ABSTRACT The transcriptional regulatory network underlying ethylene‐governed starch‐to‐sugar conversion remains poorly understood. We elucidated the hierarchical regulatory cascade linking ethylene signalling to starch degradation in postharvest kiwifruit. Ethylene treatment accelerated fruit softening, starch degradation, and soluble sugar accumulation, whereas 1‐methylcyclopropene treatment produced opposite effects in kiwifruit. Weighted gene co‐expression network analysis identified 3 β‐amylase genes ( AcBAM3.1/3.3/3.5 ) and 16 transcription factors (TFs) as highly correlated with starch‐to‐sugar conversion. AcERF10 was isolated as a direct transcriptional activator of AcBAM3.1/3.3/3.5 and the ethylene biosynthetic gene AcACO1 . AcERF10 overexpression promoted starch degradation and sugar accumulation; silencing this gene resulted in opposite phenotypes. AcERF10 was directly activated by AcERF1 and AcHAT5—TFs that are induced by ethylene. AcERF1 bound to and activated the promoter of AcHAT5 , while AcHAT5 bound to the AcERF10 promoter and interacted with AcERF10 to synergistically activate expression of AcBAMs and AcACO1 , identifying a regulatory cascade of AcERF1‐AcHAT5‐AcERF10. Overexpression of either AcERF1 or AcHAT5 promoted downstream gene expression, accelerated starch degradation, and enhanced sugar accumulation, whereas silencing of either gene suppressed these processes. This study uncovers an ethylene‐triggered, multi‐layer transcriptional regulatory network that governs starch‐to‐sugar conversion during postharvest kiwifruit ripening, providing new mechanistic insights into ethylene‐regulated fruit quality development during postharvest storage.
ABSTRACT The cytosolic iron–sulfur (Fe‐S) cluster assembly (CIA) targeting complex mediates the maturation of cytosolic and nuclear Fe‐S proteins and governs core eukaryotic cellular processes. However, whether this complex contributes to plant disease resistance remains unclear. Here, we show that the Magnaporthe oryzae avirulence effector AvrPi9 targets the host CIA targeting complex to suppress rice blast resistance. AvrPi9 physically interacts with and stabilizes OsAE7, a core subunit of the CIA targeting complex. Using biochemical and genetic approaches, we demonstrate that OsAE7 facilitates Fe‐S protein maturation, including the Fe‐S protein aconitase OsACO1, and negatively regulates blast resistance in cooperation with another CIA targeting complex subunit, OsCIA1, and the carrier protein OsNAR1 in rice. Furthermore, ectopic expression of AvrPi9 enhances the activity of the CIA complex and the maturation of OsACO1. Knockout of OsACO1 elevates ferrous iron levels, triggers a reactive oxygen species (ROS) burst, and activates pathogenesis‐related gene transcription, thereby strengthening rice resistance to blast. Our findings reveal a critical role of the CIA targeting complex in plant disease resistance and uncover a novel virulence strategy whereby AvrPi9 hijacks the host CIA pathway to dampen basal resistance and promote infection.
ABSTRACT Rubisco activase (RCA) is critical for maintaining photosynthetic efficiency under heat stress, yet its regulatory mechanisms and functional diversification remain poorly understood. Here, we characterize a novel heat‐inducible RCA family member (RCA1), which plays a pivotal role in mediating multidimensional thermotolerance in a tropical azalea. Both heterologous and homologous overexpression of RCA1 significantly mitigated heat‐induced cellular damage and better maintained photosynthetic capacity, confirming its essential function in thermal resilience. Heat‐induced RCA1 expression is transcriptionally activated by a synergistic HSFA1‐HSFA2 complex and post‐transcriptionally fine‐tuned by extensive alternative splicing, forming a multilevel regulatory network under heat stress. Beyond its canonical Rubisco‐activating enzymatic activity, RCA1 exhibits an additional thermoprotective function that suppresses the thermal aggregation of several chloroplast proteins, such as Lhca2, PetC and PsaK. RCA1 also interacts with the constitutive RCA2, likely through heteromeric RCA complex assembly, which helps retain RCA2 in a soluble pool under heat stress. Evolutionary analyses reveal functional divergence within the RCA family, with convergent evolution of heat‐inducible RCA clades in Panicoideae grasses. Collectively, our findings uncover a novel dual‐functional heat‐inducible RCA, which provides a promising target for photosynthetic bioengineering to enhance crop thermotolerance and ensure agricultural sustainability under global warming.
ABSTRACT Stone cell lignification is a key determinant of pear fruit texture and commercial quality, and this process has been reported to be tightly coupled to cellular glucose availability. However, how glucose dose‐dependently targets transcription factor phosphorylation during lignin biosynthesis remains largely unknown. Using yeast two‐hybrid library screening and phosphorylation assays, we found that PbSnRK1, a glucose‐responsive kinase, interacts with and directly phosphorylates PbTCP13, thereby participating in the regulation of stone cell lignification. PbSnRK1 serves as an energy‐status sensor linking glucose signalling to biphasic regulation of lignin metabolism in pear. Under low‐glucose conditions, activated PbSnRK1 phosphorylates the transcription factor PbTCP13 at Ser265, targeting it for 26S proteasome‐mediated degradation and thereby derepressing PbMYB11‐ PbCCR1 cascade associated with lignin biosynthesis. Under high‐glucose conditions, suppressed PbSnRK1 kinase activity results in PbTCP13 protein accumulation, which restricts excessive lignification by both repressing PbCCR1 transcription and physically interacting with PbMYB11 to inhibit its transactivation capacity. This PbSnRK1‐PbTCP13‐PbMYB11 cascade, balanced by glucose concentration, acts as a molecular switch that activates stone cell formation and lignification at low‐glucose levels during early fruit development, while restricting excessive lignification at high‐glucose levels during later stages, providing new mechanistic insights into energy‐coupled secondary wall metabolism in fleshy fruits.
ABSTRACT The ripening of fleshy fruits is strongly regulated by a complex interplay between transcriptional regulation and post‐translational modifications (PTMs). However, the specific PTM regulatory networks involved in fruit ripening remain poorly understood. In this study, we identify MaAS1, an R2R3‐type MYB transcription factor, as a key negative regulator of banana fruit ripening. MaAS1 directly binds to the promoters of the ripening‐associated genes MaACS1 , MaPME23 and MaEXPA15 and represses their transcription. The mitogen‐activated protein kinase MaMPK3‐2 phosphorylates MaAS1 at three specific sites (Ser61, Thr92 and Ser120), thereby enhancing its transcriptional repressor activity and protein stability and ultimately suppressing fruit ripening. In contrast, the ethylene‐induced E3 ubiquitin ligase MaRNF4 mediates the ubiquitination and degradation of MaAS1, thereby promoting ripening. Notably, phosphorylation by MaMPK3‐2 antagonises MaRNF4‐mediated ubiquitination, maintaining MaAS1 levels and regulating ripening progression. Collectively, these findings reveal a regulatory module involving MaMPK3‐2, MaAS1 and MaRNF4, ultimately highlighting the intricate interplay between phosphorylation and ubiquitination in controlling fruit ripening, offering critical insights into the integrated regulatory network interconnecting transcription and PTMs during fruit ripening.
