CYP720A1 function in roots is required for flowering time and systemic acquired resistance in the foliage of Arabidopsis

Systemic acquired resistance (SAR) is an inducible defense mechanism that systemically enhances resistance against pathogens in foliar tissues. SAR, which engages salicylic acid (SA) signaling, shares molecular components with the autonomous pathway, which is involved in controlling flowering time in Arabidopsis thaliana. FLOWERING LOCUS D (FLD) is one such autonomous pathway component that is required for flowering time and the systemic accumulation of SA during SAR. Here, we show that CYP720A1, a putative cytochrome P450 monoxygenase, controls FLD expression and is required for the timing of flowering and the manifestation of SAR. The delayed flowering time in the cyp720a1 mutant correlated with the elevated transcript level of the floral repressor FLC, while the SAR deficiency phenotype of the cyp720a1 mutant correlated with the inability to systemically accumulate SA. CYP720A1 transcript abundance in shoots is poor compared with roots. Reciprocal root–shoot grafting confirmed that CYP720A1 function in the roots is critical for flowering time and SAR. We therefore suggest that root to shoot communication involving a CYP720A1-dependent factor contributes to the timing of reproductive development and defense in the foliage.

Root-to-Shoot Communication to Modulate Source-Sink Relationship in Tomato Depends on Phytochromes

Phytochromes have been reported as strategic photoreceptors that can modulate the partition of photoassimilates between source and sink. However, so far, it is unknown whether phytochrome accumulation in the root is part of the control mechanisms of the source-sink relationship that modulates root and shoot growth. Thus, the objective of this work was to investigate phytochrome involvement in the source-sink relationship and in the vegetative and reproductive development of tomato plants (Solanum lycopersicum L. cv. Micro-Tom or MT). The experimental design was completely randomized with four treatments, provided by grafting combinations between aurea (au), which is phytochrome deficient, and the near isogenic line MT: (MT/MT, au/au, MT/au and au/MT). We observed differentiated responses for many parameters analyzed. For example, the root dry mass accumulation and stern diameter obtained by MT/MT, MT/au and au/MT grafting were 33% and 31% higher, respectively, than those obtained by au/au. In the au/MT combination, there were greater root dry mass and total dry mass accumulations. Based on the changes in vegetative and reproductive development observed from grafting combinations between MT and the mutant au, we can conclude that phytochromes function in the control of photoassimilate partitioning between roots and stems during tomato growth.