein, chloro‐ plast and jasmonic acid biosynthesis protein, hydrophilic protein, and ubiquitin extension protein.



**Table 1.** ERD genes and their homologs in soybean. (\*) Indicates the characterized genes in soybean.

The ERD gene family has been collectively characterized as genes that are rapidly induced by dehydration [26]. ERD1 encodes a chloroplast ATP-dependent protease [26] and ERD2 encodes a, HSP70 [26], ERD3 encodes a methyltransferase in the pMT21 family [27], ERD4 encodes a membrane protein [28], ERD5 and ERD6 encode a mitochondrial dehydrogenase proline protein and a carbohydrates carrier protein, respectively [29-30]. ERD7 encodes a protein related to senescence and dehydration [31], ERD8 encodes a hsp81-family protein [26], ERD9, 11 and 13 belong to the family of glutathione S-transferase [32], ERD10 and 14 belong to the LEA protein family [33], ERD15 was first classified as a hydrophilic protein [34], which has a PAM2 interaction domain which interacts with poly-A tail binding pro‐ teins (PABP) [35].

ERD15 from Arabidopsis has been functionally characterized as a common regulator of the ab‐ scisic acid (ABA) response and salicylic acid (SA)-dependent defense pathway [35]. Overex‐ pression of ERD15 reduced ABA sensitivity, as the transgenic plants had reduced drought tolerance and failed to increase their freezing tolerance in response to hormone treatment [35]. In contrast, loss of ERD15 function due to gene silencing caused hypersensitivity to ABA, and the silenced plants displayed enhanced tolerance to both drought and freezing. The antagonis‐ tic effect of ERD15 activity on ABA signaling enhanced SA-dependent defense; overexpres‐ sion of ERD15 was associated with increased resistance to the bacterial necrotroph Erwinia carotovora and enhanced induction of systemic acquired resistance reporter genes [35]. The au‐ thors also addressed the antagonistic effect of ABA on SA-mediated defense by demonstrat‐ ing the enhanced expression of reporter genes for systemic acquired resistance in the plant null mutants abi1-1 and abi2-1, which are defective for ABA metabolism. These results together im‐ plicate Arabidopsis ERD15 as a shared component of ABA- and SA-mediated responses. The ERD15 homologs from Solanum licopersicum are 98% identical and belong to the same group as Arabidopsis ERD15, indicating a possible conservation of function [36]. Nevertheless, the to‐ mato protein clearly localizes to the nucleus and confers freezing tolerance when ectopically ex‐ pressed in transgenic tomato plants. These phenotypes are in marked contrast with the phenotypes displaying by ERD15-overexpressing Arabidopsis lines [35]. These contrasting re‐ sults in transgene overexpression studies suggest that the Arabidopsis and tomato ERD15 ho‐ mologs have divergent functions. Finally, a soybean homolog, GmERD15, has been described as an ER stress- and osmotic stress-induced transcription factor that activates the promoter and induces the expression of the NRP-B gene. These results indicate that GmERD15 functions as an upstream component of the NRP-mediated cell death signaling pathway, which is induced by ER and osmotic stress [37].

**Gene / GenBank accession number**

Relationships

478

*ERD7/*NP\_179374.1 Senescence/

*ERD8/*Y11827 Heat shock protein

*ERD10/*D17714*\** Group II LEA protein

*ERD9/*NP\_172508.4*\** Glutathione-S-

*ERD11/*D17672 Glutathione-S-

*ERD13/*D17673 Glutathione S-

*ERD16/*J05507*\** Ubiquitin extension

teins (PABP) [35].

dehydration related

protein

hsp81-2)

transferase

(lti29/lti45)

transferase

transferase

protein

*ERD12/*NP\_189204.1*\** Allene oxide cyclase [40] Glyma02g11020.1/ 2.3e-36 6

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

*ERD14/*D17715 Group II LEA protein [33] No homologs identified 0 *ERD15/*D30719*\** Hydrophilic protein [35] Glyma04g28560.1/ 3.5e-26 4

