Crossroads of stress responses, development and flowering regulation—the multiple roles of Cyclic Nucleotide Gated Ion Channel 2

Abstract

The Arabidopsis autoimmune mutant, defense-no death 1 (dnd1) is a null mutant of CYCLIC NUCLEOTIDE-GATED ION CHANNEL2 (AtCNGC2). dnd1 exhibits constitutive pathogen resistance responses including higher levels of endogenous salicylic acid (SA), which is an important signaling molecule for pathogen defense responses. Recently we have reported that dnd1 exhibits a significantly delayed flowering phenotype, indicating the involvement of AtCNGC2 in flowering transition. However, since SA has been known to influence flowering timing as a positive regulator, the delayed flowering phenotype in dnd1 was unexpected. In this study, we have asked whether SA is involved in the dnd1-mediated delayed flowering phenotype. In addition, in order to gain insight into the involvement of SA and CNGCs in flowering transition, we analyzed the flowering transition of cpr22, another CNGC mutant with a similar autoimmune phenotype as dnd1 (including high SA accumulation), and null mutants of several other CNGCs. Our data suggest that dnd1 does not require SA or SA signaling for its delayed flowering phenotype, while SA was responsible for the early flowering phenotype of cpr22. None of the other CNGC mutants besides AtCNGC4 (1) displayed an alteration in flowering transition. This indicates that AtCNGC2 and AtCNGC4 have a unique role controlling flowering timing and this function is independent from its role in pathogen defense.

How does the multifaceted plant hormone salicylic acid combat disease in plants and are similar mechanisms utilized in humans?

“…SA also has long been proposed as a signal for flowering [11]. Consistent with this possibility, the early flowering phenotype observed in several Arabidopsis mutants correlates with, and is dependent on, elevated SA levels [12–15]. In addition, flowering was delayed in one study of SA-deficient Arabidopsis [16], although others failed to observe this phenomenon [17, 18].…”

“…In addition, flowering was delayed in one study of SA-deficient Arabidopsis [16], although others failed to observe this phenomenon [17, 18]. Interestingly, several proteins that regulate both flowering and resistance signaling have been identified [12, 13, 15, 17–21]. While this finding suggests an interconnection between flowering and disease resistance [22], it is clearly complex: some of these proteins regulate both resistance and flowering in an SA-dependent manner, whereas several others regulate resistance via an SA-dependent pathway but positively or negatively regulate flowering via an SA-independent mechanism.…”

Down-regulation of Arabidopsis DND1 orthologs in potato and tomato leads to broad-spectrum resistance to late blight and powdery mildew

“…In Arabidopsis , DND1/CNGC2 has been reported to play a role in flowering timing and fertility (Chaiwongsar et al 2009 ; Chin et al 2013 ). Fortuna et al ( 2015 ) reported that the role of DND1 in flowering timing is independent from SA accumulation, and independent from its role in pathogen defense. Further investigations are necessary to determine whether disease resistance can be achieved in tomato without reduced fertility by decreased expression level or altered functionality of SlDND1 .…”

Phylogeny and evolution of plant cyclic nucleotide-gated ion channel (CNGC) gene family and functional analyses of tomatoCNGCs

“… 25 – 30 Several members of Arabidopsis CNGC Groups I–III regulate various functions such as plant development and stress tolerance, 25 , 31 seed germination, 32 plant growth, 33 pollen fertility under stress, 5 pollen tip growth 34 and pathogen defence. 35 , 36 However, AtCNGC2 and AtCNGC4 , members of Group IVb, played their role in disease resistance against various pathogens and in thermotolerance, 29 , 37 – 44 while AtCNGC19 and AtCNGC20 , members of Group IVa, are involved in abiotic salt stress responses. 19 , 45 – 47 Whether plant CNGC genes are functionally distinguished in a group-dependent manner is not clear.…”