Basic helix-loop-helix transcription factors JASMONATE-ASSOCIATED MYC2-LIKE1 (JAM1), JAM2, and JAM3 are negative regulators of jasmonate responses in Arabidopsis

Amino acid substitutions of GLY98, LEU245 and GLU543 in COI1 distinctively affect jasmonate-regulated male fertility in Arabidopsis

Jasmonate (JA) regulates various plant defense and developmental processes. The F-box protein CORONATINE INSENSITIVE 1 (COI1) perceives JA signals to mediate diverse plant responses including male fertility, root growth, anthocyanin accumulation, and defense against abiotic and biotic stresses. In this study, we carried out genetic, physiological and biochemical analysis on a series of coi1 mutant alleles, and found that different amino acid mutations in COI1 distinctively affect JA-regulated male fertility in Arabidopsis. All the JA responses are disrupted by the COI1 mutations W467 in coi1-1, Q343 (coi1-6), G369E (coi1-4), G98D (coi1-5), G155E (coi1-7), D452A (coi1-9) and L490A (coi1-10), though the coi1-5 mutant (COI1G98D) contains adequate COI1 protein (~ 60% of wild-type). Interestingly, the low basal level of COI1(E543K) in the coi1-8 mutant (~ 10% of wild-type COI1 level) is sufficient for maintaining male fertility ( ~50% of wild-type fertility); the coi1-2 mutant with low level of COI1(L245F) (~ 10% of wild-type) is male sterile under normal growth condition (22°C) but male fertile (~ 80% of wild-type fertility) at low temperature (16°C); however, both coi1-2 and coi1-8 are defective in the other JA responses (root growth, anthocyanin accumulation, and plant response to the pathogen Pst DC3000 infection).

Light regulation of plant defense

Precise allocation of limited resources between growth and defense is critical for plant survival. In shade-intolerant species, perception of competition signals by informational photoreceptors activates shade-avoidance responses and reduces the expression of defenses against pathogens and insects. The main mechanism underlying defense suppression is the simultaneous downregulation of jasmonate and salicylic acid signaling by low ratios of red:far-red radiation. Inactivation of phytochrome B by low red:far-red ratios appears to suppress jasmonate responses by altering the balance between DELLA and JASMONATE ZIM DOMAIN (JAZ) proteins in favor of the latter. Solar UVB radiation is a positive modulator of plant defense, signaling through jasmonate-dependent and jasmonate-independent pathways. Light, perceived by phytochrome B and presumably other photoreceptors, helps plants concentrate their defensive arsenals in photosynthetically valuable leaves. The discovery of connections between photoreceptors and defense signaling is revealing novel mechanisms that control key resource allocation decisions in plant canopies.

Comprehensive analysis of protein interactions between JAZ proteins and bHLH transcription factors that negatively regulate jasmonate signaling

Jasmonates have crucial roles in plant responses to biotic and abiotic stresses. Given the importance of transcriptional regulation in jasmonate-mediated stress responses, transcription factors are key regulators of jasmonate signaling. The transcription factors JASMONATE-ASSOCIATED MYC2-LIKE 1 (JAM1), JAM2, and JAM3 are negative regulators of jasmonate signaling, although the mechanisms that control the activities of these transcription factors remain unclear. To understand the regulatory mechanisms of JAM proteins, we used a yeast two-hybrid assay to screen for protein interaction partners of JAM1 and found that JAM1 interacted with JAZ proteins.

Two bHLH-type transcription factors, JA-ASSOCIATED MYC2-LIKE2 and JAM3, are transcriptional repressors and affect male fertility

The jasmonate (JA) plant hormones regulate responses to biotic and abiotic stress and aspects of plant development, including male fertility in Arabidopsis thaliana. The bHLH-type transcription factor JA-ASSOCIATED MYC2-LIKE1 (JAM1) negatively regulates JA signaling and gain-of-function JAM1 transgenic plants have impaired JA-mediated male fertility. Here we report that JAM2 and JAM3, 2 bHLHs closely related to JAM1, also act as transcriptional repressors. Moreover, overexpression of JAM2 and JAM3 also results in reduced male fertility. These results suggest that JAM1, JAM2, and JAM3 act redundantly as negative regulators of JA-mediated male fertility.