**Table 1.** ERD genes and their homologs in soybean. (\*) Indicates the characterized genes in soybean.

The ERD gene family has been collectively characterized as genes that are rapidly induced by dehydration [26]. ERD1 encodes a chloroplast ATP-dependent protease [26] and ERD2 encodes a, HSP70 [26], ERD3 encodes a methyltransferase in the pMT21 family [27], ERD4 encodes a membrane protein [28], ERD5 and ERD6 encode a mitochondrial dehydrogenase proline protein and a carbohydrates carrier protein, respectively [29-30]. ERD7 encodes a protein related to senescence and dehydration [31], ERD8 encodes a hsp81-family protein [26], ERD9, 11 and 13 belong to the family of glutathione S-transferase [32], ERD10 and 14 belong to the LEA protein family [33], ERD15 was first classified as a hydrophilic protein [34], which has a PAM2 interaction domain which interacts with poly-A tail binding pro‐

ERD15 from Arabidopsis has been functionally characterized as a common regulator of the ab‐ scisic acid (ABA) response and salicylic acid (SA)-dependent defense pathway [35]. Overex‐ pression of ERD15 reduced ABA sensitivity, as the transgenic plants had reduced drought tolerance and failed to increase their freezing tolerance in response to hormone treatment [35]. In contrast, loss of ERD15 function due to gene silencing caused hypersensitivity to ABA, and the silenced plants displayed enhanced tolerance to both drought and freezing. The antagonis‐

**Function Reference Best hit on soybean**

**genome / E value.**

[31] Glyma01g36960.1/ 3.5e-43 9

[26] Glyma08g44590.1/0 22

[32] Glyma01g04710.1/ 9.9e-22 87

[33] Glyma04g01130.1/ 4e-8 3

[32] Glyma02g17340.1/ 1.7e-5 52

[32] Glyma08g41960.1/ 3.7e-39 63

[33] Glyma03g35540.1/ 6.6e-50 100

**Similar genes in soybean**

> ERD16 encodes a ubiquitination extension protein [33]. Previous studies also showed that ERD13/AtGSTF10, a plant phi specific class GST ( Glutathione S-transferase) is an interac‐ tion protein with BAK1 (BRI1 Associated receptor Kinase 1). BAK1 is a co-receptor, which forms a receptor complex with BRI1 (brassinosteroid (BR) receptor) to regulate brassinoste‐ roid signaling in Arabidopsis. Overexpression of AtGSTF10 resulted in plants with in‐ creased tolerance to salt stress. In contrast, silencing AtGSTF10 by RNAi caused increased tolerance to abiotic stress and accelerated senescence of the transformants [38]. These find‐ ings suggest that modulation of ERD13/AtGSTF10 may regulate plant stress responses by regulating brassinosteroid signaling via interaction of AtGSTF10 with BAK1. ERD10 and 14 have chaperone activity, which aid in protein folding during stress [39]. ERD12 encodes a protein with homology to an allene oxide cyclase [40].

> With respect to expression controlled by phytohormones, ERD genes present varied functions and responses in ABA signaling, some being sensitive to ABA during germination and devel‐ opment [41], and /or are involved in stress tolerance [42]. Other genes are induced in response to more than one phytohormone [35]. Early Responsive to Dehydration 15 (ERD15) was char‐ acterized as a negative regulator of ABA and is induced by ABA, SA, injury and pathogen in‐ fection [35]. ABA application increases the expression of some members of the ERD group including ERD10 and 14 [34] while causing no effect on others, such as ERD2, 8 and 16 [33].

> Some contradictory data regarding the induction, as well as the function, of ERD genes are present in the literature [35-37]. Reduced expression of the ERD15 gene in response to wounding was reported [43], while an increased number of ERD15 transcripts were ob‐ served by other authors [35]. Furthermore, Arabidopsis plants showed increased tolerance to salt stress through the overexpression of AtSAT32, a key gene in the salinity-tolerance family Arabidopsis. These plants showed an increase in the number of ERD15 transcripts

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