The Calmodulin-Binding Transcription Factor SIGNAL RESPONSIVE1 is a Novel Regulator of Glucosinolate Metabolism and Herbivory Tolerance in Arabidopsis

Abstract

The Arabidopsis Ca(2+)/calmodulin (CaM)-binding transcription factor SIGNAL RESPONSIVE1 (AtSR1/CAMTA3) was previously identified as a key negative regulator of plant immune responses. Here, we report a new role for AtSR1 as a critical component of plant defense against insect herbivory. Loss of AtSR1 function impairs tolerance to feeding by the generalist herbivore Trichoplusia ni as well as wound-induced jasmonate accumulation. The susceptibility of the atsr1 mutant is associated with decreased total glucosinolate (GS) levels. The two key herbivory deterrents, indol-3-ylmethyl (I3M) and 4-methylsulfinylbutyl (4MSOB), showed the most significant reductions in atsr1 plants. Further, changes in AtSR1 transcript levels led to altered expression of several genes involved in GS metabolism including IQD1, MYB51 and AtST5a. Overall, our results establish AtSR1 as an important component of plant resistance to insect herbivory as well as one of only three described proteins involved in Ca(2+)/CaM-dependent signaling to function in the regulation of GS metabolism, providing a novel avenue for future investigations of plant-insect interactions.

Recent Advances in Calcium/Calmodulin-Mediated Signaling with an Emphasis on Plant-Microbe Interactions

“…In addition, it was observed that elevated SA levels in atsr1 mutant plants have a negative impact on both basal and induced biosynthesis of jasmonates, a critical hormone-mediated wounding response in plants . Furthermore, compared with the wild type, the atsr1 mutant accumulates less of the insect repellent metabolite glucosinolate, and this coincides with the altered expression of several genes involved in glucosinolate metabolism, such as MYB51, AtST5a, and IQD1 (Laluk et al, 2012). In a different line of research, CAMTA3 was shown to recognize the conserved DNA motif 2 (CM2, CCGCGT) in the promoter of CBF2, a critical transcription factor required for Arabidopsis cold acclimation and the subsequent establishment of freezing tolerance as well as the regulation of coldinduced gene expression (Doherty et al, 2009).…”

“…Similar to the function of CAMTA3, OsCBT, a CAMTA member from rice, also plays a negative role in regulating rice defense against both the bacterial pathogen Xanthomonas oryzae pv oryzae and the rice blast fungus Magnaporthe grisea (Koo et al, 2009). Very recently, CAMTA3 was shown to play a critical role in plant defense against insect herbivory (Laluk et al, 2012;Qiu et al, 2012). atsr1/camta3 null mutants are more vulnerable to herbivore attack, and CaM binding was shown to be required for AtSR1/CAMTA3 in maintaining normal levels of plant resistance to herbivore attack.…”

Metabolomic Assessment Reveals an Elevated Level of Glucosinolate Content in CaCl2 Treated Broccoli Microgreens

“…52 Knockout of another calcium/calmodulin regulated transcription factor AtSR1/CaMTA3 resulted in the decreased GL levels and plant defense against insect herbivory. 53 Previously, we observed that calcium treatment retarded the broccoli microgreen decay during storage and extended shelf life. 15 This could be contributed, at least partially, by the increased GL levels thereby enhancing the microgreen stress tolerance and defense.…”

Calmodulin-binding transcription activators and perspectives for applications in biotechnology

“…Two key herbivory deterrents: indol-3-ylmethyl and 4-methylsulfinylbutyl, were significantly reduced in camta3 mutant plants. The expression levels of several genes involved in glucosinolate (GS) metabolism were also found to be altered in the camta3 mutant, suggesting a role of CAMTA3 in regulating GS metabolism (Laluk et al 2012). Furthermore, after herbivore attack, the SA level was elevated and the jasmonic acid (JA) level was decreased in the camta3 mutant.…”